[PATCH bpf-next v4 00/25] Resilient Queued Spin Lock

[PATCH bpf-next v4 00/25] Resilient Queued Spin Lock

[Kumar Kartikeya Dwivedi]

Changelog:
----------
v3 -> v4
v4: https://lore.kernel.org/bpf/20250303152305.3195648-1-memxor@gmail.com

 * Fix bisectability problem by reordering locktorture commit before
   Makefile commit.
 * Add EXPORT_SYMBOL_GPL to all used symbols and variables by consumers.
 * Skip BPF selftest when nrprocs < 2.
 * Fix kdoc to describe return value for res_spin_lock, slowpath.
 * Move kernel/locking/rqspinlock.{c,h} to kernel/bpf/rqspinlock.{c,h}.

v2 -> v3
v2: https://lore.kernel.org/bpf/20250206105435.2159977-1-memxor@gmail.com

 * Add ifdef's to fallback to Ankur's patch when it gets in, until then
   copy-paste the implementation.
 * Change the meaning of RES_DEF_TIMEOUT from two critical section
   lengths to one for clarity, and use RES_DEF_TIMEOUT * 2 where needed.
 * Use NSEC_PER_SEC as timeout for TAS fallback.
 * Add Closes: tags for known syzbot reports.
 * Change timeout for TAS fallback to 1 second.
 * Fix more kernel test robot errors.
 * More comments about smp_wmb in release_held_lock_entry interaction.
 * Change RES_NR_HELD to 31.
 * Address comments from Peter, Eduard, Alexei.

v1 -> v2
v1: https://lore.kernel.org/bpf/20250107140004.2732830-1-memxor@gmail.com

 * Address nits from Waiman and Peter
 * Fix arm64 WFE bug pointed out by Peter.
 * Fix incorrect memory ordering in release_held_lock_entry, and
   document subtleties. Explain why release is sufficient in unlock
   but not in release_held_lock_entry.
 * Remove dependence on CONFIG_QUEUED_SPINLOCKS and introduce a
   test-and-set fallback when queued spinlock support is missing on an
   architecture.
 * Enforce FIFO ordering for BPF program spin unlocks.
 * Address comments from Eduard on verifier plumbing.
 * Add comments as suggested by Waiman.
 * Refactor paravirt TAS lock to use the implemented TAS fallback.
 * Use rqspinlock_t as the type throughout so that it can be replaced
   with a non-qspinlock type in case of fallback.
 * Testing and benchmarking on arm64, added numbers to the cover letter.
 * Fix kernel test robot errors.
 * Fix a BPF selftest bug leading to spurious failures on arm64.

Introduction
------------

This patch set introduces Resilient Queued Spin Lock (or rqspinlock with
res_spin_lock() and res_spin_unlock() APIs).

This is a qspinlock variant which recovers the kernel from a stalled
state when the lock acquisition path cannot make forward progress. This
can occur when a lock acquisition attempt enters a deadlock situation
(e.g. AA, or ABBA), or more generally, when the owner of the lock (which
we’re trying to acquire) isn’t making forward progress.

The cover letter provides an overview of the motivation, design, and
alternative approaches. We then provide evaluation numbers showcasing
that while rqspinlock incurs overhead, the performance of rqspinlock
approaches that of the normal qspinlock used by the kernel.

The evaluations for rqspinlock were performed by replacing the default
qspinlock implementation with it and booting the kernel to run the
experiments. Support for locktorture is also included with numbers in
this series.

The cover letter's design section provides an overview of the
algorithmic approach. A technical document describing the implementation
in more detail is available here:
https://github.com/kkdwivedi/rqspinlock/blob/main/rqspinlock.pdf

We have a WIP TLA+ proof for liveness and mutual exclusion of rqspinlock
built on top of the qspinlock TLA+ proof from Catalin Marinas [3]. We
will share more details and the links in the near future.

Motivation
----------

In regular kernel code, usage of locks is assumed to be correct, so as
to avoid deadlocks and stalls by construction, however, the same is not
true for BPF programs. Users write normal C code and the in-kernel eBPF
runtime ensures the safety of the kernel by rejecting unsafe programs.
Users can upload programs that use locks in an improper fashion, and may
cause deadlocks when these programs run inside the kernel. The verifier
is responsible for rejecting such programs from being loaded into the
kernel.

Until now, the eBPF verifier ensured deadlock safety by only permitting
one lock acquisition at a time, and by preventing any functions to be
called from within the critical section. Additionally, only a few
restricted program types are allowed to call spin locks. As the usage of
eBPF grows (e.g. with sched_ext) beyond its conventional application in
networking, tracing, and security, the limitations on locking are
becoming a bottleneck for users.

The rqspinlock implementation allows us to permit more flexible locking
patterns in BPF programs, without limiting them to the subset that can
be proven safe statically (which is fairly small, and requires complex
static analysis), while ensuring that the kernel will recover in case we
encounter a locking violation at runtime. We make a tradeoff here by
accepting programs that may potentially have deadlocks, and recover the
kernel quickly at runtime to ensure availability.

Additionally, eBPF programs attached to different parts of the kernel
can introduce new control flow into the kernel, which increases the
likelihood of deadlocks in code not written to handle reentrancy. There
have been multiple syzbot reports surfacing deadlocks in internal kernel
code due to the diverse ways in which eBPF programs can be attached to
different parts of the kernel.  By switching the BPF subsystem’s lock
usage to rqspinlock, all of these issues can be mitigated at runtime.

This spin lock implementation allows BPF maps to become safer and remove
mechanisms that have fallen short in assuring safety when nesting
programs in arbitrary ways in the same context or across different
contexts. The red diffs due to patches 16-18 demonstrate this
simplification.

>  kernel/bpf/hashtab.c         | 102 ++++++++++++++++++++++++++++++++--------------------------...
>  kernel/bpf/lpm_trie.c        |  25 ++++++++++++++-----------
>  kernel/bpf/percpu_freelist.c | 113 +++++++++++++++++++++++++---------------------------------...
>  kernel/bpf/percpu_freelist.h |   4 ++--
>  4 files changed, 73 insertions(+), 171 deletions(-)

Design
------

Deadlocks mostly manifest as stalls in the waiting loops of the
qspinlock slow path. Thus, using stalls as a signal for deadlocks avoids
introducing cost to the normal fast path, and ensures bounded
termination of the waiting loop. Our recovery algorithm is focused on
terminating the waiting loops of the qspinlock algorithm when it gets
stuck, and implementing bespoke recovery procedures for each class of
waiter to restore the lock to a usable state. Deadlock detection is the
main mechanism used to provide faster recovery, with the timeout
mechanism acting as a final line of defense.

Deadlock Detection
~~~~~~~~~~~~~~~~~~
We handle two cases of deadlocks: AA deadlocks (attempts to acquire the
same lock again), and ABBA deadlocks (attempts to acquire two locks in
the opposite order from two distinct threads). Variants of ABBA
deadlocks may be encountered with more than two locks being held in the
incorrect order. These are not diagnosed explicitly, as they reduce to
ABBA deadlocks.

Deadlock detection is triggered immediately when beginning the waiting
loop of a lock slow path.

While timeouts ensure that any waiting loops in the locking slow path
terminate and return to the caller, it can be excessively long in some
situations. While the default timeout is short (0.5s), a stall for this
duration inside the kernel can set off alerts for latency-critical
services with strict SLOs.  Ideally, the kernel should recover from an
undesired state of the lock as soon as possible.

A multi-step strategy is used to recover the kernel from waiting loops
in the locking algorithm which may fail to terminate in a bounded amount
of time.

 * Each CPU maintains a table of held locks. Entries are inserted and
   removed upon entry into lock, and exit from unlock, respectively.
 * Deadlock detection for AA locks is thus simple: we have an AA
   deadlock if we find a held lock entry for the lock we’re attempting
   to acquire on the same CPU.
 * During deadlock detection for ABBA, we search through the tables of
   all other CPUs to find situations where we are holding a lock the
   remote CPU is attempting to acquire, and they are holding a lock we
   are attempting to acquire. Upon encountering such a condition, we
   report an ABBA deadlock.
 * We divide the duration between entry time point into the waiting loop
   and the timeout time point into intervals of 1 ms, and perform
   deadlock detection until timeout happens. Upon entry into the slow
   path, and then completion of each 1 ms interval, we perform detection
   of both AA and ABBA deadlocks. In the event that deadlock detection
   yields a positive result, the recovery happens sooner than the
   timeout.  Otherwise, it happens as a last resort upon completion of
   the timeout.

Timeouts
~~~~~~~~
Timeouts act as final line of defense against stalls for waiting loops.
The ‘ktime_get_mono_fast_ns’ function is used to poll for the current
time, and it is compared to the timestamp indicating the end time in the
waiter loop. Each waiting loop is instrumented to check an extra
condition using a macro. Internally, the macro implementation amortizes
the checking of the timeout to avoid sampling the clock in every
iteration.  Precisely, the timeout checks are invoked every 64k
iterations.

Recovery
~~~~~~~~
There is extensive literature in academia on designing locks that
support timeouts [0][1], as timeouts can be used as a proxy for
detecting the presence of deadlocks and recovering from them, without
maintaining explicit metadata to construct a waits-for relationship
between two threads at runtime.

In case of rqspinlock, the key simplification in our algorithm comes
from the fact that upon a timeout, waiters always leave the queue in
FIFO order.  As such, the timeout is only enforced by the head of the
wait queue, while other waiters rely on the head to signal them when a
timeout has occurred and when they need to exit. We don’t have to
implement complex algorithms and do not need extra synchronization for
waiters in the middle of the queue timing out before their predecessor
or successor, unlike previous approaches [0][1].

There are three forms of waiters in the original queued spin lock
algorithm.  The first is the waiter which acquires the pending bit and
spins on the lock word without forming a wait queue. The second is the
head waiter that is the first waiter heading the wait queue. The third
form is of all the non-head waiters queued behind the head, waiting to
be signalled through their MCS node to overtake the responsibility of
the head.

In rqspinlock's recovery algorithm, we are concerned with the second and
third kind. First, we augment the waiting loop of the head of the wait
queue with a timeout. When this timeout happens, all waiters part of the
wait queue will abort their lock acquisition attempts. This happens in
three steps.

 * First, the head breaks out of its loop waiting for pending and locked
   bits to turn to 0, and non-head waiters break out of their MCS node
   spin (more on that later).
 * Next, every waiter (head or non-head) attempts to check whether they
   are also the tail waiter, in such a case they attempt to zero out the
   tail word and allow a new queue to be built up for this lock. If they
   succeed, they have no one to signal next in the queue to stop
   spinning.
 * Otherwise, they signal the MCS node of the next waiter to break out
   of its spin and try resetting the tail word back to 0. This goes on
   until the tail waiter is found. In case of races, the new tail will
   be responsible for performing the same task, as the old tail will
   then fail to reset the tail word and wait for its next pointer to be
   updated before it signals the new tail to do the same.

Timeout Bound
~~~~~~~~~~~~~
The timeout is applied by two types of waiters: the pending bit waiter
and the wait queue head waiter. As such, for the pending waiter, only
the lock owner is ahead of it, and for the wait queue head waiter, only
the lock owner and the pending waiter take precedence in executing their
critical sections.

We define the timeout value to span at most 1 critical section length,
and then use the appropriate value (default, or default x 2) depending
on if we are the pending waiter or head of wait queue.

Therefore, the waiting loop wait can span at most 2 critical section
lengths, and thus, it is unaffected by the amount of contention or the
number of CPUs on the host. Non-head waiters simply wait for the wait
queue head to signal them on a timeout.

In Meta's production, we have noticed uncore PMU reads and SMIs
consuming tens of msecs. While these events are rare, a 0.25 second
timeout should absorb such tail events and not raise false alarms for
timeouts. We will continue monitoring this in production and adjust the
timeout if necessary in the future.

More details of the recovery algorithm is described in patch 9 and a
detailed description is available at [2].

Alternatives
------------

Lockdep: We do not rely on the lockdep facility for reporting violations
for primarily two reasons:

* Overhead: The lockdep infrastructure can add significant overhead to
  the lock acquisition path, and is not recommended for use in
  production due to this reason. While the report is more useful and
  exhaustive, the overhead can be prohibitive, especially as BPF
  programs run in hot paths of the kernel.  Moreover, it also increases
  the size of the lock word to store extra metadata, which is not
  feasible for BPF spin locks that are 4-bytes in size today (similar to
  qspinlock).

* Debug Tool: Lockdep is intended to be used as a debugging facility,
  providing extra context to the user about the locking violations
  occurring during runtime. It is always turned off on all production
  kernels, therefore isn’t available most of the time.

We require a mechanism for detecting common variants of deadlocks that
is always available in production kernels and never turned off. At the
same time, it must not introduce overhead in terms of time (for the slow
path) and memory (for the lock word size).

Evaluation
----------

We run benchmarks that stress locking scalability and perform comparison
against the baseline (qspinlock). For the rqspinlock case, we replace
the default qspinlock with it in the kernel, such that all spin locks in
the kernel use the rqspinlock slow path. As such, benchmarks that stress
kernel spin locks end up exercising rqspinlock.

Evaluation setup
~~~~~~~~~~~~~~~~

We set the CPU governor to performance for all experiments.

Note: Numbers for arm64 have been obtained without the no-WFE fallback
in this series, to perform a fair comparison with the WFE using
qspinlock baseline.

x86_64:

Intel Xeon Platinum 8468 (Sapphire Rapids)
96 cores (48 x 2 sockets)
2 threads per core, 0-95, siblings from 96-191
2 NUMA nodes (every 48 cores), 2 LLCs (every 48 cores), 1 LLC per NUMA node
Hyperthreading enabled

arm64:

Ampere Max Neoverse-N1 256-Core Processor
256 cores (128 cores x 2 sockets)
1 thread per core
2 NUMA nodes (every 128 cores), 1 L2 per core (256 instances), no shared L3
No hyperthreading available

The locktorture experiment is run for 30 seconds.
Average of 25 runs is used for will-it-scale, after an initial warm up.

More information on the locks contended in the will-it-scale experiments
is available in the evaluation section of the CNA paper, in table 1 [4].

Legend:
 QL - qspinlock (avg. throughput)
 RQL - rqspinlock (avg. throughput)

Results
~~~~~~~

locktorture - x86_64

Threads QL		RQL		Speedup
-----------------------------------------------
1	46910437	45057327	0.96
2	29871063	25085034	0.84
4	13876024	19242776	1.39
8	14638499	13346847	0.91
16	14380506	14104716	0.98
24	17278144	15293077	0.89
32	19494283	17826675	0.91
40	27760955	21002910	0.76
48	28638897	26432549	0.92
56	29336194	26512029	0.9
64	30040731	27421403	0.91
72	29523599	27010618	0.91
80	28846738	27885141	0.97
88	29277418	25963753	0.89
96	28472339	27423865	0.96
104	28093317	26634895	0.95
112	29914000	27872339	0.93
120	29199580	26682695	0.91
128	27755880	27314662	0.98
136	30349095	27092211	0.89
144	29193933	27805445	0.95
152	28956663	26071497	0.9
160	28950009	28183864	0.97
168	29383520	28135091	0.96
176	28475883	27549601	0.97
184	31958138	28602434	0.89
192	31342633	33394385	1.07

will-it-scale open1_threads - x86_64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	1396323.92	7373.12		0.53	1366616.8	4152.08		0.3	0.98
2	1844403.8	3165.26		0.17	1700301.96	2396.58		0.14	0.92
4	2370590.6	24545.54	1.04	1655872.32	47938.71	2.9	0.7
8	2185227.04	9537.9		0.44	1691205.16	9783.25		0.58	0.77
16	2110672.36	10972.99	0.52	1781696.24	15021.43	0.84	0.84
24	1655042.72	18037.23	1.09	2165125.4	5422.54		0.25	1.31
32	1738928.24	7166.64		0.41	1829468.24	9081.59		0.5	1.05
40	1854430.52	6148.24		0.33	1731062.28	3311.95		0.19	0.93
48	1766529.96	5063.86		0.29	1749375.28	2311.27		0.13	0.99
56	1303016.28	6168.4		0.47	1452656		7695.29		0.53	1.11
64	1169557.96	4353.67		0.37	1287370.56	8477.2		0.66	1.1
72	1036023.4	7116.53		0.69	1135513.92	9542.55		0.84	1.1
80	1097913.64	11356		1.03	1176864.8	6771.41		0.58	1.07
88	1123907.36	12843.13	1.14	1072416.48	7412.25		0.69	0.95
96	1166981.52	9402.71		0.81	1129678.76	9499.14		0.84	0.97
104	1108954.04	8171.46		0.74	1032044.44	7840.17		0.76	0.93
112	1000777.76	8445.7		0.84	1078498.8	6551.47		0.61	1.08
120	1029448.4	6992.29		0.68	1093743		8378.94		0.77	1.06
128	1106670.36	10102.15	0.91	1241438.68	23212.66	1.87	1.12
136	1183776.88	6394.79		0.54	1116799.64	18111.38	1.62	0.94
144	1201122		25917.69	2.16	1301779.96	15792.6		1.21	1.08
152	1099737.08	13567.82	1.23	1053647.2	12704.29	1.21	0.96
160	1031186.32	9048.07		0.88	1069961.4	8293.18		0.78	1.04
168	1068817		16486.06	1.54	1096495.36	14021.93	1.28	1.03
176	966633.96	9623.27		1	1081129.84	9474.81		0.88	1.12
184	1004419.04	12111.11	1.21	1037771.24	12001.66	1.16	1.03
192	1088858.08	16522.93	1.52	1027943.12	14238.57	1.39	0.94

will-it-scale open2_threads - x86_64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	1337797.76	4649.19		0.35	1332609.4	3813.14		0.29	1
2	1598300.2	1059.93		0.07	1771891.36	5667.12		0.32	1.11
4	1736573.76	13025.33	0.75	1396901.2	2682.46		0.19	0.8
8	1794367.84	4879.6		0.27	1917478.56	3751.98		0.2	1.07
16	1990998.44	8332.78		0.42	1864165.56	9648.59		0.52	0.94
24	1868148.56	4248.23		0.23	1710136.68	2760.58		0.16	0.92
32	1955180		6719		0.34	1936149.88	1980.87		0.1	0.99
40	1769646.4	4686.54		0.26	1729653.68	4551.22		0.26	0.98
48	1724861.16	4056.66		0.24	1764900		971.11		0.06	1.02
56	1318568		7758.86		0.59	1385660.84	7039.8		0.51	1.05
64	1143290.28	5351.43		0.47	1316686.6	5597.69		0.43	1.15
72	1196762.68	10655.67	0.89	1230173.24	9858.2		0.8	1.03
80	1126308.24	6901.55		0.61	1085391.16	7444.34		0.69	0.96
88	1035672.96	5452.95		0.53	1035541.52	8095.33		0.78	1
96	1030203.36	6735.71		0.65	1020113.48	8683.13		0.85	0.99
104	1039432.88	6583.59		0.63	1083902.48	5775.72		0.53	1.04
112	1113609.04	4380.62		0.39	1072010.36	8983.14		0.84	0.96
120	1109420.96	7183.5		0.65	1079424.12	10929.97	1.01	0.97
128	1095400.04	4274.6		0.39	1095475.2	12042.02	1.1	1
136	1071605.4	11103.73	1.04	1114757.2	10516.55	0.94	1.04
144	1104147.2	9714.75		0.88	1044954.16	7544.2		0.72	0.95
152	1164280.24	13386.15	1.15	1101213.92	11568.49	1.05	0.95
160	1084892.04	7941.25		0.73	1152273.76	9593.38		0.83	1.06
168	983654.76	11772.85	1.2	1111772.28	9806.83		0.88	1.13
176	1087544.24	11262.35	1.04	1077507.76	9442.02		0.88	0.99
184	1101682.4	24701.68	2.24	1095223.2	16707.29	1.53	0.99
192	983712.08	13453.59	1.37	1051244.2	15662.05	1.49	1.07

will-it-scale lock1_threads - x86_64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	4307484.96	3959.31		0.09	4252908.56	10375.78	0.24	0.99
2	7701844.32	4169.88		0.05	7219233.52	6437.11		0.09	0.94
4	14781878.72	22854.85	0.15	15260565.12	37305.71	0.24	1.03
8	12949698.64	99270.42	0.77	9954660.4	142805.68	1.43	0.77
16	12947690.64	72977.27	0.56	10865245.12	49520.31	0.46	0.84
24	11142990.64	33200.39	0.3	11444391.68	37884.46	0.33	1.03
32	9652335.84	22369.48	0.23	9344086.72	21639.22	0.23	0.97
40	9185931.12	5508.96		0.06	8881506.32	5072.33		0.06	0.97
48	9084385.36	10871.05	0.12	8863579.12	4583.37		0.05	0.98
56	6595540.96	33100.59	0.5	6640389.76	46619.96	0.7	1.01
64	5946726.24	47160.5		0.79	6572155.84	91973.73	1.4	1.11
72	6744894.72	43166.65	0.64	5991363.36	80637.56	1.35	0.89
80	6234502.16	118983.16	1.91	5157894.32	73592.72	1.43	0.83
88	5053879.6	199713.75	3.95	4479758.08	36202.27	0.81	0.89
96	5184302.64	99199.89	1.91	5249210.16	122348.69	2.33	1.01
104	4612391.92	40803.05	0.88	4850209.6	26813.28	0.55	1.05
112	4809209.68	24070.68	0.5	4869477.84	27489.04	0.56	1.01
120	5130746.4	34265.5		0.67	4620047.12	44229.54	0.96	0.9
128	5376465.28	95028.05	1.77	4781179.6	43700.93	0.91	0.89
136	5453742.4	86718.87	1.59	5412457.12	40339.68	0.75	0.99
144	5805040.72	84669.31	1.46	5595382.48	68701.65	1.23	0.96
152	5842897.36	31120.33	0.53	5787587.12	43521.68	0.75	0.99
160	5837665.12	14179.44	0.24	5118808.72	45193.23	0.88	0.88
168	5660332.72	27467.09	0.49	5104959.04	40891.75	0.8	0.9
176	5180312.24	28656.39	0.55	4718407.6	58734.13	1.24	0.91
184	4706824.16	50469.31	1.07	4692962.64	92266.85	1.97	1
192	5126054.56	51082.02	1	4680866.8	58743.51	1.25	0.91

will-it-scale lock2_threads - x86_64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	4316091.2	4933.28		0.11	4293104		30369.71	0.71	0.99
2	3500046.4	19852.62	0.57	4507627.76	23667.66	0.53	1.29
4	3639098.96	26370.65	0.72	3673166.32	30822.71	0.84	1.01
8	3714548.56	49953.44	1.34	4055818.56	71630.41	1.77	1.09
16	4188724.64	105414.49	2.52	4316077.12	68956.15	1.6	1.03
24	3737908.32	47391.46	1.27	3762254.56	55345.7		1.47	1.01
32	3820952.8	45207.66	1.18	3710368.96	52651.92	1.42	0.97
40	3791280.8	28630.55	0.76	3661933.52	37671.27	1.03	0.97
48	3765721.84	59553.83	1.58	3604738.64	50861.36	1.41	0.96
56	3175505.76	64336.17	2.03	2771022.48	66586.99	2.4	0.87
64	2620294.48	71651.34	2.73	2650171.68	44810.83	1.69	1.01
72	2861893.6	86542.61	3.02	2537437.2	84571.75	3.33	0.89
80	2976297.2	83566.43	2.81	2645132.8	85992.34	3.25	0.89
88	2547724.8	102014.36	4	2336852.16	80570.25	3.45	0.92
96	2945310.32	82673.25	2.81	2513316.96	45741.81	1.82	0.85
104	3028818.64	90643.36	2.99	2581787.52	52967.48	2.05	0.85
112	2546264.16	102605.82	4.03	2118812.64	62043.19	2.93	0.83
120	2917334.64	112220.01	3.85	2720418.64	64035.96	2.35	0.93
128	2906621.84	69428.1		2.39	2795310.32	56736.87	2.03	0.96
136	2841833.76	105541.11	3.71	3063404.48	62288.94	2.03	1.08
144	3032822.32	134796.56	4.44	3169985.6	149707.83	4.72	1.05
152	2557694.96	62218.15	2.43	2469887.6	68343.78	2.77	0.97
160	2810214.72	61468.79	2.19	2323768.48	54226.71	2.33	0.83
168	2651146.48	76573.27	2.89	2385936.64	52433.98	2.2	0.9
176	2720616.32	89026.19	3.27	2941400.08	59296.64	2.02	1.08
184	2696086		88541.24	3.28	2598225.2	76365.7		2.94	0.96
192	2908194.48	87023.91	2.99	2377677.68	53299.82	2.24	0.82

locktorture - arm64

Threads QL		RQL		Speedup
-----------------------------------------------
1	43320464	44718174	1.03
2	21056971	29255448	1.39
4	16040120	11563981	0.72
8	12786398	12838909	1
16	13646408	13436730	0.98
24	13597928	13669457	1.01
32	16456220	14600324	0.89
40	16667726	13883101	0.83
48	14347691	14608641	1.02
56	15624580	15180758	0.97
64	18105114	16009137	0.88
72	16606438	14772256	0.89
80	16550202	14124056	0.85
88	16716082	15930618	0.95
96	16489242	16817657	1.02
104	17915808	17165324	0.96
112	17217482	21343282	1.24
120	20449845	20576123	1.01
128	18700902	20286275	1.08
136	17913378	21142921	1.18
144	18225673	18971921	1.04
152	18374206	19229854	1.05
160	23136514	20129504	0.87
168	21096269	17167777	0.81
176	21376794	21594914	1.01
184	23542989	20638298	0.88
192	22793754	20655980	0.91
200	20933027	19628316	0.94
208	23105684	25572720	1.11
216	24158081	23173848	0.96
224	23388984	22485353	0.96
232	21916401	23899343	1.09
240	22292129	22831784	1.02
248	25812762	22636787	0.88
256	24294738	26127113	1.08

will-it-scale open1_threads - arm64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	844452.32	801		0.09	804936.92	900.25		0.11	0.95
2	1309419.08	9495.78		0.73	1265080.24	3171.13		0.25	0.97
4	2113074.24	5363.19		0.25	2041158.28	7883.65		0.39	0.97
8	1916650.96	15749.86	0.82	2039850.04	7562.87		0.37	1.06
16	1835540.72	12940.45	0.7	1937398.56	11461.15	0.59	1.06
24	1876760.48	12581.67	0.67	1966659.16	10012.69	0.51	1.05
32	1834525.6	5571.08		0.3	1929180.4	6221.96		0.32	1.05
40	1851592.76	7848.18		0.42	1937504.44	5991.55		0.31	1.05
48	1845067		4118.68		0.22	1773331.56	6068.23		0.34	0.96
56	1742709.36	6874.03		0.39	1716184.92	6713.16		0.39	0.98
64	1685339.72	6688.91		0.4	1676046.16	5844.06		0.35	0.99
72	1694838.84	2433.41		0.14	1821189.6	2906.89		0.16	1.07
80	1738778.68	2916.74		0.17	1729212.6	3714.41		0.21	0.99
88	1753131.76	2734.34		0.16	1713294.32	4652.82		0.27	0.98
96	1694112.52	4449.69		0.26	1714438.36	5621.66		0.33	1.01
104	1780279.76	2420.52		0.14	1767679.12	3067.66		0.17	0.99
112	1700284.72	9796.23		0.58	1796674.6	4066.06		0.23	1.06
120	1760466.72	3978.65		0.23	1704706.08	4080.04		0.24	0.97
128	1634067.96	5187.94		0.32	1764115.48	3545.02		0.2	1.08
136	1170303.84	7602.29		0.65	1227188.04	8090.84		0.66	1.05
144	953186.16	7859.02		0.82	964822.08	10536.61	1.09	1.01
152	818893.96	7238.86		0.88	853412.44	5932.25		0.7	1.04
160	707460.48	3868.26		0.55	746985.68	10363.03	1.39	1.06
168	658380.56	4938.77		0.75	672101.12	5442.95		0.81	1.02
176	614692.04	3137.74		0.51	615143.36	6197.19		1.01	1
184	574808.88	4741.61		0.82	592395.08	8840.92		1.49	1.03
192	548142.92	6116.31		1.12	571299.68	8388.56		1.47	1.04
200	511621.96	2182.33		0.43	532144.88	5467.04		1.03	1.04
208	506583.32	6834.39		1.35	521427.08	10318.65	1.98	1.03
216	480438.04	3608.96		0.75	510697.76	8086.47		1.58	1.06
224	470644.96	3451.35		0.73	467433.92	5008.59		1.07	0.99
232	466973.72	6599.97		1.41	444345.92	2144.96		0.48	0.95
240	442927.68	2351.56		0.53	440503.56	4289.01		0.97	0.99
248	432991.16	5829.92		1.35	445462.6	5944.03		1.33	1.03
256	409455.44	1430.5		0.35	422219.4	4007.04		0.95	1.03

will-it-scale open2_threads - arm64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	818645.4	1097.02		0.13	774110.24	1562.45		0.2	0.95
2	1281013.04	2188.78		0.17	1238346.24	2149.97		0.17	0.97
4	2058514.16	13105.36	0.64	1985375		3204.48		0.16	0.96
8	1920414.8	16154.63	0.84	1911667.92	8882.98		0.46	1
16	1943729.68	8714.38		0.45	1978946.72	7465.65		0.38	1.02
24	1915846.88	7749.9		0.4	1914442.72	9841.71		0.51	1
32	1964695.92	8854.83		0.45	1914650.28	9357.82		0.49	0.97
40	1845071.12	5103.26		0.28	1891685.44	4278.34		0.23	1.03
48	1838897.6	5123.61		0.28	1843498.2	5391.94		0.29	1
56	1823768.32	3214.14		0.18	1736477.48	5675.49		0.33	0.95
64	1627162.36	3528.1		0.22	1685727.16	6102.63		0.36	1.04
72	1725320.16	4709.83		0.27	1710174.4	6707.54		0.39	0.99
80	1692288.44	9110.89		0.54	1773676.24	4327.94		0.24	1.05
88	1725496.64	4249.71		0.25	1695173.84	5097.14		0.3	0.98
96	1766093.08	2280.09		0.13	1732782.64	3606.1		0.21	0.98
104	1647753		2926.83		0.18	1710876.4	4416.04		0.26	1.04
112	1763785.52	3838.26		0.22	1803813.76	1859.2		0.1	1.02
120	1684095.16	2385.31		0.14	1766903.08	3258.34		0.18	1.05
128	1733528.56	2800.62		0.16	1677446.32	3201.14		0.19	0.97
136	1179187.84	6804.86		0.58	1241839.52	10698.51	0.86	1.05
144	969456.36	6421.85		0.66	1018441.96	8732.19		0.86	1.05
152	839295.64	10422.66	1.24	817531.92	6778.37		0.83	0.97
160	743010.72	6957.98		0.94	749291.16	9388.47		1.25	1.01
168	666049.88	13159.73	1.98	689408.08	10192.66	1.48	1.04
176	609185.56	5685.18		0.93	653744.24	10847.35	1.66	1.07
184	602232.08	12089.72	2.01	597718.6	13856.45	2.32	0.99
192	563919.32	9870.46		1.75	560080.4	8388.47		1.5	0.99
200	522396.28	4155.61		0.8	539168.64	10456.64	1.94	1.03
208	520328.28	9353.14		1.8	510011.4	6061.19		1.19	0.98
216	479797.72	5824.58		1.21	486955.32	4547.05		0.93	1.01
224	467943.8	4484.86		0.96	473252.76	5608.58		1.19	1.01
232	456914.24	3129.5		0.68	457463.2	7474.83		1.63	1
240	450535		5149.78		1.14	437653.56	4604.92		1.05	0.97
248	435475.2	2350.87		0.54	435589.24	6176.01		1.42	1
256	416737.88	2592.76		0.62	424178.28	3932.2		0.93	1.02

will-it-scale lock1_threads - arm64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	2512077.52	3026.1		0.12	2085365.92	1612.44		0.08	0.83
2	4840180.4	3646.31		0.08	4326922.24	3802.17		0.09	0.89
4	9358779.44	6673.07		0.07	8467588.56	5577.05		0.07	0.9
8	9374436.88	18826.26	0.2	8635110.16	4217.66		0.05	0.92
16	9527184.08	14111.94	0.15	8561174.16	3258.6		0.04	0.9
24	8873099.76	17242.32	0.19	9286778.72	4124.51		0.04	1.05
32	8457640.4	10790.92	0.13	8700401.52	5110		0.06	1.03
40	8478771.76	13250.8		0.16	8746198.16	7606.42		0.09	1.03
48	8329097.76	7958.92		0.1	8774265.36	6082.08		0.07	1.05
56	8330143.04	11586.93	0.14	8472426.48	7402.13		0.09	1.02
64	8334684.08	10478.03	0.13	7979193.52	8436.63		0.11	0.96
72	7941815.52	16031.38	0.2	8016885.52	12640.56	0.16	1.01
80	8042221.68	10219.93	0.13	8072222.88	12479.54	0.15	1
88	8190336.8	10751.38	0.13	8432977.6	11865.67	0.14	1.03
96	8235010.08	7267.8		0.09	8022101.28	11910.63	0.15	0.97
104	8154434.08	7770.8		0.1	7987812		7647.42		0.1	0.98
112	7738464.56	11067.72	0.14	7968483.92	20632.93	0.26	1.03
120	8228919.36	10395.79	0.13	8304329.28	11913.76	0.14	1.01
128	7798646.64	8877.8		0.11	8197938.4	7527.81		0.09	1.05
136	5567293.68	66259.82	1.19	5642017.12	126584.59	2.24	1.01
144	4425655.52	55729.96	1.26	4519874.64	82996.01	1.84	1.02
152	3871300.8	77793.78	2.01	3850025.04	80167.3		2.08	0.99
160	3558041.68	55108.3		1.55	3495924.96	83626.42	2.39	0.98
168	3302042.72	45011.89	1.36	3298002.8	59393.64	1.8	1
176	3066165.2	34896.54	1.14	3063027.44	58219.26	1.9	1
184	2817899.6	43585.27	1.55	2859393.84	45258.03	1.58	1.01
192	2690403.76	42236.77	1.57	2630652.24	35953.13	1.37	0.98
200	2563141.44	28145.43	1.1	2539964.32	38556.52	1.52	0.99
208	2502968.8	27687.81	1.11	2477757.28	28240.81	1.14	0.99
216	2474917.76	24128.71	0.97	2483161.44	32198.37	1.3	1
224	2386874.72	32954.66	1.38	2398068.48	37667.29	1.57	1
232	2379248.24	27413.4		1.15	2327601.68	24565.28	1.06	0.98
240	2302146.64	19914.19	0.87	2236074.64	20968.17	0.94	0.97
248	2241798.32	21542.52	0.96	2173312.24	26498.36	1.22	0.97
256	2198765.12	20832.66	0.95	2136159.52	25027.96	1.17	0.97

will-it-scale lock2_threads - arm64

Threads QL      	QL stddev       stddev% RQL     	RQL stddev      stddev% Speedup
-----------------------------------------------------------------------------------------------
1	2499414.32	1932.27		0.08	2075704.8	24589.71	1.18	0.83
2	3887820		34198.36	0.88	4057432.64	11896.04	0.29	1.04
4	3445307.6	7958.3		0.23	3869960.4	3788.5		0.1	1.12
8	4310597.2	14405.9		0.33	3931319.76	5845.33		0.15	0.91
16	3995159.84	22621.85	0.57	3953339.68	15668.9		0.4	0.99
24	4048456.88	22956.51	0.57	3887812.64	30584.77	0.79	0.96
32	3974808.64	20465.87	0.51	3718778.08	27407.24	0.74	0.94
40	3941154.88	15136.68	0.38	3551464.24	33378.67	0.94	0.9
48	3725436.32	17090.67	0.46	3714356.08	19035.26	0.51	1
56	3558449.44	10123.46	0.28	3449656.08	36476.87	1.06	0.97
64	3514616.08	16470.99	0.47	3493197.04	25639.82	0.73	0.99
72	3461700.88	16780.97	0.48	3376565.04	16930.19	0.5	0.98
80	3797008.64	17599.05	0.46	3505856.16	34320.34	0.98	0.92
88	3737459.44	10774.93	0.29	3631757.68	24231.29	0.67	0.97
96	3612816.16	21865.86	0.61	3545354.56	16391.15	0.46	0.98
104	3765167.36	17763.8		0.47	3466467.12	22235.45	0.64	0.92
112	3713386		15455.21	0.42	3402210		18349.66	0.54	0.92
120	3699986.08	15153.08	0.41	3580303.92	19823.01	0.55	0.97
128	3648694.56	11891.62	0.33	3426445.28	22993.32	0.67	0.94
136	800046.88	6039.73		0.75	784412.16	9062.03		1.16	0.98
144	769483.36	5231.74		0.68	714132.8	8953.57		1.25	0.93
152	821081.52	4249.12		0.52	743694.64	8155.18		1.1	0.91
160	789040.16	9187.4		1.16	834865.44	6159.29		0.74	1.06
168	867742.4	8967.66		1.03	734905.36	15582.75	2.12	0.85
176	838650.32	7949.72		0.95	846939.68	8959.8		1.06	1.01
184	854984.48	19475.51	2.28	794549.92	11924.54	1.5	0.93
192	846262.32	13795.86	1.63	899915.12	8639.82		0.96	1.06
200	942602.16	12665.42	1.34	900385.76	8592.23		0.95	0.96
208	954183.68	12853.22	1.35	1166186.96	13045.03	1.12	1.22
216	929319.76	10157.79	1.09	926773.76	10577.01	1.14	1
224	967896.56	9819.6		1.01	951144.32	12343.83	1.3	0.98
232	990621.12	7771.97		0.78	916361.2	17878.44	1.95	0.93
240	995285.04	20104.22	2.02	972119.6	12856.42	1.32	0.98
248	1029436		20404.97	1.98	965301.28	11102.95	1.15	0.94
256	1038724.8	19201.03	1.85	1029942.08	12563.07	1.22	0.99

Written By
----------
Alexei Starovoitov <ast@kernel.org>
Kumar Kartikeya Dwivedi <memxor@gmail.com>

  [0]: https://www.cs.rochester.edu/research/synchronization/pseudocode/timeout.html
  [1]: https://dl.acm.org/doi/10.1145/571825.571830
  [2]: https://github.com/kkdwivedi/rqspinlock/blob/main/rqspinlock.pdf
  [3]: https://git.kernel.org/pub/scm/linux/kernel/git/cmarinas/kernel-tla.git/plain/qspinlock.tla
  [4]: https://arxiv.org/pdf/1810.05600

Kumar Kartikeya Dwivedi (25):
  locking: Move MCS struct definition to public header
  locking: Move common qspinlock helpers to a private header
  locking: Allow obtaining result of arch_mcs_spin_lock_contended
  locking: Copy out qspinlock.c to kernel/bpf/rqspinlock.c
  rqspinlock: Add rqspinlock.h header
  rqspinlock: Drop PV and virtualization support
  rqspinlock: Add support for timeouts
  rqspinlock: Hardcode cond_acquire loops for arm64
  rqspinlock: Protect pending bit owners from stalls
  rqspinlock: Protect waiters in queue from stalls
  rqspinlock: Protect waiters in trylock fallback from stalls
  rqspinlock: Add deadlock detection and recovery
  rqspinlock: Add a test-and-set fallback
  rqspinlock: Add basic support for CONFIG_PARAVIRT
  rqspinlock: Add helper to print a splat on timeout or deadlock
  rqspinlock: Add macros for rqspinlock usage
  rqspinlock: Add entry to Makefile, MAINTAINERS
  rqspinlock: Add locktorture support
  bpf: Convert hashtab.c to rqspinlock
  bpf: Convert percpu_freelist.c to rqspinlock
  bpf: Convert lpm_trie.c to rqspinlock
  bpf: Introduce rqspinlock kfuncs
  bpf: Implement verifier support for rqspinlock
  bpf: Maintain FIFO property for rqspinlock unlock
  selftests/bpf: Add tests for rqspinlock

 MAINTAINERS                                   |   2 +
 arch/arm64/include/asm/rqspinlock.h           |  93 +++
 arch/x86/include/asm/rqspinlock.h             |  33 +
 include/asm-generic/Kbuild                    |   1 +
 include/asm-generic/mcs_spinlock.h            |   6 +
 include/asm-generic/rqspinlock.h              | 250 ++++++
 include/linux/bpf.h                           |  10 +
 include/linux/bpf_verifier.h                  |  19 +-
 kernel/bpf/Makefile                           |   2 +-
 kernel/bpf/btf.c                              |  26 +-
 kernel/bpf/hashtab.c                          | 102 +--
 kernel/bpf/lpm_trie.c                         |  25 +-
 kernel/bpf/percpu_freelist.c                  | 113 +--
 kernel/bpf/percpu_freelist.h                  |   4 +-
 kernel/bpf/rqspinlock.c                       | 770 ++++++++++++++++++
 kernel/bpf/rqspinlock.h                       |  48 ++
 kernel/bpf/syscall.c                          |   6 +-
 kernel/bpf/verifier.c                         | 248 +++++-
 kernel/locking/lock_events_list.h             |   5 +
 kernel/locking/locktorture.c                  |  57 ++
 kernel/locking/mcs_spinlock.h                 |  10 +-
 kernel/locking/qspinlock.c                    | 193 +----
 kernel/locking/qspinlock.h                    | 200 +++++
 .../selftests/bpf/prog_tests/res_spin_lock.c  |  98 +++
 tools/testing/selftests/bpf/progs/irq.c       |  53 ++
 .../selftests/bpf/progs/res_spin_lock.c       | 143 ++++
 .../selftests/bpf/progs/res_spin_lock_fail.c  | 244 ++++++
 27 files changed, 2344 insertions(+), 417 deletions(-)
 create mode 100644 arch/arm64/include/asm/rqspinlock.h
 create mode 100644 arch/x86/include/asm/rqspinlock.h
 create mode 100644 include/asm-generic/rqspinlock.h
 create mode 100644 kernel/bpf/rqspinlock.c
 create mode 100644 kernel/bpf/rqspinlock.h
 create mode 100644 kernel/locking/qspinlock.h
 create mode 100644 tools/testing/selftests/bpf/prog_tests/res_spin_lock.c
 create mode 100644 tools/testing/selftests/bpf/progs/res_spin_lock.c
 create mode 100644 tools/testing/selftests/bpf/progs/res_spin_lock_fail.c


base-commit: 812f7702d83d84cdf776d75e2ba5386de9e8acc0
-- 
2.47.1

[PATCH bpf-next v4 01/25] locking: Move MCS struct definition to public header

[Kumar Kartikeya Dwivedi]

Move the definition of the struct mcs_spinlock from the private
mcs_spinlock.h header in kernel/locking to the mcs_spinlock.h
asm-generic header, since we will need to reference it from the
qspinlock.h header in subsequent commits.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/mcs_spinlock.h | 6 ++++++
 kernel/locking/mcs_spinlock.h      | 6 ------
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/mcs_spinlock.h b/include/asm-generic/mcs_spinlock.h
index 10cd4ffc6ba2..39c94012b88a 100644
--- a/include/asm-generic/mcs_spinlock.h
+++ b/include/asm-generic/mcs_spinlock.h
@@ -1,6 +1,12 @@
 #ifndef __ASM_MCS_SPINLOCK_H
 #define __ASM_MCS_SPINLOCK_H
 
+struct mcs_spinlock {
+	struct mcs_spinlock *next;
+	int locked; /* 1 if lock acquired */
+	int count;  /* nesting count, see qspinlock.c */
+};
+
 /*
  * Architectures can define their own:
  *
diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index 85251d8771d9..16160ca8907f 100644
--- a/kernel/locking/mcs_spinlock.h
+++ b/kernel/locking/mcs_spinlock.h
@@ -15,12 +15,6 @@
 
 #include <asm/mcs_spinlock.h>
 
-struct mcs_spinlock {
-	struct mcs_spinlock *next;
-	int locked; /* 1 if lock acquired */
-	int count;  /* nesting count, see qspinlock.c */
-};
-
 #ifndef arch_mcs_spin_lock_contended
 /*
  * Using smp_cond_load_acquire() provides the acquire semantics
-- 
2.47.1

[PATCH bpf-next v4 02/25] locking: Move common qspinlock helpers to a private header

[Kumar Kartikeya Dwivedi]

Move qspinlock helper functions that encode, decode tail word, set and
clear the pending and locked bits, and other miscellaneous definitions
and macros to a private header. To this end, create a qspinlock.h header
file in kernel/locking. Subsequent commits will introduce a modified
qspinlock slow path function, thus moving shared code to a private
header will help minimize unnecessary code duplication.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/locking/qspinlock.c | 193 +----------------------------------
 kernel/locking/qspinlock.h | 200 +++++++++++++++++++++++++++++++++++++
 2 files changed, 205 insertions(+), 188 deletions(-)
 create mode 100644 kernel/locking/qspinlock.h

diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 7d96bed718e4..af8d122bb649 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -25,8 +25,9 @@
 #include <trace/events/lock.h>
 
 /*
- * Include queued spinlock statistics code
+ * Include queued spinlock definitions and statistics code
  */
+#include "qspinlock.h"
 #include "qspinlock_stat.h"
 
 /*
@@ -67,36 +68,6 @@
  */
 
 #include "mcs_spinlock.h"
-#define MAX_NODES	4
-
-/*
- * On 64-bit architectures, the mcs_spinlock structure will be 16 bytes in
- * size and four of them will fit nicely in one 64-byte cacheline. For
- * pvqspinlock, however, we need more space for extra data. To accommodate
- * that, we insert two more long words to pad it up to 32 bytes. IOW, only
- * two of them can fit in a cacheline in this case. That is OK as it is rare
- * to have more than 2 levels of slowpath nesting in actual use. We don't
- * want to penalize pvqspinlocks to optimize for a rare case in native
- * qspinlocks.
- */
-struct qnode {
-	struct mcs_spinlock mcs;
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-	long reserved[2];
-#endif
-};
-
-/*
- * The pending bit spinning loop count.
- * This heuristic is used to limit the number of lockword accesses
- * made by atomic_cond_read_relaxed when waiting for the lock to
- * transition out of the "== _Q_PENDING_VAL" state. We don't spin
- * indefinitely because there's no guarantee that we'll make forward
- * progress.
- */
-#ifndef _Q_PENDING_LOOPS
-#define _Q_PENDING_LOOPS	1
-#endif
 
 /*
  * Per-CPU queue node structures; we can never have more than 4 nested
@@ -106,161 +77,7 @@ struct qnode {
  *
  * PV doubles the storage and uses the second cacheline for PV state.
  */
-static DEFINE_PER_CPU_ALIGNED(struct qnode, qnodes[MAX_NODES]);
-
-/*
- * We must be able to distinguish between no-tail and the tail at 0:0,
- * therefore increment the cpu number by one.
- */
-
-static inline __pure u32 encode_tail(int cpu, int idx)
-{
-	u32 tail;
-
-	tail  = (cpu + 1) << _Q_TAIL_CPU_OFFSET;
-	tail |= idx << _Q_TAIL_IDX_OFFSET; /* assume < 4 */
-
-	return tail;
-}
-
-static inline __pure struct mcs_spinlock *decode_tail(u32 tail)
-{
-	int cpu = (tail >> _Q_TAIL_CPU_OFFSET) - 1;
-	int idx = (tail &  _Q_TAIL_IDX_MASK) >> _Q_TAIL_IDX_OFFSET;
-
-	return per_cpu_ptr(&qnodes[idx].mcs, cpu);
-}
-
-static inline __pure
-struct mcs_spinlock *grab_mcs_node(struct mcs_spinlock *base, int idx)
-{
-	return &((struct qnode *)base + idx)->mcs;
-}
-
-#define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK)
-
-#if _Q_PENDING_BITS == 8
-/**
- * clear_pending - clear the pending bit.
- * @lock: Pointer to queued spinlock structure
- *
- * *,1,* -> *,0,*
- */
-static __always_inline void clear_pending(struct qspinlock *lock)
-{
-	WRITE_ONCE(lock->pending, 0);
-}
-
-/**
- * clear_pending_set_locked - take ownership and clear the pending bit.
- * @lock: Pointer to queued spinlock structure
- *
- * *,1,0 -> *,0,1
- *
- * Lock stealing is not allowed if this function is used.
- */
-static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
-{
-	WRITE_ONCE(lock->locked_pending, _Q_LOCKED_VAL);
-}
-
-/*
- * xchg_tail - Put in the new queue tail code word & retrieve previous one
- * @lock : Pointer to queued spinlock structure
- * @tail : The new queue tail code word
- * Return: The previous queue tail code word
- *
- * xchg(lock, tail), which heads an address dependency
- *
- * p,*,* -> n,*,* ; prev = xchg(lock, node)
- */
-static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
-{
-	/*
-	 * We can use relaxed semantics since the caller ensures that the
-	 * MCS node is properly initialized before updating the tail.
-	 */
-	return (u32)xchg_relaxed(&lock->tail,
-				 tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;
-}
-
-#else /* _Q_PENDING_BITS == 8 */
-
-/**
- * clear_pending - clear the pending bit.
- * @lock: Pointer to queued spinlock structure
- *
- * *,1,* -> *,0,*
- */
-static __always_inline void clear_pending(struct qspinlock *lock)
-{
-	atomic_andnot(_Q_PENDING_VAL, &lock->val);
-}
-
-/**
- * clear_pending_set_locked - take ownership and clear the pending bit.
- * @lock: Pointer to queued spinlock structure
- *
- * *,1,0 -> *,0,1
- */
-static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
-{
-	atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val);
-}
-
-/**
- * xchg_tail - Put in the new queue tail code word & retrieve previous one
- * @lock : Pointer to queued spinlock structure
- * @tail : The new queue tail code word
- * Return: The previous queue tail code word
- *
- * xchg(lock, tail)
- *
- * p,*,* -> n,*,* ; prev = xchg(lock, node)
- */
-static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
-{
-	u32 old, new;
-
-	old = atomic_read(&lock->val);
-	do {
-		new = (old & _Q_LOCKED_PENDING_MASK) | tail;
-		/*
-		 * We can use relaxed semantics since the caller ensures that
-		 * the MCS node is properly initialized before updating the
-		 * tail.
-		 */
-	} while (!atomic_try_cmpxchg_relaxed(&lock->val, &old, new));
-
-	return old;
-}
-#endif /* _Q_PENDING_BITS == 8 */
-
-/**
- * queued_fetch_set_pending_acquire - fetch the whole lock value and set pending
- * @lock : Pointer to queued spinlock structure
- * Return: The previous lock value
- *
- * *,*,* -> *,1,*
- */
-#ifndef queued_fetch_set_pending_acquire
-static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lock)
-{
-	return atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val);
-}
-#endif
-
-/**
- * set_locked - Set the lock bit and own the lock
- * @lock: Pointer to queued spinlock structure
- *
- * *,*,0 -> *,0,1
- */
-static __always_inline void set_locked(struct qspinlock *lock)
-{
-	WRITE_ONCE(lock->locked, _Q_LOCKED_VAL);
-}
-
+static DEFINE_PER_CPU_ALIGNED(struct qnode, qnodes[_Q_MAX_NODES]);
 
 /*
  * Generate the native code for queued_spin_unlock_slowpath(); provide NOPs for
@@ -410,7 +227,7 @@ void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 	 * any MCS node. This is not the most elegant solution, but is
 	 * simple enough.
 	 */
-	if (unlikely(idx >= MAX_NODES)) {
+	if (unlikely(idx >= _Q_MAX_NODES)) {
 		lockevent_inc(lock_no_node);
 		while (!queued_spin_trylock(lock))
 			cpu_relax();
@@ -465,7 +282,7 @@ void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 	 * head of the waitqueue.
 	 */
 	if (old & _Q_TAIL_MASK) {
-		prev = decode_tail(old);
+		prev = decode_tail(old, qnodes);
 
 		/* Link @node into the waitqueue. */
 		WRITE_ONCE(prev->next, node);
diff --git a/kernel/locking/qspinlock.h b/kernel/locking/qspinlock.h
new file mode 100644
index 000000000000..d4ceb9490365
--- /dev/null
+++ b/kernel/locking/qspinlock.h
@@ -0,0 +1,200 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Queued spinlock defines
+ *
+ * This file contains macro definitions and functions shared between different
+ * qspinlock slow path implementations.
+ */
+#ifndef __LINUX_QSPINLOCK_H
+#define __LINUX_QSPINLOCK_H
+
+#include <asm-generic/percpu.h>
+#include <linux/percpu-defs.h>
+#include <asm-generic/qspinlock.h>
+#include <asm-generic/mcs_spinlock.h>
+
+#define _Q_MAX_NODES	4
+
+/*
+ * The pending bit spinning loop count.
+ * This heuristic is used to limit the number of lockword accesses
+ * made by atomic_cond_read_relaxed when waiting for the lock to
+ * transition out of the "== _Q_PENDING_VAL" state. We don't spin
+ * indefinitely because there's no guarantee that we'll make forward
+ * progress.
+ */
+#ifndef _Q_PENDING_LOOPS
+#define _Q_PENDING_LOOPS	1
+#endif
+
+/*
+ * On 64-bit architectures, the mcs_spinlock structure will be 16 bytes in
+ * size and four of them will fit nicely in one 64-byte cacheline. For
+ * pvqspinlock, however, we need more space for extra data. To accommodate
+ * that, we insert two more long words to pad it up to 32 bytes. IOW, only
+ * two of them can fit in a cacheline in this case. That is OK as it is rare
+ * to have more than 2 levels of slowpath nesting in actual use. We don't
+ * want to penalize pvqspinlocks to optimize for a rare case in native
+ * qspinlocks.
+ */
+struct qnode {
+	struct mcs_spinlock mcs;
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+	long reserved[2];
+#endif
+};
+
+/*
+ * We must be able to distinguish between no-tail and the tail at 0:0,
+ * therefore increment the cpu number by one.
+ */
+
+static inline __pure u32 encode_tail(int cpu, int idx)
+{
+	u32 tail;
+
+	tail  = (cpu + 1) << _Q_TAIL_CPU_OFFSET;
+	tail |= idx << _Q_TAIL_IDX_OFFSET; /* assume < 4 */
+
+	return tail;
+}
+
+static inline __pure struct mcs_spinlock *decode_tail(u32 tail, struct qnode *qnodes)
+{
+	int cpu = (tail >> _Q_TAIL_CPU_OFFSET) - 1;
+	int idx = (tail &  _Q_TAIL_IDX_MASK) >> _Q_TAIL_IDX_OFFSET;
+
+	return per_cpu_ptr(&qnodes[idx].mcs, cpu);
+}
+
+static inline __pure
+struct mcs_spinlock *grab_mcs_node(struct mcs_spinlock *base, int idx)
+{
+	return &((struct qnode *)base + idx)->mcs;
+}
+
+#define _Q_LOCKED_PENDING_MASK (_Q_LOCKED_MASK | _Q_PENDING_MASK)
+
+#if _Q_PENDING_BITS == 8
+/**
+ * clear_pending - clear the pending bit.
+ * @lock: Pointer to queued spinlock structure
+ *
+ * *,1,* -> *,0,*
+ */
+static __always_inline void clear_pending(struct qspinlock *lock)
+{
+	WRITE_ONCE(lock->pending, 0);
+}
+
+/**
+ * clear_pending_set_locked - take ownership and clear the pending bit.
+ * @lock: Pointer to queued spinlock structure
+ *
+ * *,1,0 -> *,0,1
+ *
+ * Lock stealing is not allowed if this function is used.
+ */
+static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
+{
+	WRITE_ONCE(lock->locked_pending, _Q_LOCKED_VAL);
+}
+
+/*
+ * xchg_tail - Put in the new queue tail code word & retrieve previous one
+ * @lock : Pointer to queued spinlock structure
+ * @tail : The new queue tail code word
+ * Return: The previous queue tail code word
+ *
+ * xchg(lock, tail), which heads an address dependency
+ *
+ * p,*,* -> n,*,* ; prev = xchg(lock, node)
+ */
+static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
+{
+	/*
+	 * We can use relaxed semantics since the caller ensures that the
+	 * MCS node is properly initialized before updating the tail.
+	 */
+	return (u32)xchg_relaxed(&lock->tail,
+				 tail >> _Q_TAIL_OFFSET) << _Q_TAIL_OFFSET;
+}
+
+#else /* _Q_PENDING_BITS == 8 */
+
+/**
+ * clear_pending - clear the pending bit.
+ * @lock: Pointer to queued spinlock structure
+ *
+ * *,1,* -> *,0,*
+ */
+static __always_inline void clear_pending(struct qspinlock *lock)
+{
+	atomic_andnot(_Q_PENDING_VAL, &lock->val);
+}
+
+/**
+ * clear_pending_set_locked - take ownership and clear the pending bit.
+ * @lock: Pointer to queued spinlock structure
+ *
+ * *,1,0 -> *,0,1
+ */
+static __always_inline void clear_pending_set_locked(struct qspinlock *lock)
+{
+	atomic_add(-_Q_PENDING_VAL + _Q_LOCKED_VAL, &lock->val);
+}
+
+/**
+ * xchg_tail - Put in the new queue tail code word & retrieve previous one
+ * @lock : Pointer to queued spinlock structure
+ * @tail : The new queue tail code word
+ * Return: The previous queue tail code word
+ *
+ * xchg(lock, tail)
+ *
+ * p,*,* -> n,*,* ; prev = xchg(lock, node)
+ */
+static __always_inline u32 xchg_tail(struct qspinlock *lock, u32 tail)
+{
+	u32 old, new;
+
+	old = atomic_read(&lock->val);
+	do {
+		new = (old & _Q_LOCKED_PENDING_MASK) | tail;
+		/*
+		 * We can use relaxed semantics since the caller ensures that
+		 * the MCS node is properly initialized before updating the
+		 * tail.
+		 */
+	} while (!atomic_try_cmpxchg_relaxed(&lock->val, &old, new));
+
+	return old;
+}
+#endif /* _Q_PENDING_BITS == 8 */
+
+/**
+ * queued_fetch_set_pending_acquire - fetch the whole lock value and set pending
+ * @lock : Pointer to queued spinlock structure
+ * Return: The previous lock value
+ *
+ * *,*,* -> *,1,*
+ */
+#ifndef queued_fetch_set_pending_acquire
+static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lock)
+{
+	return atomic_fetch_or_acquire(_Q_PENDING_VAL, &lock->val);
+}
+#endif
+
+/**
+ * set_locked - Set the lock bit and own the lock
+ * @lock: Pointer to queued spinlock structure
+ *
+ * *,*,0 -> *,0,1
+ */
+static __always_inline void set_locked(struct qspinlock *lock)
+{
+	WRITE_ONCE(lock->locked, _Q_LOCKED_VAL);
+}
+
+#endif /* __LINUX_QSPINLOCK_H */
-- 
2.47.1

[PATCH bpf-next v4 03/25] locking: Allow obtaining result of arch_mcs_spin_lock_contended

[Kumar Kartikeya Dwivedi]

To support upcoming changes that require inspecting the return value
once the conditional waiting loop in arch_mcs_spin_lock_contended
terminates, modify the macro to preserve the result of
smp_cond_load_acquire. This enables checking the return value as needed,
which will help disambiguate the MCS node’s locked state in future
patches.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/locking/mcs_spinlock.h | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h
index 16160ca8907f..5c92ba199b90 100644
--- a/kernel/locking/mcs_spinlock.h
+++ b/kernel/locking/mcs_spinlock.h
@@ -24,9 +24,7 @@
  * spinning, and smp_cond_load_acquire() provides that behavior.
  */
 #define arch_mcs_spin_lock_contended(l)					\
-do {									\
-	smp_cond_load_acquire(l, VAL);					\
-} while (0)
+	smp_cond_load_acquire(l, VAL)
 #endif
 
 #ifndef arch_mcs_spin_unlock_contended
-- 
2.47.1

[PATCH bpf-next v4 04/25] locking: Copy out qspinlock.c to kernel/bpf/rqspinlock.c

[Kumar Kartikeya Dwivedi]

In preparation for introducing a new lock implementation, Resilient
Queued Spin Lock, or rqspinlock, we first begin our modifications by
using the existing qspinlock.c code as the base. Simply copy the code to
a new file and rename functions and variables from 'queued' to
'resilient_queued'.

Since we place the file in kernel/bpf, include needs to be relative.

This helps each subsequent commit in clearly showing how and where the
code is being changed. The only change after a literal copy in this
commit is renaming the functions where necessary, and rename qnodes to
rqnodes. Let's also use EXPORT_SYMBOL_GPL for rqspinlock slowpath.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/rqspinlock.c | 410 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 410 insertions(+)
 create mode 100644 kernel/bpf/rqspinlock.c

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
new file mode 100644
index 000000000000..762108cb0f38
--- /dev/null
+++ b/kernel/bpf/rqspinlock.c
@@ -0,0 +1,410 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Resilient Queued Spin Lock
+ *
+ * (C) Copyright 2013-2015 Hewlett-Packard Development Company, L.P.
+ * (C) Copyright 2013-2014,2018 Red Hat, Inc.
+ * (C) Copyright 2015 Intel Corp.
+ * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
+ *
+ * Authors: Waiman Long <longman@redhat.com>
+ *          Peter Zijlstra <peterz@infradead.org>
+ */
+
+#ifndef _GEN_PV_LOCK_SLOWPATH
+
+#include <linux/smp.h>
+#include <linux/bug.h>
+#include <linux/cpumask.h>
+#include <linux/percpu.h>
+#include <linux/hardirq.h>
+#include <linux/mutex.h>
+#include <linux/prefetch.h>
+#include <asm/byteorder.h>
+#include <asm/qspinlock.h>
+#include <trace/events/lock.h>
+
+/*
+ * Include queued spinlock definitions and statistics code
+ */
+#include "../locking/qspinlock.h"
+#include "../locking/qspinlock_stat.h"
+
+/*
+ * The basic principle of a queue-based spinlock can best be understood
+ * by studying a classic queue-based spinlock implementation called the
+ * MCS lock. A copy of the original MCS lock paper ("Algorithms for Scalable
+ * Synchronization on Shared-Memory Multiprocessors by Mellor-Crummey and
+ * Scott") is available at
+ *
+ * https://bugzilla.kernel.org/show_bug.cgi?id=206115
+ *
+ * This queued spinlock implementation is based on the MCS lock, however to
+ * make it fit the 4 bytes we assume spinlock_t to be, and preserve its
+ * existing API, we must modify it somehow.
+ *
+ * In particular; where the traditional MCS lock consists of a tail pointer
+ * (8 bytes) and needs the next pointer (another 8 bytes) of its own node to
+ * unlock the next pending (next->locked), we compress both these: {tail,
+ * next->locked} into a single u32 value.
+ *
+ * Since a spinlock disables recursion of its own context and there is a limit
+ * to the contexts that can nest; namely: task, softirq, hardirq, nmi. As there
+ * are at most 4 nesting levels, it can be encoded by a 2-bit number. Now
+ * we can encode the tail by combining the 2-bit nesting level with the cpu
+ * number. With one byte for the lock value and 3 bytes for the tail, only a
+ * 32-bit word is now needed. Even though we only need 1 bit for the lock,
+ * we extend it to a full byte to achieve better performance for architectures
+ * that support atomic byte write.
+ *
+ * We also change the first spinner to spin on the lock bit instead of its
+ * node; whereby avoiding the need to carry a node from lock to unlock, and
+ * preserving existing lock API. This also makes the unlock code simpler and
+ * faster.
+ *
+ * N.B. The current implementation only supports architectures that allow
+ *      atomic operations on smaller 8-bit and 16-bit data types.
+ *
+ */
+
+#include "../locking/mcs_spinlock.h"
+
+/*
+ * Per-CPU queue node structures; we can never have more than 4 nested
+ * contexts: task, softirq, hardirq, nmi.
+ *
+ * Exactly fits one 64-byte cacheline on a 64-bit architecture.
+ *
+ * PV doubles the storage and uses the second cacheline for PV state.
+ */
+static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
+
+/*
+ * Generate the native code for resilient_queued_spin_unlock_slowpath(); provide NOPs
+ * for all the PV callbacks.
+ */
+
+static __always_inline void __pv_init_node(struct mcs_spinlock *node) { }
+static __always_inline void __pv_wait_node(struct mcs_spinlock *node,
+					   struct mcs_spinlock *prev) { }
+static __always_inline void __pv_kick_node(struct qspinlock *lock,
+					   struct mcs_spinlock *node) { }
+static __always_inline u32  __pv_wait_head_or_lock(struct qspinlock *lock,
+						   struct mcs_spinlock *node)
+						   { return 0; }
+
+#define pv_enabled()		false
+
+#define pv_init_node		__pv_init_node
+#define pv_wait_node		__pv_wait_node
+#define pv_kick_node		__pv_kick_node
+#define pv_wait_head_or_lock	__pv_wait_head_or_lock
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#define resilient_queued_spin_lock_slowpath	native_resilient_queued_spin_lock_slowpath
+#endif
+
+#endif /* _GEN_PV_LOCK_SLOWPATH */
+
+/**
+ * resilient_queued_spin_lock_slowpath - acquire the queued spinlock
+ * @lock: Pointer to queued spinlock structure
+ * @val: Current value of the queued spinlock 32-bit word
+ *
+ * (queue tail, pending bit, lock value)
+ *
+ *              fast     :    slow                                  :    unlock
+ *                       :                                          :
+ * uncontended  (0,0,0) -:--> (0,0,1) ------------------------------:--> (*,*,0)
+ *                       :       | ^--------.------.             /  :
+ *                       :       v           \      \            |  :
+ * pending               :    (0,1,1) +--> (0,1,0)   \           |  :
+ *                       :       | ^--'              |           |  :
+ *                       :       v                   |           |  :
+ * uncontended           :    (n,x,y) +--> (n,0,0) --'           |  :
+ *   queue               :       | ^--'                          |  :
+ *                       :       v                               |  :
+ * contended             :    (*,x,y) +--> (*,0,0) ---> (*,0,1) -'  :
+ *   queue               :         ^--'                             :
+ */
+void __lockfunc resilient_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
+{
+	struct mcs_spinlock *prev, *next, *node;
+	u32 old, tail;
+	int idx;
+
+	BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));
+
+	if (pv_enabled())
+		goto pv_queue;
+
+	if (virt_spin_lock(lock))
+		return;
+
+	/*
+	 * Wait for in-progress pending->locked hand-overs with a bounded
+	 * number of spins so that we guarantee forward progress.
+	 *
+	 * 0,1,0 -> 0,0,1
+	 */
+	if (val == _Q_PENDING_VAL) {
+		int cnt = _Q_PENDING_LOOPS;
+		val = atomic_cond_read_relaxed(&lock->val,
+					       (VAL != _Q_PENDING_VAL) || !cnt--);
+	}
+
+	/*
+	 * If we observe any contention; queue.
+	 */
+	if (val & ~_Q_LOCKED_MASK)
+		goto queue;
+
+	/*
+	 * trylock || pending
+	 *
+	 * 0,0,* -> 0,1,* -> 0,0,1 pending, trylock
+	 */
+	val = queued_fetch_set_pending_acquire(lock);
+
+	/*
+	 * If we observe contention, there is a concurrent locker.
+	 *
+	 * Undo and queue; our setting of PENDING might have made the
+	 * n,0,0 -> 0,0,0 transition fail and it will now be waiting
+	 * on @next to become !NULL.
+	 */
+	if (unlikely(val & ~_Q_LOCKED_MASK)) {
+
+		/* Undo PENDING if we set it. */
+		if (!(val & _Q_PENDING_MASK))
+			clear_pending(lock);
+
+		goto queue;
+	}
+
+	/*
+	 * We're pending, wait for the owner to go away.
+	 *
+	 * 0,1,1 -> *,1,0
+	 *
+	 * this wait loop must be a load-acquire such that we match the
+	 * store-release that clears the locked bit and create lock
+	 * sequentiality; this is because not all
+	 * clear_pending_set_locked() implementations imply full
+	 * barriers.
+	 */
+	if (val & _Q_LOCKED_MASK)
+		smp_cond_load_acquire(&lock->locked, !VAL);
+
+	/*
+	 * take ownership and clear the pending bit.
+	 *
+	 * 0,1,0 -> 0,0,1
+	 */
+	clear_pending_set_locked(lock);
+	lockevent_inc(lock_pending);
+	return;
+
+	/*
+	 * End of pending bit optimistic spinning and beginning of MCS
+	 * queuing.
+	 */
+queue:
+	lockevent_inc(lock_slowpath);
+pv_queue:
+	node = this_cpu_ptr(&rqnodes[0].mcs);
+	idx = node->count++;
+	tail = encode_tail(smp_processor_id(), idx);
+
+	trace_contention_begin(lock, LCB_F_SPIN);
+
+	/*
+	 * 4 nodes are allocated based on the assumption that there will
+	 * not be nested NMIs taking spinlocks. That may not be true in
+	 * some architectures even though the chance of needing more than
+	 * 4 nodes will still be extremely unlikely. When that happens,
+	 * we fall back to spinning on the lock directly without using
+	 * any MCS node. This is not the most elegant solution, but is
+	 * simple enough.
+	 */
+	if (unlikely(idx >= _Q_MAX_NODES)) {
+		lockevent_inc(lock_no_node);
+		while (!queued_spin_trylock(lock))
+			cpu_relax();
+		goto release;
+	}
+
+	node = grab_mcs_node(node, idx);
+
+	/*
+	 * Keep counts of non-zero index values:
+	 */
+	lockevent_cond_inc(lock_use_node2 + idx - 1, idx);
+
+	/*
+	 * Ensure that we increment the head node->count before initialising
+	 * the actual node. If the compiler is kind enough to reorder these
+	 * stores, then an IRQ could overwrite our assignments.
+	 */
+	barrier();
+
+	node->locked = 0;
+	node->next = NULL;
+	pv_init_node(node);
+
+	/*
+	 * We touched a (possibly) cold cacheline in the per-cpu queue node;
+	 * attempt the trylock once more in the hope someone let go while we
+	 * weren't watching.
+	 */
+	if (queued_spin_trylock(lock))
+		goto release;
+
+	/*
+	 * Ensure that the initialisation of @node is complete before we
+	 * publish the updated tail via xchg_tail() and potentially link
+	 * @node into the waitqueue via WRITE_ONCE(prev->next, node) below.
+	 */
+	smp_wmb();
+
+	/*
+	 * Publish the updated tail.
+	 * We have already touched the queueing cacheline; don't bother with
+	 * pending stuff.
+	 *
+	 * p,*,* -> n,*,*
+	 */
+	old = xchg_tail(lock, tail);
+	next = NULL;
+
+	/*
+	 * if there was a previous node; link it and wait until reaching the
+	 * head of the waitqueue.
+	 */
+	if (old & _Q_TAIL_MASK) {
+		prev = decode_tail(old, rqnodes);
+
+		/* Link @node into the waitqueue. */
+		WRITE_ONCE(prev->next, node);
+
+		pv_wait_node(node, prev);
+		arch_mcs_spin_lock_contended(&node->locked);
+
+		/*
+		 * While waiting for the MCS lock, the next pointer may have
+		 * been set by another lock waiter. We optimistically load
+		 * the next pointer & prefetch the cacheline for writing
+		 * to reduce latency in the upcoming MCS unlock operation.
+		 */
+		next = READ_ONCE(node->next);
+		if (next)
+			prefetchw(next);
+	}
+
+	/*
+	 * we're at the head of the waitqueue, wait for the owner & pending to
+	 * go away.
+	 *
+	 * *,x,y -> *,0,0
+	 *
+	 * this wait loop must use a load-acquire such that we match the
+	 * store-release that clears the locked bit and create lock
+	 * sequentiality; this is because the set_locked() function below
+	 * does not imply a full barrier.
+	 *
+	 * The PV pv_wait_head_or_lock function, if active, will acquire
+	 * the lock and return a non-zero value. So we have to skip the
+	 * atomic_cond_read_acquire() call. As the next PV queue head hasn't
+	 * been designated yet, there is no way for the locked value to become
+	 * _Q_SLOW_VAL. So both the set_locked() and the
+	 * atomic_cmpxchg_relaxed() calls will be safe.
+	 *
+	 * If PV isn't active, 0 will be returned instead.
+	 *
+	 */
+	if ((val = pv_wait_head_or_lock(lock, node)))
+		goto locked;
+
+	val = atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK));
+
+locked:
+	/*
+	 * claim the lock:
+	 *
+	 * n,0,0 -> 0,0,1 : lock, uncontended
+	 * *,*,0 -> *,*,1 : lock, contended
+	 *
+	 * If the queue head is the only one in the queue (lock value == tail)
+	 * and nobody is pending, clear the tail code and grab the lock.
+	 * Otherwise, we only need to grab the lock.
+	 */
+
+	/*
+	 * In the PV case we might already have _Q_LOCKED_VAL set, because
+	 * of lock stealing; therefore we must also allow:
+	 *
+	 * n,0,1 -> 0,0,1
+	 *
+	 * Note: at this point: (val & _Q_PENDING_MASK) == 0, because of the
+	 *       above wait condition, therefore any concurrent setting of
+	 *       PENDING will make the uncontended transition fail.
+	 */
+	if ((val & _Q_TAIL_MASK) == tail) {
+		if (atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL))
+			goto release; /* No contention */
+	}
+
+	/*
+	 * Either somebody is queued behind us or _Q_PENDING_VAL got set
+	 * which will then detect the remaining tail and queue behind us
+	 * ensuring we'll see a @next.
+	 */
+	set_locked(lock);
+
+	/*
+	 * contended path; wait for next if not observed yet, release.
+	 */
+	if (!next)
+		next = smp_cond_load_relaxed(&node->next, (VAL));
+
+	arch_mcs_spin_unlock_contended(&next->locked);
+	pv_kick_node(lock, next);
+
+release:
+	trace_contention_end(lock, 0);
+
+	/*
+	 * release the node
+	 */
+	__this_cpu_dec(rqnodes[0].mcs.count);
+}
+EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
+
+/*
+ * Generate the paravirt code for resilient_queued_spin_unlock_slowpath().
+ */
+#if !defined(_GEN_PV_LOCK_SLOWPATH) && defined(CONFIG_PARAVIRT_SPINLOCKS)
+#define _GEN_PV_LOCK_SLOWPATH
+
+#undef  pv_enabled
+#define pv_enabled()	true
+
+#undef pv_init_node
+#undef pv_wait_node
+#undef pv_kick_node
+#undef pv_wait_head_or_lock
+
+#undef  resilient_queued_spin_lock_slowpath
+#define resilient_queued_spin_lock_slowpath	__pv_resilient_queued_spin_lock_slowpath
+
+#include "../locking/qspinlock_paravirt.h"
+#include "rqspinlock.c"
+
+bool nopvspin;
+static __init int parse_nopvspin(char *arg)
+{
+	nopvspin = true;
+	return 0;
+}
+early_param("nopvspin", parse_nopvspin);
+#endif
-- 
2.47.1

[PATCH bpf-next v4 05/25] rqspinlock: Add rqspinlock.h header

[Kumar Kartikeya Dwivedi]

This header contains the public declarations usable in the rest of the
kernel for rqspinlock.

Let's also type alias qspinlock to rqspinlock_t to ensure consistent use
of the new lock type. We want to remove dependence on the qspinlock type
in later patches as we need to provide a test-and-set fallback, hence
begin abstracting away from now onwards.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/rqspinlock.h | 19 +++++++++++++++++++
 kernel/bpf/rqspinlock.c          |  3 ++-
 2 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 include/asm-generic/rqspinlock.h

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
new file mode 100644
index 000000000000..22f8094d0550
--- /dev/null
+++ b/include/asm-generic/rqspinlock.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Resilient Queued Spin Lock
+ *
+ * (C) Copyright 2024-2025 Meta Platforms, Inc. and affiliates.
+ *
+ * Authors: Kumar Kartikeya Dwivedi <memxor@gmail.com>
+ */
+#ifndef __ASM_GENERIC_RQSPINLOCK_H
+#define __ASM_GENERIC_RQSPINLOCK_H
+
+#include <linux/types.h>
+
+struct qspinlock;
+typedef struct qspinlock rqspinlock_t;
+
+extern void resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);
+
+#endif /* __ASM_GENERIC_RQSPINLOCK_H */
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 762108cb0f38..93e31633c2aa 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -23,6 +23,7 @@
 #include <asm/byteorder.h>
 #include <asm/qspinlock.h>
 #include <trace/events/lock.h>
+#include <asm/rqspinlock.h>
 
 /*
  * Include queued spinlock definitions and statistics code
@@ -127,7 +128,7 @@ static __always_inline u32  __pv_wait_head_or_lock(struct qspinlock *lock,
  * contended             :    (*,x,y) +--> (*,0,0) ---> (*,0,1) -'  :
  *   queue               :         ^--'                             :
  */
-void __lockfunc resilient_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
+void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 {
 	struct mcs_spinlock *prev, *next, *node;
 	u32 old, tail;
-- 
2.47.1

[PATCH bpf-next v4 06/25] rqspinlock: Drop PV and virtualization support

[Kumar Kartikeya Dwivedi]

Changes to rqspinlock in subsequent commits will be algorithmic
modifications, which won't remain in agreement with the implementations
of paravirt spin lock and virt_spin_lock support. These future changes
include measures for terminating waiting loops in slow path after a
certain point. While using a fair lock like qspinlock directly inside
virtual machines leads to suboptimal performance under certain
conditions, we cannot use the existing virtualization support before we
make it resilient as well.  Therefore, drop it for now.

Note that we need to drop qspinlock_stat.h, as it's only relevant in
case of CONFIG_PARAVIRT_SPINLOCKS=y, but we need to keep lock_events.h
in the includes, which was indirectly pulled in before.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/rqspinlock.c | 91 +----------------------------------------
 1 file changed, 1 insertion(+), 90 deletions(-)

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 93e31633c2aa..c2646cffc59e 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -11,8 +11,6 @@
  *          Peter Zijlstra <peterz@infradead.org>
  */
 
-#ifndef _GEN_PV_LOCK_SLOWPATH
-
 #include <linux/smp.h>
 #include <linux/bug.h>
 #include <linux/cpumask.h>
@@ -29,7 +27,7 @@
  * Include queued spinlock definitions and statistics code
  */
 #include "../locking/qspinlock.h"
-#include "../locking/qspinlock_stat.h"
+#include "../locking/lock_events.h"
 
 /*
  * The basic principle of a queue-based spinlock can best be understood
@@ -75,38 +73,9 @@
  * contexts: task, softirq, hardirq, nmi.
  *
  * Exactly fits one 64-byte cacheline on a 64-bit architecture.
- *
- * PV doubles the storage and uses the second cacheline for PV state.
  */
 static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
 
-/*
- * Generate the native code for resilient_queued_spin_unlock_slowpath(); provide NOPs
- * for all the PV callbacks.
- */
-
-static __always_inline void __pv_init_node(struct mcs_spinlock *node) { }
-static __always_inline void __pv_wait_node(struct mcs_spinlock *node,
-					   struct mcs_spinlock *prev) { }
-static __always_inline void __pv_kick_node(struct qspinlock *lock,
-					   struct mcs_spinlock *node) { }
-static __always_inline u32  __pv_wait_head_or_lock(struct qspinlock *lock,
-						   struct mcs_spinlock *node)
-						   { return 0; }
-
-#define pv_enabled()		false
-
-#define pv_init_node		__pv_init_node
-#define pv_wait_node		__pv_wait_node
-#define pv_kick_node		__pv_kick_node
-#define pv_wait_head_or_lock	__pv_wait_head_or_lock
-
-#ifdef CONFIG_PARAVIRT_SPINLOCKS
-#define resilient_queued_spin_lock_slowpath	native_resilient_queued_spin_lock_slowpath
-#endif
-
-#endif /* _GEN_PV_LOCK_SLOWPATH */
-
 /**
  * resilient_queued_spin_lock_slowpath - acquire the queued spinlock
  * @lock: Pointer to queued spinlock structure
@@ -136,12 +105,6 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 
 	BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));
 
-	if (pv_enabled())
-		goto pv_queue;
-
-	if (virt_spin_lock(lock))
-		return;
-
 	/*
 	 * Wait for in-progress pending->locked hand-overs with a bounded
 	 * number of spins so that we guarantee forward progress.
@@ -212,7 +175,6 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 queue:
 	lockevent_inc(lock_slowpath);
-pv_queue:
 	node = this_cpu_ptr(&rqnodes[0].mcs);
 	idx = node->count++;
 	tail = encode_tail(smp_processor_id(), idx);
@@ -251,7 +213,6 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 
 	node->locked = 0;
 	node->next = NULL;
-	pv_init_node(node);
 
 	/*
 	 * We touched a (possibly) cold cacheline in the per-cpu queue node;
@@ -288,7 +249,6 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 		/* Link @node into the waitqueue. */
 		WRITE_ONCE(prev->next, node);
 
-		pv_wait_node(node, prev);
 		arch_mcs_spin_lock_contended(&node->locked);
 
 		/*
@@ -312,23 +272,9 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 * store-release that clears the locked bit and create lock
 	 * sequentiality; this is because the set_locked() function below
 	 * does not imply a full barrier.
-	 *
-	 * The PV pv_wait_head_or_lock function, if active, will acquire
-	 * the lock and return a non-zero value. So we have to skip the
-	 * atomic_cond_read_acquire() call. As the next PV queue head hasn't
-	 * been designated yet, there is no way for the locked value to become
-	 * _Q_SLOW_VAL. So both the set_locked() and the
-	 * atomic_cmpxchg_relaxed() calls will be safe.
-	 *
-	 * If PV isn't active, 0 will be returned instead.
-	 *
 	 */
-	if ((val = pv_wait_head_or_lock(lock, node)))
-		goto locked;
-
 	val = atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK));
 
-locked:
 	/*
 	 * claim the lock:
 	 *
@@ -341,11 +287,6 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 
 	/*
-	 * In the PV case we might already have _Q_LOCKED_VAL set, because
-	 * of lock stealing; therefore we must also allow:
-	 *
-	 * n,0,1 -> 0,0,1
-	 *
 	 * Note: at this point: (val & _Q_PENDING_MASK) == 0, because of the
 	 *       above wait condition, therefore any concurrent setting of
 	 *       PENDING will make the uncontended transition fail.
@@ -369,7 +310,6 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 		next = smp_cond_load_relaxed(&node->next, (VAL));
 
 	arch_mcs_spin_unlock_contended(&next->locked);
-	pv_kick_node(lock, next);
 
 release:
 	trace_contention_end(lock, 0);
@@ -380,32 +320,3 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	__this_cpu_dec(rqnodes[0].mcs.count);
 }
 EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
-
-/*
- * Generate the paravirt code for resilient_queued_spin_unlock_slowpath().
- */
-#if !defined(_GEN_PV_LOCK_SLOWPATH) && defined(CONFIG_PARAVIRT_SPINLOCKS)
-#define _GEN_PV_LOCK_SLOWPATH
-
-#undef  pv_enabled
-#define pv_enabled()	true
-
-#undef pv_init_node
-#undef pv_wait_node
-#undef pv_kick_node
-#undef pv_wait_head_or_lock
-
-#undef  resilient_queued_spin_lock_slowpath
-#define resilient_queued_spin_lock_slowpath	__pv_resilient_queued_spin_lock_slowpath
-
-#include "../locking/qspinlock_paravirt.h"
-#include "rqspinlock.c"
-
-bool nopvspin;
-static __init int parse_nopvspin(char *arg)
-{
-	nopvspin = true;
-	return 0;
-}
-early_param("nopvspin", parse_nopvspin);
-#endif
-- 
2.47.1

[PATCH bpf-next v4 07/25] rqspinlock: Add support for timeouts

[Kumar Kartikeya Dwivedi]

Introduce policy macro RES_CHECK_TIMEOUT which can be used to detect
when the timeout has expired for the slow path to return an error. It
depends on being passed two variables initialized to 0: ts, ret. The
'ts' parameter is of type rqspinlock_timeout.

This macro resolves to the (ret) expression so that it can be used in
statements like smp_cond_load_acquire to break the waiting loop
condition.

The 'spin' member is used to amortize the cost of checking time by
dispatching to the implementation every 64k iterations. The
'timeout_end' member is used to keep track of the timestamp that denotes
the end of the waiting period. The 'ret' parameter denotes the status of
the timeout, and can be checked in the slow path to detect timeouts
after waiting loops.

The 'duration' member is used to store the timeout duration for each
waiting loop. The default timeout value defined in the header
(RES_DEF_TIMEOUT) is 0.25 seconds.

This macro will be used as a condition for waiting loops in the slow
path.  Since each waiting loop applies a fresh timeout using the same
rqspinlock_timeout, we add a new RES_RESET_TIMEOUT as well to ensure the
values can be easily reinitialized to the default state.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/rqspinlock.h |  6 +++++
 kernel/bpf/rqspinlock.c          | 45 ++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 22f8094d0550..5dd4dd8aee69 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -10,10 +10,16 @@
 #define __ASM_GENERIC_RQSPINLOCK_H
 
 #include <linux/types.h>
+#include <vdso/time64.h>
 
 struct qspinlock;
 typedef struct qspinlock rqspinlock_t;
 
 extern void resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);
 
+/*
+ * Default timeout for waiting loops is 0.25 seconds
+ */
+#define RES_DEF_TIMEOUT (NSEC_PER_SEC / 4)
+
 #endif /* __ASM_GENERIC_RQSPINLOCK_H */
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index c2646cffc59e..0d8964b4d44a 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -6,9 +6,11 @@
  * (C) Copyright 2013-2014,2018 Red Hat, Inc.
  * (C) Copyright 2015 Intel Corp.
  * (C) Copyright 2015 Hewlett-Packard Enterprise Development LP
+ * (C) Copyright 2024-2025 Meta Platforms, Inc. and affiliates.
  *
  * Authors: Waiman Long <longman@redhat.com>
  *          Peter Zijlstra <peterz@infradead.org>
+ *          Kumar Kartikeya Dwivedi <memxor@gmail.com>
  */
 
 #include <linux/smp.h>
@@ -22,6 +24,7 @@
 #include <asm/qspinlock.h>
 #include <trace/events/lock.h>
 #include <asm/rqspinlock.h>
+#include <linux/timekeeping.h>
 
 /*
  * Include queued spinlock definitions and statistics code
@@ -68,6 +71,45 @@
 
 #include "../locking/mcs_spinlock.h"
 
+struct rqspinlock_timeout {
+	u64 timeout_end;
+	u64 duration;
+	u16 spin;
+};
+
+static noinline int check_timeout(struct rqspinlock_timeout *ts)
+{
+	u64 time = ktime_get_mono_fast_ns();
+
+	if (!ts->timeout_end) {
+		ts->timeout_end = time + ts->duration;
+		return 0;
+	}
+
+	if (time > ts->timeout_end)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+#define RES_CHECK_TIMEOUT(ts, ret)                    \
+	({                                            \
+		if (!(ts).spin++)                     \
+			(ret) = check_timeout(&(ts)); \
+		(ret);                                \
+	})
+
+/*
+ * Initialize the 'spin' member.
+ */
+#define RES_INIT_TIMEOUT(ts) ({ (ts).spin = 1; })
+
+/*
+ * We only need to reset 'timeout_end', 'spin' will just wrap around as necessary.
+ * Duration is defined for each spin attempt, so set it here.
+ */
+#define RES_RESET_TIMEOUT(ts, _duration) ({ (ts).timeout_end = 0; (ts).duration = _duration; })
+
 /*
  * Per-CPU queue node structures; we can never have more than 4 nested
  * contexts: task, softirq, hardirq, nmi.
@@ -100,11 +142,14 @@ static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
 void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 {
 	struct mcs_spinlock *prev, *next, *node;
+	struct rqspinlock_timeout ts;
 	u32 old, tail;
 	int idx;
 
 	BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));
 
+	RES_INIT_TIMEOUT(ts);
+
 	/*
 	 * Wait for in-progress pending->locked hand-overs with a bounded
 	 * number of spins so that we guarantee forward progress.
-- 
2.47.1

[PATCH bpf-next v4 08/25] rqspinlock: Hardcode cond_acquire loops for arm64

[Kumar Kartikeya Dwivedi]

Currently, for rqspinlock usage, the implementation of
smp_cond_load_acquire (and thus, atomic_cond_read_acquire) are
susceptible to stalls on arm64, because they do not guarantee that the
conditional expression will be repeatedly invoked if the address being
loaded from is not written to by other CPUs. When support for
event-streams is absent (which unblocks stuck WFE-based loops every
~100us), we may end up being stuck forever.

This causes a problem for us, as we need to repeatedly invoke the
RES_CHECK_TIMEOUT in the spin loop to break out when the timeout
expires.

Let us import the smp_cond_load_acquire_timewait implementation Ankur is
proposing in [0], and then fallback to it once it is merged.

While we rely on the implementation to amortize the cost of sampling
check_timeout for us, it will not happen when event stream support is
unavailable. This is not the common case, and it would be difficult to
fit our logic in the time_expr_ns >= time_limit_ns comparison, hence
just let it be.

  [0]: https://lore.kernel.org/lkml/20250203214911.898276-1-ankur.a.arora@oracle.com

Cc: Ankur Arora <ankur.a.arora@oracle.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 arch/arm64/include/asm/rqspinlock.h | 93 +++++++++++++++++++++++++++++
 kernel/bpf/rqspinlock.c             | 15 +++++
 2 files changed, 108 insertions(+)
 create mode 100644 arch/arm64/include/asm/rqspinlock.h

diff --git a/arch/arm64/include/asm/rqspinlock.h b/arch/arm64/include/asm/rqspinlock.h
new file mode 100644
index 000000000000..5b80785324b6
--- /dev/null
+++ b/arch/arm64/include/asm/rqspinlock.h
@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RQSPINLOCK_H
+#define _ASM_RQSPINLOCK_H
+
+#include <asm/barrier.h>
+
+/*
+ * Hardcode res_smp_cond_load_acquire implementations for arm64 to a custom
+ * version based on [0]. In rqspinlock code, our conditional expression involves
+ * checking the value _and_ additionally a timeout. However, on arm64, the
+ * WFE-based implementation may never spin again if no stores occur to the
+ * locked byte in the lock word. As such, we may be stuck forever if
+ * event-stream based unblocking is not available on the platform for WFE spin
+ * loops (arch_timer_evtstrm_available).
+ *
+ * Once support for smp_cond_load_acquire_timewait [0] lands, we can drop this
+ * copy-paste.
+ *
+ * While we rely on the implementation to amortize the cost of sampling
+ * cond_expr for us, it will not happen when event stream support is
+ * unavailable, time_expr check is amortized. This is not the common case, and
+ * it would be difficult to fit our logic in the time_expr_ns >= time_limit_ns
+ * comparison, hence just let it be. In case of event-stream, the loop is woken
+ * up at microsecond granularity.
+ *
+ * [0]: https://lore.kernel.org/lkml/20250203214911.898276-1-ankur.a.arora@oracle.com
+ */
+
+#ifndef smp_cond_load_acquire_timewait
+
+#define smp_cond_time_check_count	200
+
+#define __smp_cond_load_relaxed_spinwait(ptr, cond_expr, time_expr_ns,	\
+					 time_limit_ns) ({		\
+	typeof(ptr) __PTR = (ptr);					\
+	__unqual_scalar_typeof(*ptr) VAL;				\
+	unsigned int __count = 0;					\
+	for (;;) {							\
+		VAL = READ_ONCE(*__PTR);				\
+		if (cond_expr)						\
+			break;						\
+		cpu_relax();						\
+		if (__count++ < smp_cond_time_check_count)		\
+			continue;					\
+		if ((time_expr_ns) >= (time_limit_ns))			\
+			break;						\
+		__count = 0;						\
+	}								\
+	(typeof(*ptr))VAL;						\
+})
+
+#define __smp_cond_load_acquire_timewait(ptr, cond_expr,		\
+					 time_expr_ns, time_limit_ns)	\
+({									\
+	typeof(ptr) __PTR = (ptr);					\
+	__unqual_scalar_typeof(*ptr) VAL;				\
+	for (;;) {							\
+		VAL = smp_load_acquire(__PTR);				\
+		if (cond_expr)						\
+			break;						\
+		__cmpwait_relaxed(__PTR, VAL);				\
+		if ((time_expr_ns) >= (time_limit_ns))			\
+			break;						\
+	}								\
+	(typeof(*ptr))VAL;						\
+})
+
+#define smp_cond_load_acquire_timewait(ptr, cond_expr,			\
+				      time_expr_ns, time_limit_ns)	\
+({									\
+	__unqual_scalar_typeof(*ptr) _val;				\
+	int __wfe = arch_timer_evtstrm_available();			\
+									\
+	if (likely(__wfe)) {						\
+		_val = __smp_cond_load_acquire_timewait(ptr, cond_expr,	\
+							time_expr_ns,	\
+							time_limit_ns);	\
+	} else {							\
+		_val = __smp_cond_load_relaxed_spinwait(ptr, cond_expr,	\
+							time_expr_ns,	\
+							time_limit_ns);	\
+		smp_acquire__after_ctrl_dep();				\
+	}								\
+	(typeof(*ptr))_val;						\
+})
+
+#endif
+
+#define res_smp_cond_load_acquire_timewait(v, c) smp_cond_load_acquire_timewait(v, c, 0, 1)
+
+#include <asm-generic/rqspinlock.h>
+
+#endif /* _ASM_RQSPINLOCK_H */
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 0d8964b4d44a..d429b923b58f 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -92,12 +92,21 @@ static noinline int check_timeout(struct rqspinlock_timeout *ts)
 	return 0;
 }
 
+/*
+ * Do not amortize with spins when res_smp_cond_load_acquire is defined,
+ * as the macro does internal amortization for us.
+ */
+#ifndef res_smp_cond_load_acquire
 #define RES_CHECK_TIMEOUT(ts, ret)                    \
 	({                                            \
 		if (!(ts).spin++)                     \
 			(ret) = check_timeout(&(ts)); \
 		(ret);                                \
 	})
+#else
+#define RES_CHECK_TIMEOUT(ts, ret, mask)	      \
+	({ (ret) = check_timeout(&(ts)); })
+#endif
 
 /*
  * Initialize the 'spin' member.
@@ -118,6 +127,12 @@ static noinline int check_timeout(struct rqspinlock_timeout *ts)
  */
 static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
 
+#ifndef res_smp_cond_load_acquire
+#define res_smp_cond_load_acquire(v, c) smp_cond_load_acquire(v, c)
+#endif
+
+#define res_atomic_cond_read_acquire(v, c) res_smp_cond_load_acquire(&(v)->counter, (c))
+
 /**
  * resilient_queued_spin_lock_slowpath - acquire the queued spinlock
  * @lock: Pointer to queued spinlock structure
-- 
2.47.1

[PATCH bpf-next v4 09/25] rqspinlock: Protect pending bit owners from stalls

[Kumar Kartikeya Dwivedi]

The pending bit is used to avoid queueing in case the lock is
uncontended, and has demonstrated benefits for the 2 contender scenario,
esp. on x86. In case the pending bit is acquired and we wait for the
locked bit to disappear, we may get stuck due to the lock owner not
making progress. Hence, this waiting loop must be protected with a
timeout check.

To perform a graceful recovery once we decide to abort our lock
acquisition attempt in this case, we must unset the pending bit since we
own it. All waiters undoing their changes and exiting gracefully allows
the lock word to be restored to the unlocked state once all participants
(owner, waiters) have been recovered, and the lock remains usable.
Hence, set the pending bit back to zero before returning to the caller.

Introduce a lockevent (rqspinlock_lock_timeout) to capture timeout
event statistics.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/rqspinlock.h  |  2 +-
 kernel/bpf/rqspinlock.c           | 32 ++++++++++++++++++++++++++-----
 kernel/locking/lock_events_list.h |  5 +++++
 3 files changed, 33 insertions(+), 6 deletions(-)

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 5dd4dd8aee69..9bd11cb7acd6 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -15,7 +15,7 @@
 struct qspinlock;
 typedef struct qspinlock rqspinlock_t;
 
-extern void resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);
+extern int resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);
 
 /*
  * Default timeout for waiting loops is 0.25 seconds
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index d429b923b58f..262294cfd36f 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -138,6 +138,10 @@ static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
  * @lock: Pointer to queued spinlock structure
  * @val: Current value of the queued spinlock 32-bit word
  *
+ * Return:
+ * * 0		- Lock was acquired successfully.
+ * * -ETIMEDOUT - Lock acquisition failed because of timeout.
+ *
  * (queue tail, pending bit, lock value)
  *
  *              fast     :    slow                                  :    unlock
@@ -154,12 +158,12 @@ static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
  * contended             :    (*,x,y) +--> (*,0,0) ---> (*,0,1) -'  :
  *   queue               :         ^--'                             :
  */
-void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
+int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 {
 	struct mcs_spinlock *prev, *next, *node;
 	struct rqspinlock_timeout ts;
+	int idx, ret = 0;
 	u32 old, tail;
-	int idx;
 
 	BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));
 
@@ -217,8 +221,25 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 * clear_pending_set_locked() implementations imply full
 	 * barriers.
 	 */
-	if (val & _Q_LOCKED_MASK)
-		smp_cond_load_acquire(&lock->locked, !VAL);
+	if (val & _Q_LOCKED_MASK) {
+		RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT);
+		res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret));
+	}
+
+	if (ret) {
+		/*
+		 * We waited for the locked bit to go back to 0, as the pending
+		 * waiter, but timed out. We need to clear the pending bit since
+		 * we own it. Once a stuck owner has been recovered, the lock
+		 * must be restored to a valid state, hence removing the pending
+		 * bit is necessary.
+		 *
+		 * *,1,* -> *,0,*
+		 */
+		clear_pending(lock);
+		lockevent_inc(rqspinlock_lock_timeout);
+		return ret;
+	}
 
 	/*
 	 * take ownership and clear the pending bit.
@@ -227,7 +248,7 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 	clear_pending_set_locked(lock);
 	lockevent_inc(lock_pending);
-	return;
+	return 0;
 
 	/*
 	 * End of pending bit optimistic spinning and beginning of MCS
@@ -378,5 +399,6 @@ void __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 * release the node
 	 */
 	__this_cpu_dec(rqnodes[0].mcs.count);
+	return 0;
 }
 EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
diff --git a/kernel/locking/lock_events_list.h b/kernel/locking/lock_events_list.h
index 97fb6f3f840a..c5286249994d 100644
--- a/kernel/locking/lock_events_list.h
+++ b/kernel/locking/lock_events_list.h
@@ -49,6 +49,11 @@ LOCK_EVENT(lock_use_node4)	/* # of locking ops that use 4th percpu node */
 LOCK_EVENT(lock_no_node)	/* # of locking ops w/o using percpu node    */
 #endif /* CONFIG_QUEUED_SPINLOCKS */
 
+/*
+ * Locking events for Resilient Queued Spin Lock
+ */
+LOCK_EVENT(rqspinlock_lock_timeout)	/* # of locking ops that timeout	*/
+
 /*
  * Locking events for rwsem
  */
-- 
2.47.1

[PATCH bpf-next v4 10/25] rqspinlock: Protect waiters in queue from stalls

[Kumar Kartikeya Dwivedi]

Implement the wait queue cleanup algorithm for rqspinlock. There are
three forms of waiters in the original queued spin lock algorithm. The
first is the waiter which acquires the pending bit and spins on the lock
word without forming a wait queue. The second is the head waiter that is
the first waiter heading the wait queue. The third form is of all the
non-head waiters queued behind the head, waiting to be signalled through
their MCS node to overtake the responsibility of the head.

In this commit, we are concerned with the second and third kind. First,
we augment the waiting loop of the head of the wait queue with a
timeout. When this timeout happens, all waiters part of the wait queue
will abort their lock acquisition attempts. This happens in three steps.
First, the head breaks out of its loop waiting for pending and locked
bits to turn to 0, and non-head waiters break out of their MCS node spin
(more on that later). Next, every waiter (head or non-head) attempts to
check whether they are also the tail waiter, in such a case they attempt
to zero out the tail word and allow a new queue to be built up for this
lock. If they succeed, they have no one to signal next in the queue to
stop spinning. Otherwise, they signal the MCS node of the next waiter to
break out of its spin and try resetting the tail word back to 0. This
goes on until the tail waiter is found. In case of races, the new tail
will be responsible for performing the same task, as the old tail will
then fail to reset the tail word and wait for its next pointer to be
updated before it signals the new tail to do the same.

We terminate the whole wait queue because of two main reasons. Firstly,
we eschew per-waiter timeouts with one applied at the head of the wait
queue.  This allows everyone to break out faster once we've seen the
owner / pending waiter not responding for the timeout duration from the
head.  Secondly, it avoids complicated synchronization, because when not
leaving in FIFO order, prev's next pointer needs to be fixed up etc.

Lastly, all of these waiters release the rqnode and return to the
caller. This patch underscores the point that rqspinlock's timeout does
not apply to each waiter individually, and cannot be relied upon as an
upper bound. It is possible for the rqspinlock waiters to return early
from a failed lock acquisition attempt as soon as stalls are detected.

The head waiter cannot directly WRITE_ONCE the tail to zero, as it may
race with a concurrent xchg and a non-head waiter linking its MCS node
to the head's MCS node through 'prev->next' assignment.

One notable thing is that we must use RES_DEF_TIMEOUT * 2 as our maximum
duration for the waiting loop (for the wait queue head), since we may
have both the owner and pending bit waiter ahead of us, and in the worst
case, need to span their maximum permitted critical section lengths.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/rqspinlock.c | 55 ++++++++++++++++++++++++++++++++++++++---
 kernel/bpf/rqspinlock.h | 48 +++++++++++++++++++++++++++++++++++
 2 files changed, 100 insertions(+), 3 deletions(-)
 create mode 100644 kernel/bpf/rqspinlock.h

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 262294cfd36f..65c2b41d8937 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -77,6 +77,8 @@ struct rqspinlock_timeout {
 	u16 spin;
 };
 
+#define RES_TIMEOUT_VAL	2
+
 static noinline int check_timeout(struct rqspinlock_timeout *ts)
 {
 	u64 time = ktime_get_mono_fast_ns();
@@ -325,12 +327,18 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 * head of the waitqueue.
 	 */
 	if (old & _Q_TAIL_MASK) {
+		int val;
+
 		prev = decode_tail(old, rqnodes);
 
 		/* Link @node into the waitqueue. */
 		WRITE_ONCE(prev->next, node);
 
-		arch_mcs_spin_lock_contended(&node->locked);
+		val = arch_mcs_spin_lock_contended(&node->locked);
+		if (val == RES_TIMEOUT_VAL) {
+			ret = -EDEADLK;
+			goto waitq_timeout;
+		}
 
 		/*
 		 * While waiting for the MCS lock, the next pointer may have
@@ -353,8 +361,49 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 * store-release that clears the locked bit and create lock
 	 * sequentiality; this is because the set_locked() function below
 	 * does not imply a full barrier.
+	 *
+	 * We use RES_DEF_TIMEOUT * 2 as the duration, as RES_DEF_TIMEOUT is
+	 * meant to span maximum allowed time per critical section, and we may
+	 * have both the owner of the lock and the pending bit waiter ahead of
+	 * us.
 	 */
-	val = atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK));
+	RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT * 2);
+	val = res_atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK) ||
+					   RES_CHECK_TIMEOUT(ts, ret));
+
+waitq_timeout:
+	if (ret) {
+		/*
+		 * If the tail is still pointing to us, then we are the final waiter,
+		 * and are responsible for resetting the tail back to 0. Otherwise, if
+		 * the cmpxchg operation fails, we signal the next waiter to take exit
+		 * and try the same. For a waiter with tail node 'n':
+		 *
+		 * n,*,* -> 0,*,*
+		 *
+		 * When performing cmpxchg for the whole word (NR_CPUS > 16k), it is
+		 * possible locked/pending bits keep changing and we see failures even
+		 * when we remain the head of wait queue. However, eventually,
+		 * pending bit owner will unset the pending bit, and new waiters
+		 * will queue behind us. This will leave the lock owner in
+		 * charge, and it will eventually either set locked bit to 0, or
+		 * leave it as 1, allowing us to make progress.
+		 *
+		 * We terminate the whole wait queue for two reasons. Firstly,
+		 * we eschew per-waiter timeouts with one applied at the head of
+		 * the wait queue.  This allows everyone to break out faster
+		 * once we've seen the owner / pending waiter not responding for
+		 * the timeout duration from the head.  Secondly, it avoids
+		 * complicated synchronization, because when not leaving in FIFO
+		 * order, prev's next pointer needs to be fixed up etc.
+		 */
+		if (!try_cmpxchg_tail(lock, tail, 0)) {
+			next = smp_cond_load_relaxed(&node->next, VAL);
+			WRITE_ONCE(next->locked, RES_TIMEOUT_VAL);
+		}
+		lockevent_inc(rqspinlock_lock_timeout);
+		goto release;
+	}
 
 	/*
 	 * claim the lock:
@@ -399,6 +448,6 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 * release the node
 	 */
 	__this_cpu_dec(rqnodes[0].mcs.count);
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
diff --git a/kernel/bpf/rqspinlock.h b/kernel/bpf/rqspinlock.h
new file mode 100644
index 000000000000..5d8cb1b1aab4
--- /dev/null
+++ b/kernel/bpf/rqspinlock.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Resilient Queued Spin Lock defines
+ *
+ * (C) Copyright 2024-2025 Meta Platforms, Inc. and affiliates.
+ *
+ * Authors: Kumar Kartikeya Dwivedi <memxor@gmail.com>
+ */
+#ifndef __LINUX_RQSPINLOCK_H
+#define __LINUX_RQSPINLOCK_H
+
+#include "../locking/qspinlock.h"
+
+/*
+ * try_cmpxchg_tail - Return result of cmpxchg of tail word with a new value
+ * @lock: Pointer to queued spinlock structure
+ * @tail: The tail to compare against
+ * @new_tail: The new queue tail code word
+ * Return: Bool to indicate whether the cmpxchg operation succeeded
+ *
+ * This is used by the head of the wait queue to clean up the queue.
+ * Provides relaxed ordering, since observers only rely on initialized
+ * state of the node which was made visible through the xchg_tail operation,
+ * i.e. through the smp_wmb preceding xchg_tail.
+ *
+ * We avoid using 16-bit cmpxchg, which is not available on all architectures.
+ */
+static __always_inline bool try_cmpxchg_tail(struct qspinlock *lock, u32 tail, u32 new_tail)
+{
+	u32 old, new;
+
+	old = atomic_read(&lock->val);
+	do {
+		/*
+		 * Is the tail part we compare to already stale? Fail.
+		 */
+		if ((old & _Q_TAIL_MASK) != tail)
+			return false;
+		/*
+		 * Encode latest locked/pending state for new tail.
+		 */
+		new = (old & _Q_LOCKED_PENDING_MASK) | new_tail;
+	} while (!atomic_try_cmpxchg_relaxed(&lock->val, &old, new));
+
+	return true;
+}
+
+#endif /* __LINUX_RQSPINLOCK_H */
-- 
2.47.1

[PATCH bpf-next v4 11/25] rqspinlock: Protect waiters in trylock fallback from stalls

[Kumar Kartikeya Dwivedi]

When we run out of maximum rqnodes, the original queued spin lock slow
path falls back to a try lock. In such a case, we are again susceptible
to stalls in case the lock owner fails to make progress. We use the
timeout as a fallback to break out of this loop and return to the
caller. This is a fallback for an extreme edge case, when on the same
CPU we run out of all 4 qnodes. When could this happen? We are in slow
path in task context, we get interrupted by an IRQ, which while in the
slow path gets interrupted by an NMI, whcih in the slow path gets
another nested NMI, which enters the slow path. All of the interruptions
happen after node->count++.

We use RES_DEF_TIMEOUT as our spinning duration, but in the case of this
fallback, no fairness is guaranteed, so the duration may be too small
for contended cases, as the waiting time is not bounded. Since this is
an extreme corner case, let's just prefer timing out instead of
attempting to spin for longer.

Reviewed-by: Barret Rhoden <brho@google.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/rqspinlock.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 65c2b41d8937..361d452f027c 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -275,8 +275,14 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 	if (unlikely(idx >= _Q_MAX_NODES)) {
 		lockevent_inc(lock_no_node);
-		while (!queued_spin_trylock(lock))
+		RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT);
+		while (!queued_spin_trylock(lock)) {
+			if (RES_CHECK_TIMEOUT(ts, ret)) {
+				lockevent_inc(rqspinlock_lock_timeout);
+				break;
+			}
 			cpu_relax();
+		}
 		goto release;
 	}
 
-- 
2.47.1

[PATCH bpf-next v4 12/25] rqspinlock: Add deadlock detection and recovery

[Kumar Kartikeya Dwivedi]

While the timeout logic provides guarantees for the waiter's forward
progress, the time until a stalling waiter unblocks can still be long.
The default timeout of 1/4 sec can be excessively long for some use
cases.  Additionally, custom timeouts may exacerbate recovery time.

Introduce logic to detect common cases of deadlocks and perform quicker
recovery. This is done by dividing the time from entry into the locking
slow path until the timeout into intervals of 1 ms. Then, after each
interval elapses, deadlock detection is performed, while also polling
the lock word to ensure we can quickly break out of the detection logic
and proceed with lock acquisition.

A 'held_locks' table is maintained per-CPU where the entry at the bottom
denotes a lock being waited for or already taken. Entries coming before
it denote locks that are already held. The current CPU's table can thus
be looked at to detect AA deadlocks. The tables from other CPUs can be
looked at to discover ABBA situations. Finally, when a matching entry
for the lock being taken on the current CPU is found on some other CPU,
a deadlock situation is detected. This function can take a long time,
therefore the lock word is constantly polled in each loop iteration to
ensure we can preempt detection and proceed with lock acquisition, using
the is_lock_released check.

We set 'spin' member of rqspinlock_timeout struct to 0 to trigger
deadlock checks immediately to perform faster recovery.

Note: Extending lock word size by 4 bytes to record owner CPU can allow
faster detection for ABBA. It is typically the owner which participates
in a ABBA situation. However, to keep compatibility with existing lock
words in the kernel (struct qspinlock), and given deadlocks are a rare
event triggered by bugs, we choose to favor compatibility over faster
detection.

The release_held_lock_entry function requires an smp_wmb, while the
release store on unlock will provide the necessary ordering for us. Add
comments to document the subtleties of why this is correct. It is
possible for stores to be reordered still, but in the context of the
deadlock detection algorithm, a release barrier is sufficient and
needn't be stronger for unlock's case.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/rqspinlock.h | 100 +++++++++++++++++
 kernel/bpf/rqspinlock.c          | 187 ++++++++++++++++++++++++++++---
 2 files changed, 273 insertions(+), 14 deletions(-)

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 9bd11cb7acd6..34c3dcb4299e 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -11,6 +11,7 @@
 
 #include <linux/types.h>
 #include <vdso/time64.h>
+#include <linux/percpu.h>
 
 struct qspinlock;
 typedef struct qspinlock rqspinlock_t;
@@ -22,4 +23,103 @@ extern int resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);
  */
 #define RES_DEF_TIMEOUT (NSEC_PER_SEC / 4)
 
+/*
+ * Choose 31 as it makes rqspinlock_held cacheline-aligned.
+ */
+#define RES_NR_HELD 31
+
+struct rqspinlock_held {
+	int cnt;
+	void *locks[RES_NR_HELD];
+};
+
+DECLARE_PER_CPU_ALIGNED(struct rqspinlock_held, rqspinlock_held_locks);
+
+static __always_inline void grab_held_lock_entry(void *lock)
+{
+	int cnt = this_cpu_inc_return(rqspinlock_held_locks.cnt);
+
+	if (unlikely(cnt > RES_NR_HELD)) {
+		/* Still keep the inc so we decrement later. */
+		return;
+	}
+
+	/*
+	 * Implied compiler barrier in per-CPU operations; otherwise we can have
+	 * the compiler reorder inc with write to table, allowing interrupts to
+	 * overwrite and erase our write to the table (as on interrupt exit it
+	 * will be reset to NULL).
+	 *
+	 * It is fine for cnt inc to be reordered wrt remote readers though,
+	 * they won't observe our entry until the cnt update is visible, that's
+	 * all.
+	 */
+	this_cpu_write(rqspinlock_held_locks.locks[cnt - 1], lock);
+}
+
+/*
+ * We simply don't support out-of-order unlocks, and keep the logic simple here.
+ * The verifier prevents BPF programs from unlocking out-of-order, and the same
+ * holds for in-kernel users.
+ *
+ * It is possible to run into misdetection scenarios of AA deadlocks on the same
+ * CPU, and missed ABBA deadlocks on remote CPUs if this function pops entries
+ * out of order (due to lock A, lock B, unlock A, unlock B) pattern. The correct
+ * logic to preserve right entries in the table would be to walk the array of
+ * held locks and swap and clear out-of-order entries, but that's too
+ * complicated and we don't have a compelling use case for out of order unlocking.
+ */
+static __always_inline void release_held_lock_entry(void)
+{
+	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
+
+	if (unlikely(rqh->cnt > RES_NR_HELD))
+		goto dec;
+	WRITE_ONCE(rqh->locks[rqh->cnt - 1], NULL);
+dec:
+	/*
+	 * Reordering of clearing above with inc and its write in
+	 * grab_held_lock_entry that came before us (in same acquisition
+	 * attempt) is ok, we either see a valid entry or NULL when it's
+	 * visible.
+	 *
+	 * But this helper is invoked when we unwind upon failing to acquire the
+	 * lock. Unlike the unlock path which constitutes a release store after
+	 * we clear the entry, we need to emit a write barrier here. Otherwise,
+	 * we may have a situation as follows:
+	 *
+	 * <error> for lock B
+	 * release_held_lock_entry
+	 *
+	 * try_cmpxchg_acquire for lock A
+	 * grab_held_lock_entry
+	 *
+	 * Lack of any ordering means reordering may occur such that dec, inc
+	 * are done before entry is overwritten. This permits a remote lock
+	 * holder of lock B (which this CPU failed to acquire) to now observe it
+	 * as being attempted on this CPU, and may lead to misdetection (if this
+	 * CPU holds a lock it is attempting to acquire, leading to false ABBA
+	 * diagnosis).
+	 *
+	 * In case of unlock, we will always do a release on the lock word after
+	 * releasing the entry, ensuring that other CPUs cannot hold the lock
+	 * (and make conclusions about deadlocks) until the entry has been
+	 * cleared on the local CPU, preventing any anomalies. Reordering is
+	 * still possible there, but a remote CPU cannot observe a lock in our
+	 * table which it is already holding, since visibility entails our
+	 * release store for the said lock has not retired.
+	 *
+	 * In theory we don't have a problem if the dec and WRITE_ONCE above get
+	 * reordered with each other, we either notice an empty NULL entry on
+	 * top (if dec succeeds WRITE_ONCE), or a potentially stale entry which
+	 * cannot be observed (if dec precedes WRITE_ONCE).
+	 *
+	 * Emit the write barrier _before_ the dec, this permits dec-inc
+	 * reordering but that is harmless as we'd have new entry set to NULL
+	 * already, i.e. they cannot precede the NULL store above.
+	 */
+	smp_wmb();
+	this_cpu_dec(rqspinlock_held_locks.cnt);
+}
+
 #endif /* __ASM_GENERIC_RQSPINLOCK_H */
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 361d452f027c..bddbcc47d38f 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -31,6 +31,7 @@
  */
 #include "../locking/qspinlock.h"
 #include "../locking/lock_events.h"
+#include "rqspinlock.h"
 
 /*
  * The basic principle of a queue-based spinlock can best be understood
@@ -74,16 +75,147 @@
 struct rqspinlock_timeout {
 	u64 timeout_end;
 	u64 duration;
+	u64 cur;
 	u16 spin;
 };
 
 #define RES_TIMEOUT_VAL	2
 
-static noinline int check_timeout(struct rqspinlock_timeout *ts)
+DEFINE_PER_CPU_ALIGNED(struct rqspinlock_held, rqspinlock_held_locks);
+EXPORT_SYMBOL_GPL(rqspinlock_held_locks);
+
+static bool is_lock_released(rqspinlock_t *lock, u32 mask, struct rqspinlock_timeout *ts)
+{
+	if (!(atomic_read_acquire(&lock->val) & (mask)))
+		return true;
+	return false;
+}
+
+static noinline int check_deadlock_AA(rqspinlock_t *lock, u32 mask,
+				      struct rqspinlock_timeout *ts)
+{
+	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
+	int cnt = min(RES_NR_HELD, rqh->cnt);
+
+	/*
+	 * Return an error if we hold the lock we are attempting to acquire.
+	 * We'll iterate over max 32 locks; no need to do is_lock_released.
+	 */
+	for (int i = 0; i < cnt - 1; i++) {
+		if (rqh->locks[i] == lock)
+			return -EDEADLK;
+	}
+	return 0;
+}
+
+/*
+ * This focuses on the most common case of ABBA deadlocks (or ABBA involving
+ * more locks, which reduce to ABBA). This is not exhaustive, and we rely on
+ * timeouts as the final line of defense.
+ */
+static noinline int check_deadlock_ABBA(rqspinlock_t *lock, u32 mask,
+					struct rqspinlock_timeout *ts)
+{
+	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
+	int rqh_cnt = min(RES_NR_HELD, rqh->cnt);
+	void *remote_lock;
+	int cpu;
+
+	/*
+	 * Find the CPU holding the lock that we want to acquire. If there is a
+	 * deadlock scenario, we will read a stable set on the remote CPU and
+	 * find the target. This would be a constant time operation instead of
+	 * O(NR_CPUS) if we could determine the owning CPU from a lock value, but
+	 * that requires increasing the size of the lock word.
+	 */
+	for_each_possible_cpu(cpu) {
+		struct rqspinlock_held *rqh_cpu = per_cpu_ptr(&rqspinlock_held_locks, cpu);
+		int real_cnt = READ_ONCE(rqh_cpu->cnt);
+		int cnt = min(RES_NR_HELD, real_cnt);
+
+		/*
+		 * Let's ensure to break out of this loop if the lock is available for
+		 * us to potentially acquire.
+		 */
+		if (is_lock_released(lock, mask, ts))
+			return 0;
+
+		/*
+		 * Skip ourselves, and CPUs whose count is less than 2, as they need at
+		 * least one held lock and one acquisition attempt (reflected as top
+		 * most entry) to participate in an ABBA deadlock.
+		 *
+		 * If cnt is more than RES_NR_HELD, it means the current lock being
+		 * acquired won't appear in the table, and other locks in the table are
+		 * already held, so we can't determine ABBA.
+		 */
+		if (cpu == smp_processor_id() || real_cnt < 2 || real_cnt > RES_NR_HELD)
+			continue;
+
+		/*
+		 * Obtain the entry at the top, this corresponds to the lock the
+		 * remote CPU is attempting to acquire in a deadlock situation,
+		 * and would be one of the locks we hold on the current CPU.
+		 */
+		remote_lock = READ_ONCE(rqh_cpu->locks[cnt - 1]);
+		/*
+		 * If it is NULL, we've raced and cannot determine a deadlock
+		 * conclusively, skip this CPU.
+		 */
+		if (!remote_lock)
+			continue;
+		/*
+		 * Find if the lock we're attempting to acquire is held by this CPU.
+		 * Don't consider the topmost entry, as that must be the latest lock
+		 * being held or acquired.  For a deadlock, the target CPU must also
+		 * attempt to acquire a lock we hold, so for this search only 'cnt - 1'
+		 * entries are important.
+		 */
+		for (int i = 0; i < cnt - 1; i++) {
+			if (READ_ONCE(rqh_cpu->locks[i]) != lock)
+				continue;
+			/*
+			 * We found our lock as held on the remote CPU.  Is the
+			 * acquisition attempt on the remote CPU for a lock held
+			 * by us?  If so, we have a deadlock situation, and need
+			 * to recover.
+			 */
+			for (int i = 0; i < rqh_cnt - 1; i++) {
+				if (rqh->locks[i] == remote_lock)
+					return -EDEADLK;
+			}
+			/*
+			 * Inconclusive; retry again later.
+			 */
+			return 0;
+		}
+	}
+	return 0;
+}
+
+static noinline int check_deadlock(rqspinlock_t *lock, u32 mask,
+				   struct rqspinlock_timeout *ts)
+{
+	int ret;
+
+	ret = check_deadlock_AA(lock, mask, ts);
+	if (ret)
+		return ret;
+	ret = check_deadlock_ABBA(lock, mask, ts);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
+				  struct rqspinlock_timeout *ts)
 {
 	u64 time = ktime_get_mono_fast_ns();
+	u64 prev = ts->cur;
 
 	if (!ts->timeout_end) {
+		ts->cur = time;
 		ts->timeout_end = time + ts->duration;
 		return 0;
 	}
@@ -91,6 +223,15 @@ static noinline int check_timeout(struct rqspinlock_timeout *ts)
 	if (time > ts->timeout_end)
 		return -ETIMEDOUT;
 
+	/*
+	 * A millisecond interval passed from last time? Trigger deadlock
+	 * checks.
+	 */
+	if (prev + NSEC_PER_MSEC < time) {
+		ts->cur = time;
+		return check_deadlock(lock, mask, ts);
+	}
+
 	return 0;
 }
 
@@ -99,21 +240,22 @@ static noinline int check_timeout(struct rqspinlock_timeout *ts)
  * as the macro does internal amortization for us.
  */
 #ifndef res_smp_cond_load_acquire
-#define RES_CHECK_TIMEOUT(ts, ret)                    \
-	({                                            \
-		if (!(ts).spin++)                     \
-			(ret) = check_timeout(&(ts)); \
-		(ret);                                \
+#define RES_CHECK_TIMEOUT(ts, ret, mask)                              \
+	({                                                            \
+		if (!(ts).spin++)                                     \
+			(ret) = check_timeout((lock), (mask), &(ts)); \
+		(ret);                                                \
 	})
 #else
-#define RES_CHECK_TIMEOUT(ts, ret, mask)	      \
+#define RES_CHECK_TIMEOUT(ts, ret, mask)			      \
 	({ (ret) = check_timeout(&(ts)); })
 #endif
 
 /*
  * Initialize the 'spin' member.
+ * Set spin member to 0 to trigger AA/ABBA checks immediately.
  */
-#define RES_INIT_TIMEOUT(ts) ({ (ts).spin = 1; })
+#define RES_INIT_TIMEOUT(ts) ({ (ts).spin = 0; })
 
 /*
  * We only need to reset 'timeout_end', 'spin' will just wrap around as necessary.
@@ -142,6 +284,7 @@ static DEFINE_PER_CPU_ALIGNED(struct qnode, rqnodes[_Q_MAX_NODES]);
  *
  * Return:
  * * 0		- Lock was acquired successfully.
+ * * -EDEADLK	- Lock acquisition failed because of AA/ABBA deadlock.
  * * -ETIMEDOUT - Lock acquisition failed because of timeout.
  *
  * (queue tail, pending bit, lock value)
@@ -212,6 +355,11 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 		goto queue;
 	}
 
+	/*
+	 * Grab an entry in the held locks array, to enable deadlock detection.
+	 */
+	grab_held_lock_entry(lock);
+
 	/*
 	 * We're pending, wait for the owner to go away.
 	 *
@@ -225,7 +373,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 	if (val & _Q_LOCKED_MASK) {
 		RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT);
-		res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret));
+		res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_MASK));
 	}
 
 	if (ret) {
@@ -240,7 +388,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 		 */
 		clear_pending(lock);
 		lockevent_inc(rqspinlock_lock_timeout);
-		return ret;
+		goto err_release_entry;
 	}
 
 	/*
@@ -258,6 +406,11 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 queue:
 	lockevent_inc(lock_slowpath);
+	/*
+	 * Grab deadlock detection entry for the queue path.
+	 */
+	grab_held_lock_entry(lock);
+
 	node = this_cpu_ptr(&rqnodes[0].mcs);
 	idx = node->count++;
 	tail = encode_tail(smp_processor_id(), idx);
@@ -277,9 +430,9 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 		lockevent_inc(lock_no_node);
 		RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT);
 		while (!queued_spin_trylock(lock)) {
-			if (RES_CHECK_TIMEOUT(ts, ret)) {
+			if (RES_CHECK_TIMEOUT(ts, ret, ~0u)) {
 				lockevent_inc(rqspinlock_lock_timeout);
-				break;
+				goto err_release_node;
 			}
 			cpu_relax();
 		}
@@ -375,7 +528,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 	RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT * 2);
 	val = res_atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK) ||
-					   RES_CHECK_TIMEOUT(ts, ret));
+					   RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_PENDING_MASK));
 
 waitq_timeout:
 	if (ret) {
@@ -408,7 +561,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 			WRITE_ONCE(next->locked, RES_TIMEOUT_VAL);
 		}
 		lockevent_inc(rqspinlock_lock_timeout);
-		goto release;
+		goto err_release_node;
 	}
 
 	/*
@@ -455,5 +608,11 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	 */
 	__this_cpu_dec(rqnodes[0].mcs.count);
 	return ret;
+err_release_node:
+	trace_contention_end(lock, ret);
+	__this_cpu_dec(rqnodes[0].mcs.count);
+err_release_entry:
+	release_held_lock_entry();
+	return ret;
 }
 EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
-- 
2.47.1

[PATCH bpf-next v4 13/25] rqspinlock: Add a test-and-set fallback

[Kumar Kartikeya Dwivedi]

Include a test-and-set fallback when queued spinlock support is not
available. Introduce a rqspinlock type to act as a fallback when
qspinlock support is absent.

Include ifdef guards to ensure the slow path in this file is only
compiled when CONFIG_QUEUED_SPINLOCKS=y. Subsequent patches will add
further logic to ensure fallback to the test-and-set implementation
when queued spinlock support is unavailable on an architecture.

Unlike other waiting loops in rqspinlock code, the one for test-and-set
has no theoretical upper bound under contention, therefore we need a
longer timeout than usual. Bump it up to a second in this case.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/rqspinlock.h | 17 ++++++++++++
 kernel/bpf/rqspinlock.c          | 46 ++++++++++++++++++++++++++++++--
 2 files changed, 61 insertions(+), 2 deletions(-)

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 34c3dcb4299e..12f72c4a97cd 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -12,11 +12,28 @@
 #include <linux/types.h>
 #include <vdso/time64.h>
 #include <linux/percpu.h>
+#ifdef CONFIG_QUEUED_SPINLOCKS
+#include <asm/qspinlock.h>
+#endif
+
+struct rqspinlock {
+	union {
+		atomic_t val;
+		u32 locked;
+	};
+};
 
 struct qspinlock;
+#ifdef CONFIG_QUEUED_SPINLOCKS
 typedef struct qspinlock rqspinlock_t;
+#else
+typedef struct rqspinlock rqspinlock_t;
+#endif
 
+extern int resilient_tas_spin_lock(rqspinlock_t *lock);
+#ifdef CONFIG_QUEUED_SPINLOCKS
 extern int resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);
+#endif
 
 /*
  * Default timeout for waiting loops is 0.25 seconds
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index bddbcc47d38f..714dfab5caa8 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -21,7 +21,9 @@
 #include <linux/mutex.h>
 #include <linux/prefetch.h>
 #include <asm/byteorder.h>
+#ifdef CONFIG_QUEUED_SPINLOCKS
 #include <asm/qspinlock.h>
+#endif
 #include <trace/events/lock.h>
 #include <asm/rqspinlock.h>
 #include <linux/timekeeping.h>
@@ -29,9 +31,12 @@
 /*
  * Include queued spinlock definitions and statistics code
  */
+#ifdef CONFIG_QUEUED_SPINLOCKS
 #include "../locking/qspinlock.h"
 #include "../locking/lock_events.h"
 #include "rqspinlock.h"
+#include "../locking/mcs_spinlock.h"
+#endif
 
 /*
  * The basic principle of a queue-based spinlock can best be understood
@@ -70,8 +75,6 @@
  *
  */
 
-#include "../locking/mcs_spinlock.h"
-
 struct rqspinlock_timeout {
 	u64 timeout_end;
 	u64 duration;
@@ -263,6 +266,43 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
  */
 #define RES_RESET_TIMEOUT(ts, _duration) ({ (ts).timeout_end = 0; (ts).duration = _duration; })
 
+/*
+ * Provide a test-and-set fallback for cases when queued spin lock support is
+ * absent from the architecture.
+ */
+int __lockfunc resilient_tas_spin_lock(rqspinlock_t *lock)
+{
+	struct rqspinlock_timeout ts;
+	int val, ret = 0;
+
+	RES_INIT_TIMEOUT(ts);
+	grab_held_lock_entry(lock);
+
+	/*
+	 * Since the waiting loop's time is dependent on the amount of
+	 * contention, a short timeout unlike rqspinlock waiting loops
+	 * isn't enough. Choose a second as the timeout value.
+	 */
+	RES_RESET_TIMEOUT(ts, NSEC_PER_SEC);
+retry:
+	val = atomic_read(&lock->val);
+
+	if (val || !atomic_try_cmpxchg(&lock->val, &val, 1)) {
+		if (RES_CHECK_TIMEOUT(ts, ret, ~0u))
+			goto out;
+		cpu_relax();
+		goto retry;
+	}
+
+	return 0;
+out:
+	release_held_lock_entry();
+	return ret;
+}
+EXPORT_SYMBOL_GPL(resilient_tas_spin_lock);
+
+#ifdef CONFIG_QUEUED_SPINLOCKS
+
 /*
  * Per-CPU queue node structures; we can never have more than 4 nested
  * contexts: task, softirq, hardirq, nmi.
@@ -616,3 +656,5 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 	return ret;
 }
 EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
+
+#endif /* CONFIG_QUEUED_SPINLOCKS */
-- 
2.47.1

[PATCH bpf-next v4 14/25] rqspinlock: Add basic support for CONFIG_PARAVIRT

[Kumar Kartikeya Dwivedi]

We ripped out PV and virtualization related bits from rqspinlock in an
earlier commit, however, a fair lock performs poorly within a virtual
machine when the lock holder is preempted. As such, retain the
virt_spin_lock fallback to test and set lock, but with timeout and
deadlock detection. We can do this by simply depending on the
resilient_tas_spin_lock implementation from the previous patch.

We don't integrate support for CONFIG_PARAVIRT_SPINLOCKS yet, as that
requires more involved algorithmic changes and introduces more
complexity. It can be done when the need arises in the future.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 arch/x86/include/asm/rqspinlock.h | 33 +++++++++++++++++++++++++++++++
 include/asm-generic/rqspinlock.h  | 14 +++++++++++++
 kernel/bpf/rqspinlock.c           |  3 +++
 3 files changed, 50 insertions(+)
 create mode 100644 arch/x86/include/asm/rqspinlock.h

diff --git a/arch/x86/include/asm/rqspinlock.h b/arch/x86/include/asm/rqspinlock.h
new file mode 100644
index 000000000000..24a885449ee6
--- /dev/null
+++ b/arch/x86/include/asm/rqspinlock.h
@@ -0,0 +1,33 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_RQSPINLOCK_H
+#define _ASM_X86_RQSPINLOCK_H
+
+#include <asm/paravirt.h>
+
+#ifdef CONFIG_PARAVIRT
+DECLARE_STATIC_KEY_FALSE(virt_spin_lock_key);
+
+#define resilient_virt_spin_lock_enabled resilient_virt_spin_lock_enabled
+static __always_inline bool resilient_virt_spin_lock_enabled(void)
+{
+       return static_branch_likely(&virt_spin_lock_key);
+}
+
+#ifdef CONFIG_QUEUED_SPINLOCKS
+typedef struct qspinlock rqspinlock_t;
+#else
+typedef struct rqspinlock rqspinlock_t;
+#endif
+extern int resilient_tas_spin_lock(rqspinlock_t *lock);
+
+#define resilient_virt_spin_lock resilient_virt_spin_lock
+static inline int resilient_virt_spin_lock(rqspinlock_t *lock)
+{
+	return resilient_tas_spin_lock(lock);
+}
+
+#endif /* CONFIG_PARAVIRT */
+
+#include <asm-generic/rqspinlock.h>
+
+#endif /* _ASM_X86_RQSPINLOCK_H */
diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 12f72c4a97cd..a837c6b6abd9 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -35,6 +35,20 @@ extern int resilient_tas_spin_lock(rqspinlock_t *lock);
 extern int resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val);
 #endif
 
+#ifndef resilient_virt_spin_lock_enabled
+static __always_inline bool resilient_virt_spin_lock_enabled(void)
+{
+	return false;
+}
+#endif
+
+#ifndef resilient_virt_spin_lock
+static __always_inline int resilient_virt_spin_lock(rqspinlock_t *lock)
+{
+	return 0;
+}
+#endif
+
 /*
  * Default timeout for waiting loops is 0.25 seconds
  */
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index 714dfab5caa8..ed21ee010063 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -352,6 +352,9 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 
 	BUILD_BUG_ON(CONFIG_NR_CPUS >= (1U << _Q_TAIL_CPU_BITS));
 
+	if (resilient_virt_spin_lock_enabled())
+		return resilient_virt_spin_lock(lock);
+
 	RES_INIT_TIMEOUT(ts);
 
 	/*
-- 
2.47.1

[PATCH bpf-next v4 15/25] rqspinlock: Add helper to print a splat on timeout or deadlock

[Kumar Kartikeya Dwivedi]

Whenever a timeout and a deadlock occurs, we would want to print a
message to the dmesg console, including the CPU where the event
occurred, the list of locks in the held locks table, and the stack trace
of the caller, which allows determining where exactly in the slow path
the waiter timed out or detected a deadlock.

Splats are limited to atmost one per-CPU during machine uptime, and a
lock is acquired to ensure that no interleaving occurs when a concurrent
set of CPUs conflict and enter a deadlock situation and start printing
data.

Later patches will use this to inspect return value of rqspinlock API
and then report a violation if necessary.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/rqspinlock.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index ed21ee010063..ad0fc35c647e 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -196,6 +196,35 @@ static noinline int check_deadlock_ABBA(rqspinlock_t *lock, u32 mask,
 	return 0;
 }
 
+static DEFINE_PER_CPU(int, report_nest_cnt);
+static DEFINE_PER_CPU(bool, report_flag);
+static arch_spinlock_t report_lock;
+
+static void rqspinlock_report_violation(const char *s, void *lock)
+{
+	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
+
+	if (this_cpu_inc_return(report_nest_cnt) != 1) {
+		this_cpu_dec(report_nest_cnt);
+		return;
+	}
+	if (this_cpu_read(report_flag))
+		goto end;
+	this_cpu_write(report_flag, true);
+	arch_spin_lock(&report_lock);
+
+	pr_err("CPU %d: %s", smp_processor_id(), s);
+	pr_info("Held locks: %d\n", rqh->cnt + 1);
+	pr_info("Held lock[%2d] = 0x%px\n", 0, lock);
+	for (int i = 0; i < min(RES_NR_HELD, rqh->cnt); i++)
+		pr_info("Held lock[%2d] = 0x%px\n", i + 1, rqh->locks[i]);
+	dump_stack();
+
+	arch_spin_unlock(&report_lock);
+end:
+	this_cpu_dec(report_nest_cnt);
+}
+
 static noinline int check_deadlock(rqspinlock_t *lock, u32 mask,
 				   struct rqspinlock_timeout *ts)
 {
-- 
2.47.1

[PATCH bpf-next v4 16/25] rqspinlock: Add macros for rqspinlock usage

[Kumar Kartikeya Dwivedi]

Introduce helper macros that wrap around the rqspinlock slow path and
provide an interface analogous to the raw_spin_lock API. Note that
in case of error conditions, preemption and IRQ disabling is
automatically unrolled before returning the error back to the caller.

Ensure that in absence of CONFIG_QUEUED_SPINLOCKS support, we fallback
to the test-and-set implementation.

Add some comments describing the subtle memory ordering logic during
unlock, and why it's safe.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/rqspinlock.h | 87 ++++++++++++++++++++++++++++++++
 1 file changed, 87 insertions(+)

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index a837c6b6abd9..23abd0b8d0f9 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -153,4 +153,91 @@ static __always_inline void release_held_lock_entry(void)
 	this_cpu_dec(rqspinlock_held_locks.cnt);
 }
 
+#ifdef CONFIG_QUEUED_SPINLOCKS
+
+/**
+ * res_spin_lock - acquire a queued spinlock
+ * @lock: Pointer to queued spinlock structure
+ *
+ * Return:
+ * * 0		- Lock was acquired successfully.
+ * * -EDEADLK	- Lock acquisition failed because of AA/ABBA deadlock.
+ * * -ETIMEDOUT - Lock acquisition failed because of timeout.
+ */
+static __always_inline int res_spin_lock(rqspinlock_t *lock)
+{
+	int val = 0;
+
+	if (likely(atomic_try_cmpxchg_acquire(&lock->val, &val, _Q_LOCKED_VAL))) {
+		grab_held_lock_entry(lock);
+		return 0;
+	}
+	return resilient_queued_spin_lock_slowpath(lock, val);
+}
+
+#else
+
+#define res_spin_lock(lock) resilient_tas_spin_lock(lock)
+
+#endif /* CONFIG_QUEUED_SPINLOCKS */
+
+static __always_inline void res_spin_unlock(rqspinlock_t *lock)
+{
+	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
+
+	if (unlikely(rqh->cnt > RES_NR_HELD))
+		goto unlock;
+	WRITE_ONCE(rqh->locks[rqh->cnt - 1], NULL);
+unlock:
+	/*
+	 * Release barrier, ensures correct ordering. See release_held_lock_entry
+	 * for details.  Perform release store instead of queued_spin_unlock,
+	 * since we use this function for test-and-set fallback as well. When we
+	 * have CONFIG_QUEUED_SPINLOCKS=n, we clear the full 4-byte lockword.
+	 *
+	 * Like release_held_lock_entry, we can do the release before the dec.
+	 * We simply care about not seeing the 'lock' in our table from a remote
+	 * CPU once the lock has been released, which doesn't rely on the dec.
+	 *
+	 * Unlike smp_wmb(), release is not a two way fence, hence it is
+	 * possible for a inc to move up and reorder with our clearing of the
+	 * entry. This isn't a problem however, as for a misdiagnosis of ABBA,
+	 * the remote CPU needs to hold this lock, which won't be released until
+	 * the store below is done, which would ensure the entry is overwritten
+	 * to NULL, etc.
+	 */
+	smp_store_release(&lock->locked, 0);
+	this_cpu_dec(rqspinlock_held_locks.cnt);
+}
+
+#ifdef CONFIG_QUEUED_SPINLOCKS
+#define raw_res_spin_lock_init(lock) ({ *(lock) = (rqspinlock_t)__ARCH_SPIN_LOCK_UNLOCKED; })
+#else
+#define raw_res_spin_lock_init(lock) ({ *(lock) = (rqspinlock_t){0}; })
+#endif
+
+#define raw_res_spin_lock(lock)                    \
+	({                                         \
+		int __ret;                         \
+		preempt_disable();                 \
+		__ret = res_spin_lock(lock);	   \
+		if (__ret)                         \
+			preempt_enable();          \
+		__ret;                             \
+	})
+
+#define raw_res_spin_unlock(lock) ({ res_spin_unlock(lock); preempt_enable(); })
+
+#define raw_res_spin_lock_irqsave(lock, flags)    \
+	({                                        \
+		int __ret;                        \
+		local_irq_save(flags);            \
+		__ret = raw_res_spin_lock(lock);  \
+		if (__ret)                        \
+			local_irq_restore(flags); \
+		__ret;                            \
+	})
+
+#define raw_res_spin_unlock_irqrestore(lock, flags) ({ raw_res_spin_unlock(lock); local_irq_restore(flags); })
+
 #endif /* __ASM_GENERIC_RQSPINLOCK_H */
-- 
2.47.1

[PATCH bpf-next v4 17/25] rqspinlock: Add entry to Makefile, MAINTAINERS

[Kumar Kartikeya Dwivedi]

Ensure that the rqspinlock code is only built when the BPF subsystem is
compiled in. Depending on queued spinlock support, we may or may not end
up building the queued spinlock slowpath, and instead fallback to the
test-and-set implementation. Also add entries to MAINTAINERS file.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 MAINTAINERS                | 2 ++
 include/asm-generic/Kbuild | 1 +
 kernel/bpf/Makefile        | 2 +-
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index 3864d473f52f..c545cd149cd1 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4297,6 +4297,8 @@ F:	include/uapi/linux/filter.h
 F:	kernel/bpf/
 F:	kernel/trace/bpf_trace.c
 F:	lib/buildid.c
+F:	arch/*/include/asm/rqspinlock.h
+F:	include/asm-generic/rqspinlock.h
 F:	lib/test_bpf.c
 F:	net/bpf/
 F:	net/core/filter.c
diff --git a/include/asm-generic/Kbuild b/include/asm-generic/Kbuild
index 1b43c3a77012..8675b7b4ad23 100644
--- a/include/asm-generic/Kbuild
+++ b/include/asm-generic/Kbuild
@@ -45,6 +45,7 @@ mandatory-y += pci.h
 mandatory-y += percpu.h
 mandatory-y += pgalloc.h
 mandatory-y += preempt.h
+mandatory-y += rqspinlock.h
 mandatory-y += runtime-const.h
 mandatory-y += rwonce.h
 mandatory-y += sections.h
diff --git a/kernel/bpf/Makefile b/kernel/bpf/Makefile
index 410028633621..70502f038b92 100644
--- a/kernel/bpf/Makefile
+++ b/kernel/bpf/Makefile
@@ -14,7 +14,7 @@ obj-$(CONFIG_BPF_SYSCALL) += bpf_local_storage.o bpf_task_storage.o
 obj-${CONFIG_BPF_LSM}	  += bpf_inode_storage.o
 obj-$(CONFIG_BPF_SYSCALL) += disasm.o mprog.o
 obj-$(CONFIG_BPF_JIT) += trampoline.o
-obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o
+obj-$(CONFIG_BPF_SYSCALL) += btf.o memalloc.o rqspinlock.o
 ifeq ($(CONFIG_MMU)$(CONFIG_64BIT),yy)
 obj-$(CONFIG_BPF_SYSCALL) += arena.o range_tree.o
 endif
-- 
2.47.1

[PATCH bpf-next v4 18/25] rqspinlock: Add locktorture support

[Kumar Kartikeya Dwivedi]

Introduce locktorture support for rqspinlock using the newly added
macros as the first in-kernel user and consumer. Guard the code with
CONFIG_BPF_SYSCALL ifdef since rqspinlock is not available otherwise.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/locking/locktorture.c | 57 ++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/kernel/locking/locktorture.c b/kernel/locking/locktorture.c
index cc33470f4de9..ce0362f0a871 100644
--- a/kernel/locking/locktorture.c
+++ b/kernel/locking/locktorture.c
@@ -362,6 +362,60 @@ static struct lock_torture_ops raw_spin_lock_irq_ops = {
 	.name		= "raw_spin_lock_irq"
 };
 
+#ifdef CONFIG_BPF_SYSCALL
+
+#include <asm/rqspinlock.h>
+static rqspinlock_t rqspinlock;
+
+static int torture_raw_res_spin_write_lock(int tid __maybe_unused)
+{
+	raw_res_spin_lock(&rqspinlock);
+	return 0;
+}
+
+static void torture_raw_res_spin_write_unlock(int tid __maybe_unused)
+{
+	raw_res_spin_unlock(&rqspinlock);
+}
+
+static struct lock_torture_ops raw_res_spin_lock_ops = {
+	.writelock	= torture_raw_res_spin_write_lock,
+	.write_delay	= torture_spin_lock_write_delay,
+	.task_boost     = torture_rt_boost,
+	.writeunlock	= torture_raw_res_spin_write_unlock,
+	.readlock       = NULL,
+	.read_delay     = NULL,
+	.readunlock     = NULL,
+	.name		= "raw_res_spin_lock"
+};
+
+static int torture_raw_res_spin_write_lock_irq(int tid __maybe_unused)
+{
+	unsigned long flags;
+
+	raw_res_spin_lock_irqsave(&rqspinlock, flags);
+	cxt.cur_ops->flags = flags;
+	return 0;
+}
+
+static void torture_raw_res_spin_write_unlock_irq(int tid __maybe_unused)
+{
+	raw_res_spin_unlock_irqrestore(&rqspinlock, cxt.cur_ops->flags);
+}
+
+static struct lock_torture_ops raw_res_spin_lock_irq_ops = {
+	.writelock	= torture_raw_res_spin_write_lock_irq,
+	.write_delay	= torture_spin_lock_write_delay,
+	.task_boost     = torture_rt_boost,
+	.writeunlock	= torture_raw_res_spin_write_unlock_irq,
+	.readlock       = NULL,
+	.read_delay     = NULL,
+	.readunlock     = NULL,
+	.name		= "raw_res_spin_lock_irq"
+};
+
+#endif
+
 static DEFINE_RWLOCK(torture_rwlock);
 
 static int torture_rwlock_write_lock(int tid __maybe_unused)
@@ -1168,6 +1222,9 @@ static int __init lock_torture_init(void)
 		&lock_busted_ops,
 		&spin_lock_ops, &spin_lock_irq_ops,
 		&raw_spin_lock_ops, &raw_spin_lock_irq_ops,
+#ifdef CONFIG_BPF_SYSCALL
+		&raw_res_spin_lock_ops, &raw_res_spin_lock_irq_ops,
+#endif
 		&rw_lock_ops, &rw_lock_irq_ops,
 		&mutex_lock_ops,
 		&ww_mutex_lock_ops,
-- 
2.47.1

[PATCH bpf-next v4 19/25] bpf: Convert hashtab.c to rqspinlock

[Kumar Kartikeya Dwivedi]

Convert hashtab.c from raw_spinlock to rqspinlock, and drop the hashed
per-cpu counter crud from the code base which is no longer necessary.

Closes: https://lore.kernel.org/bpf/675302fd.050a0220.2477f.0004.GAE@google.com
Closes: https://lore.kernel.org/bpf/000000000000b3e63e061eed3f6b@google.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/hashtab.c | 102 ++++++++++++++-----------------------------
 1 file changed, 32 insertions(+), 70 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 877298133fda..5a5adc66b8e2 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -16,6 +16,7 @@
 #include "bpf_lru_list.h"
 #include "map_in_map.h"
 #include <linux/bpf_mem_alloc.h>
+#include <asm/rqspinlock.h>
 
 #define HTAB_CREATE_FLAG_MASK						\
 	(BPF_F_NO_PREALLOC | BPF_F_NO_COMMON_LRU | BPF_F_NUMA_NODE |	\
@@ -78,7 +79,7 @@
  */
 struct bucket {
 	struct hlist_nulls_head head;
-	raw_spinlock_t raw_lock;
+	rqspinlock_t raw_lock;
 };
 
 #define HASHTAB_MAP_LOCK_COUNT 8
@@ -104,8 +105,6 @@ struct bpf_htab {
 	u32 n_buckets;	/* number of hash buckets */
 	u32 elem_size;	/* size of each element in bytes */
 	u32 hashrnd;
-	struct lock_class_key lockdep_key;
-	int __percpu *map_locked[HASHTAB_MAP_LOCK_COUNT];
 };
 
 /* each htab element is struct htab_elem + key + value */
@@ -140,45 +139,26 @@ static void htab_init_buckets(struct bpf_htab *htab)
 
 	for (i = 0; i < htab->n_buckets; i++) {
 		INIT_HLIST_NULLS_HEAD(&htab->buckets[i].head, i);
-		raw_spin_lock_init(&htab->buckets[i].raw_lock);
-		lockdep_set_class(&htab->buckets[i].raw_lock,
-					  &htab->lockdep_key);
+		raw_res_spin_lock_init(&htab->buckets[i].raw_lock);
 		cond_resched();
 	}
 }
 
-static inline int htab_lock_bucket(const struct bpf_htab *htab,
-				   struct bucket *b, u32 hash,
-				   unsigned long *pflags)
+static inline int htab_lock_bucket(struct bucket *b, unsigned long *pflags)
 {
 	unsigned long flags;
+	int ret;
 
-	hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
-
-	preempt_disable();
-	local_irq_save(flags);
-	if (unlikely(__this_cpu_inc_return(*(htab->map_locked[hash])) != 1)) {
-		__this_cpu_dec(*(htab->map_locked[hash]));
-		local_irq_restore(flags);
-		preempt_enable();
-		return -EBUSY;
-	}
-
-	raw_spin_lock(&b->raw_lock);
+	ret = raw_res_spin_lock_irqsave(&b->raw_lock, flags);
+	if (ret)
+		return ret;
 	*pflags = flags;
-
 	return 0;
 }
 
-static inline void htab_unlock_bucket(const struct bpf_htab *htab,
-				      struct bucket *b, u32 hash,
-				      unsigned long flags)
+static inline void htab_unlock_bucket(struct bucket *b, unsigned long flags)
 {
-	hash = hash & min_t(u32, HASHTAB_MAP_LOCK_MASK, htab->n_buckets - 1);
-	raw_spin_unlock(&b->raw_lock);
-	__this_cpu_dec(*(htab->map_locked[hash]));
-	local_irq_restore(flags);
-	preempt_enable();
+	raw_res_spin_unlock_irqrestore(&b->raw_lock, flags);
 }
 
 static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node);
@@ -483,14 +463,12 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	bool percpu_lru = (attr->map_flags & BPF_F_NO_COMMON_LRU);
 	bool prealloc = !(attr->map_flags & BPF_F_NO_PREALLOC);
 	struct bpf_htab *htab;
-	int err, i;
+	int err;
 
 	htab = bpf_map_area_alloc(sizeof(*htab), NUMA_NO_NODE);
 	if (!htab)
 		return ERR_PTR(-ENOMEM);
 
-	lockdep_register_key(&htab->lockdep_key);
-
 	bpf_map_init_from_attr(&htab->map, attr);
 
 	if (percpu_lru) {
@@ -536,15 +514,6 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 	if (!htab->buckets)
 		goto free_elem_count;
 
-	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++) {
-		htab->map_locked[i] = bpf_map_alloc_percpu(&htab->map,
-							   sizeof(int),
-							   sizeof(int),
-							   GFP_USER);
-		if (!htab->map_locked[i])
-			goto free_map_locked;
-	}
-
 	if (htab->map.map_flags & BPF_F_ZERO_SEED)
 		htab->hashrnd = 0;
 	else
@@ -607,15 +576,12 @@ static struct bpf_map *htab_map_alloc(union bpf_attr *attr)
 free_map_locked:
 	if (htab->use_percpu_counter)
 		percpu_counter_destroy(&htab->pcount);
-	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
-		free_percpu(htab->map_locked[i]);
 	bpf_map_area_free(htab->buckets);
 	bpf_mem_alloc_destroy(&htab->pcpu_ma);
 	bpf_mem_alloc_destroy(&htab->ma);
 free_elem_count:
 	bpf_map_free_elem_count(&htab->map);
 free_htab:
-	lockdep_unregister_key(&htab->lockdep_key);
 	bpf_map_area_free(htab);
 	return ERR_PTR(err);
 }
@@ -820,7 +786,7 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
 	b = __select_bucket(htab, tgt_l->hash);
 	head = &b->head;
 
-	ret = htab_lock_bucket(htab, b, tgt_l->hash, &flags);
+	ret = htab_lock_bucket(b, &flags);
 	if (ret)
 		return false;
 
@@ -831,7 +797,7 @@ static bool htab_lru_map_delete_node(void *arg, struct bpf_lru_node *node)
 			break;
 		}
 
-	htab_unlock_bucket(htab, b, tgt_l->hash, flags);
+	htab_unlock_bucket(b, flags);
 
 	if (l == tgt_l)
 		check_and_free_fields(htab, l);
@@ -1150,7 +1116,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 		 */
 	}
 
-	ret = htab_lock_bucket(htab, b, hash, &flags);
+	ret = htab_lock_bucket(b, &flags);
 	if (ret)
 		return ret;
 
@@ -1201,7 +1167,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 			check_and_free_fields(htab, l_old);
 		}
 	}
-	htab_unlock_bucket(htab, b, hash, flags);
+	htab_unlock_bucket(b, flags);
 	if (l_old) {
 		if (old_map_ptr)
 			map->ops->map_fd_put_ptr(map, old_map_ptr, true);
@@ -1210,7 +1176,7 @@ static long htab_map_update_elem(struct bpf_map *map, void *key, void *value,
 	}
 	return 0;
 err:
-	htab_unlock_bucket(htab, b, hash, flags);
+	htab_unlock_bucket(b, flags);
 	return ret;
 }
 
@@ -1257,7 +1223,7 @@ static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value
 	copy_map_value(&htab->map,
 		       l_new->key + round_up(map->key_size, 8), value);
 
-	ret = htab_lock_bucket(htab, b, hash, &flags);
+	ret = htab_lock_bucket(b, &flags);
 	if (ret)
 		goto err_lock_bucket;
 
@@ -1278,7 +1244,7 @@ static long htab_lru_map_update_elem(struct bpf_map *map, void *key, void *value
 	ret = 0;
 
 err:
-	htab_unlock_bucket(htab, b, hash, flags);
+	htab_unlock_bucket(b, flags);
 
 err_lock_bucket:
 	if (ret)
@@ -1315,7 +1281,7 @@ static long __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
 	b = __select_bucket(htab, hash);
 	head = &b->head;
 
-	ret = htab_lock_bucket(htab, b, hash, &flags);
+	ret = htab_lock_bucket(b, &flags);
 	if (ret)
 		return ret;
 
@@ -1340,7 +1306,7 @@ static long __htab_percpu_map_update_elem(struct bpf_map *map, void *key,
 	}
 	ret = 0;
 err:
-	htab_unlock_bucket(htab, b, hash, flags);
+	htab_unlock_bucket(b, flags);
 	return ret;
 }
 
@@ -1381,7 +1347,7 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
 			return -ENOMEM;
 	}
 
-	ret = htab_lock_bucket(htab, b, hash, &flags);
+	ret = htab_lock_bucket(b, &flags);
 	if (ret)
 		goto err_lock_bucket;
 
@@ -1405,7 +1371,7 @@ static long __htab_lru_percpu_map_update_elem(struct bpf_map *map, void *key,
 	}
 	ret = 0;
 err:
-	htab_unlock_bucket(htab, b, hash, flags);
+	htab_unlock_bucket(b, flags);
 err_lock_bucket:
 	if (l_new) {
 		bpf_map_dec_elem_count(&htab->map);
@@ -1447,7 +1413,7 @@ static long htab_map_delete_elem(struct bpf_map *map, void *key)
 	b = __select_bucket(htab, hash);
 	head = &b->head;
 
-	ret = htab_lock_bucket(htab, b, hash, &flags);
+	ret = htab_lock_bucket(b, &flags);
 	if (ret)
 		return ret;
 
@@ -1457,7 +1423,7 @@ static long htab_map_delete_elem(struct bpf_map *map, void *key)
 	else
 		ret = -ENOENT;
 
-	htab_unlock_bucket(htab, b, hash, flags);
+	htab_unlock_bucket(b, flags);
 
 	if (l)
 		free_htab_elem(htab, l);
@@ -1483,7 +1449,7 @@ static long htab_lru_map_delete_elem(struct bpf_map *map, void *key)
 	b = __select_bucket(htab, hash);
 	head = &b->head;
 
-	ret = htab_lock_bucket(htab, b, hash, &flags);
+	ret = htab_lock_bucket(b, &flags);
 	if (ret)
 		return ret;
 
@@ -1494,7 +1460,7 @@ static long htab_lru_map_delete_elem(struct bpf_map *map, void *key)
 	else
 		ret = -ENOENT;
 
-	htab_unlock_bucket(htab, b, hash, flags);
+	htab_unlock_bucket(b, flags);
 	if (l)
 		htab_lru_push_free(htab, l);
 	return ret;
@@ -1561,7 +1527,6 @@ static void htab_map_free_timers_and_wq(struct bpf_map *map)
 static void htab_map_free(struct bpf_map *map)
 {
 	struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
-	int i;
 
 	/* bpf_free_used_maps() or close(map_fd) will trigger this map_free callback.
 	 * bpf_free_used_maps() is called after bpf prog is no longer executing.
@@ -1586,9 +1551,6 @@ static void htab_map_free(struct bpf_map *map)
 	bpf_mem_alloc_destroy(&htab->ma);
 	if (htab->use_percpu_counter)
 		percpu_counter_destroy(&htab->pcount);
-	for (i = 0; i < HASHTAB_MAP_LOCK_COUNT; i++)
-		free_percpu(htab->map_locked[i]);
-	lockdep_unregister_key(&htab->lockdep_key);
 	bpf_map_area_free(htab);
 }
 
@@ -1631,7 +1593,7 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
 	b = __select_bucket(htab, hash);
 	head = &b->head;
 
-	ret = htab_lock_bucket(htab, b, hash, &bflags);
+	ret = htab_lock_bucket(b, &bflags);
 	if (ret)
 		return ret;
 
@@ -1668,7 +1630,7 @@ static int __htab_map_lookup_and_delete_elem(struct bpf_map *map, void *key,
 	hlist_nulls_del_rcu(&l->hash_node);
 
 out_unlock:
-	htab_unlock_bucket(htab, b, hash, bflags);
+	htab_unlock_bucket(b, bflags);
 
 	if (l) {
 		if (is_lru_map)
@@ -1790,7 +1752,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 	head = &b->head;
 	/* do not grab the lock unless need it (bucket_cnt > 0). */
 	if (locked) {
-		ret = htab_lock_bucket(htab, b, batch, &flags);
+		ret = htab_lock_bucket(b, &flags);
 		if (ret) {
 			rcu_read_unlock();
 			bpf_enable_instrumentation();
@@ -1813,7 +1775,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 		/* Note that since bucket_cnt > 0 here, it is implicit
 		 * that the locked was grabbed, so release it.
 		 */
-		htab_unlock_bucket(htab, b, batch, flags);
+		htab_unlock_bucket(b, flags);
 		rcu_read_unlock();
 		bpf_enable_instrumentation();
 		goto after_loop;
@@ -1824,7 +1786,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 		/* Note that since bucket_cnt > 0 here, it is implicit
 		 * that the locked was grabbed, so release it.
 		 */
-		htab_unlock_bucket(htab, b, batch, flags);
+		htab_unlock_bucket(b, flags);
 		rcu_read_unlock();
 		bpf_enable_instrumentation();
 		kvfree(keys);
@@ -1887,7 +1849,7 @@ __htab_map_lookup_and_delete_batch(struct bpf_map *map,
 		dst_val += value_size;
 	}
 
-	htab_unlock_bucket(htab, b, batch, flags);
+	htab_unlock_bucket(b, flags);
 	locked = false;
 
 	while (node_to_free) {
-- 
2.47.1

[PATCH bpf-next v4 20/25] bpf: Convert percpu_freelist.c to rqspinlock

[Kumar Kartikeya Dwivedi]

Convert the percpu_freelist.c code to use rqspinlock, and remove the
extralist fallback and trylock-based acquisitions to avoid deadlocks.

Key thing to note is the retained while (true) loop to search through
other CPUs when failing to push a node due to locking errors. This
retains the behavior of the old code, where it would keep trying until
it would be able to successfully push the node back into the freelist of
a CPU.

Technically, we should start iteration for this loop from
raw_smp_processor_id() + 1, but to avoid hitting the edge of nr_cpus,
we skip execution in the loop body instead.

Closes: https://lore.kernel.org/bpf/CAPPBnEa1_pZ6W24+WwtcNFvTUHTHO7KUmzEbOcMqxp+m2o15qQ@mail.gmail.com
Closes: https://lore.kernel.org/bpf/CAPPBnEYm+9zduStsZaDnq93q1jPLqO-PiKX9jy0MuL8LCXmCrQ@mail.gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/percpu_freelist.c | 113 ++++++++---------------------------
 kernel/bpf/percpu_freelist.h |   4 +-
 2 files changed, 27 insertions(+), 90 deletions(-)

diff --git a/kernel/bpf/percpu_freelist.c b/kernel/bpf/percpu_freelist.c
index 034cf87b54e9..632762b57299 100644
--- a/kernel/bpf/percpu_freelist.c
+++ b/kernel/bpf/percpu_freelist.c
@@ -14,11 +14,9 @@ int pcpu_freelist_init(struct pcpu_freelist *s)
 	for_each_possible_cpu(cpu) {
 		struct pcpu_freelist_head *head = per_cpu_ptr(s->freelist, cpu);
 
-		raw_spin_lock_init(&head->lock);
+		raw_res_spin_lock_init(&head->lock);
 		head->first = NULL;
 	}
-	raw_spin_lock_init(&s->extralist.lock);
-	s->extralist.first = NULL;
 	return 0;
 }
 
@@ -34,58 +32,39 @@ static inline void pcpu_freelist_push_node(struct pcpu_freelist_head *head,
 	WRITE_ONCE(head->first, node);
 }
 
-static inline void ___pcpu_freelist_push(struct pcpu_freelist_head *head,
+static inline bool ___pcpu_freelist_push(struct pcpu_freelist_head *head,
 					 struct pcpu_freelist_node *node)
 {
-	raw_spin_lock(&head->lock);
-	pcpu_freelist_push_node(head, node);
-	raw_spin_unlock(&head->lock);
-}
-
-static inline bool pcpu_freelist_try_push_extra(struct pcpu_freelist *s,
-						struct pcpu_freelist_node *node)
-{
-	if (!raw_spin_trylock(&s->extralist.lock))
+	if (raw_res_spin_lock(&head->lock))
 		return false;
-
-	pcpu_freelist_push_node(&s->extralist, node);
-	raw_spin_unlock(&s->extralist.lock);
+	pcpu_freelist_push_node(head, node);
+	raw_res_spin_unlock(&head->lock);
 	return true;
 }
 
-static inline void ___pcpu_freelist_push_nmi(struct pcpu_freelist *s,
-					     struct pcpu_freelist_node *node)
+void __pcpu_freelist_push(struct pcpu_freelist *s,
+			struct pcpu_freelist_node *node)
 {
-	int cpu, orig_cpu;
+	struct pcpu_freelist_head *head;
+	int cpu;
 
-	orig_cpu = raw_smp_processor_id();
-	while (1) {
-		for_each_cpu_wrap(cpu, cpu_possible_mask, orig_cpu) {
-			struct pcpu_freelist_head *head;
+	if (___pcpu_freelist_push(this_cpu_ptr(s->freelist), node))
+		return;
 
+	while (true) {
+		for_each_cpu_wrap(cpu, cpu_possible_mask, raw_smp_processor_id()) {
+			if (cpu == raw_smp_processor_id())
+				continue;
 			head = per_cpu_ptr(s->freelist, cpu);
-			if (raw_spin_trylock(&head->lock)) {
-				pcpu_freelist_push_node(head, node);
-				raw_spin_unlock(&head->lock);
-				return;
-			}
-		}
-
-		/* cannot lock any per cpu lock, try extralist */
-		if (pcpu_freelist_try_push_extra(s, node))
+			if (raw_res_spin_lock(&head->lock))
+				continue;
+			pcpu_freelist_push_node(head, node);
+			raw_res_spin_unlock(&head->lock);
 			return;
+		}
 	}
 }
 
-void __pcpu_freelist_push(struct pcpu_freelist *s,
-			struct pcpu_freelist_node *node)
-{
-	if (in_nmi())
-		___pcpu_freelist_push_nmi(s, node);
-	else
-		___pcpu_freelist_push(this_cpu_ptr(s->freelist), node);
-}
-
 void pcpu_freelist_push(struct pcpu_freelist *s,
 			struct pcpu_freelist_node *node)
 {
@@ -120,71 +99,29 @@ void pcpu_freelist_populate(struct pcpu_freelist *s, void *buf, u32 elem_size,
 
 static struct pcpu_freelist_node *___pcpu_freelist_pop(struct pcpu_freelist *s)
 {
+	struct pcpu_freelist_node *node = NULL;
 	struct pcpu_freelist_head *head;
-	struct pcpu_freelist_node *node;
 	int cpu;
 
 	for_each_cpu_wrap(cpu, cpu_possible_mask, raw_smp_processor_id()) {
 		head = per_cpu_ptr(s->freelist, cpu);
 		if (!READ_ONCE(head->first))
 			continue;
-		raw_spin_lock(&head->lock);
+		if (raw_res_spin_lock(&head->lock))
+			continue;
 		node = head->first;
 		if (node) {
 			WRITE_ONCE(head->first, node->next);
-			raw_spin_unlock(&head->lock);
+			raw_res_spin_unlock(&head->lock);
 			return node;
 		}
-		raw_spin_unlock(&head->lock);
+		raw_res_spin_unlock(&head->lock);
 	}
-
-	/* per cpu lists are all empty, try extralist */
-	if (!READ_ONCE(s->extralist.first))
-		return NULL;
-	raw_spin_lock(&s->extralist.lock);
-	node = s->extralist.first;
-	if (node)
-		WRITE_ONCE(s->extralist.first, node->next);
-	raw_spin_unlock(&s->extralist.lock);
-	return node;
-}
-
-static struct pcpu_freelist_node *
-___pcpu_freelist_pop_nmi(struct pcpu_freelist *s)
-{
-	struct pcpu_freelist_head *head;
-	struct pcpu_freelist_node *node;
-	int cpu;
-
-	for_each_cpu_wrap(cpu, cpu_possible_mask, raw_smp_processor_id()) {
-		head = per_cpu_ptr(s->freelist, cpu);
-		if (!READ_ONCE(head->first))
-			continue;
-		if (raw_spin_trylock(&head->lock)) {
-			node = head->first;
-			if (node) {
-				WRITE_ONCE(head->first, node->next);
-				raw_spin_unlock(&head->lock);
-				return node;
-			}
-			raw_spin_unlock(&head->lock);
-		}
-	}
-
-	/* cannot pop from per cpu lists, try extralist */
-	if (!READ_ONCE(s->extralist.first) || !raw_spin_trylock(&s->extralist.lock))
-		return NULL;
-	node = s->extralist.first;
-	if (node)
-		WRITE_ONCE(s->extralist.first, node->next);
-	raw_spin_unlock(&s->extralist.lock);
 	return node;
 }
 
 struct pcpu_freelist_node *__pcpu_freelist_pop(struct pcpu_freelist *s)
 {
-	if (in_nmi())
-		return ___pcpu_freelist_pop_nmi(s);
 	return ___pcpu_freelist_pop(s);
 }
 
diff --git a/kernel/bpf/percpu_freelist.h b/kernel/bpf/percpu_freelist.h
index 3c76553cfe57..914798b74967 100644
--- a/kernel/bpf/percpu_freelist.h
+++ b/kernel/bpf/percpu_freelist.h
@@ -5,15 +5,15 @@
 #define __PERCPU_FREELIST_H__
 #include <linux/spinlock.h>
 #include <linux/percpu.h>
+#include <asm/rqspinlock.h>
 
 struct pcpu_freelist_head {
 	struct pcpu_freelist_node *first;
-	raw_spinlock_t lock;
+	rqspinlock_t lock;
 };
 
 struct pcpu_freelist {
 	struct pcpu_freelist_head __percpu *freelist;
-	struct pcpu_freelist_head extralist;
 };
 
 struct pcpu_freelist_node {
-- 
2.47.1

[PATCH bpf-next v4 21/25] bpf: Convert lpm_trie.c to rqspinlock

[Kumar Kartikeya Dwivedi]

Convert all LPM trie usage of raw_spinlock to rqspinlock.

Note that rcu_dereference_protected in trie_delete_elem is switched over
to plain rcu_dereference, the RCU read lock should be held from BPF
program side or eBPF syscall path, and the trie->lock is just acquired
before the dereference. It is not clear the reason the protected variant
was used from the commit history, but the above reasoning makes sense so
switch over.

Closes: https://lore.kernel.org/lkml/000000000000adb08b061413919e@google.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 kernel/bpf/lpm_trie.c | 25 ++++++++++++++-----------
 1 file changed, 14 insertions(+), 11 deletions(-)

diff --git a/kernel/bpf/lpm_trie.c b/kernel/bpf/lpm_trie.c
index e8a772e64324..be66d7e520e0 100644
--- a/kernel/bpf/lpm_trie.c
+++ b/kernel/bpf/lpm_trie.c
@@ -15,6 +15,7 @@
 #include <net/ipv6.h>
 #include <uapi/linux/btf.h>
 #include <linux/btf_ids.h>
+#include <asm/rqspinlock.h>
 #include <linux/bpf_mem_alloc.h>
 
 /* Intermediate node */
@@ -36,7 +37,7 @@ struct lpm_trie {
 	size_t				n_entries;
 	size_t				max_prefixlen;
 	size_t				data_size;
-	raw_spinlock_t			lock;
+	rqspinlock_t			lock;
 };
 
 /* This trie implements a longest prefix match algorithm that can be used to
@@ -342,7 +343,9 @@ static long trie_update_elem(struct bpf_map *map,
 	if (!new_node)
 		return -ENOMEM;
 
-	raw_spin_lock_irqsave(&trie->lock, irq_flags);
+	ret = raw_res_spin_lock_irqsave(&trie->lock, irq_flags);
+	if (ret)
+		goto out_free;
 
 	new_node->prefixlen = key->prefixlen;
 	RCU_INIT_POINTER(new_node->child[0], NULL);
@@ -356,8 +359,7 @@ static long trie_update_elem(struct bpf_map *map,
 	 */
 	slot = &trie->root;
 
-	while ((node = rcu_dereference_protected(*slot,
-					lockdep_is_held(&trie->lock)))) {
+	while ((node = rcu_dereference(*slot))) {
 		matchlen = longest_prefix_match(trie, node, key);
 
 		if (node->prefixlen != matchlen ||
@@ -442,8 +444,8 @@ static long trie_update_elem(struct bpf_map *map,
 	rcu_assign_pointer(*slot, im_node);
 
 out:
-	raw_spin_unlock_irqrestore(&trie->lock, irq_flags);
-
+	raw_res_spin_unlock_irqrestore(&trie->lock, irq_flags);
+out_free:
 	if (ret)
 		bpf_mem_cache_free(&trie->ma, new_node);
 	bpf_mem_cache_free_rcu(&trie->ma, free_node);
@@ -467,7 +469,9 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
 	if (key->prefixlen > trie->max_prefixlen)
 		return -EINVAL;
 
-	raw_spin_lock_irqsave(&trie->lock, irq_flags);
+	ret = raw_res_spin_lock_irqsave(&trie->lock, irq_flags);
+	if (ret)
+		return ret;
 
 	/* Walk the tree looking for an exact key/length match and keeping
 	 * track of the path we traverse.  We will need to know the node
@@ -478,8 +482,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
 	trim = &trie->root;
 	trim2 = trim;
 	parent = NULL;
-	while ((node = rcu_dereference_protected(
-		       *trim, lockdep_is_held(&trie->lock)))) {
+	while ((node = rcu_dereference(*trim))) {
 		matchlen = longest_prefix_match(trie, node, key);
 
 		if (node->prefixlen != matchlen ||
@@ -543,7 +546,7 @@ static long trie_delete_elem(struct bpf_map *map, void *_key)
 	free_node = node;
 
 out:
-	raw_spin_unlock_irqrestore(&trie->lock, irq_flags);
+	raw_res_spin_unlock_irqrestore(&trie->lock, irq_flags);
 
 	bpf_mem_cache_free_rcu(&trie->ma, free_parent);
 	bpf_mem_cache_free_rcu(&trie->ma, free_node);
@@ -592,7 +595,7 @@ static struct bpf_map *trie_alloc(union bpf_attr *attr)
 			  offsetof(struct bpf_lpm_trie_key_u8, data);
 	trie->max_prefixlen = trie->data_size * 8;
 
-	raw_spin_lock_init(&trie->lock);
+	raw_res_spin_lock_init(&trie->lock);
 
 	/* Allocate intermediate and leaf nodes from the same allocator */
 	leaf_size = sizeof(struct lpm_trie_node) + trie->data_size +
-- 
2.47.1

[PATCH bpf-next v4 22/25] bpf: Introduce rqspinlock kfuncs

[Kumar Kartikeya Dwivedi]

Introduce four new kfuncs, bpf_res_spin_lock, and bpf_res_spin_unlock,
and their irqsave/irqrestore variants, which wrap the rqspinlock APIs.
bpf_res_spin_lock returns a conditional result, depending on whether the
lock was acquired (NULL is returned when lock acquisition succeeds,
non-NULL upon failure). The memory pointed to by the returned pointer
upon failure can be dereferenced after the NULL check to obtain the
error code.

Instead of using the old bpf_spin_lock type, introduce a new type with
the same layout, and the same alignment, but a different name to avoid
type confusion.

Preemption is disabled upon successful lock acquisition, however IRQs
are not. Special kfuncs can be introduced later to allow disabling IRQs
when taking a spin lock. Resilient locks are safe against AA deadlocks,
hence not disabling IRQs currently does not allow violation of kernel
safety.

__irq_flag annotation is used to accept IRQ flags for the IRQ-variants,
with the same semantics as existing bpf_local_irq_{save, restore}.

These kfuncs will require additional verifier-side support in subsequent
commits, to allow programs to hold multiple locks at the same time.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/asm-generic/rqspinlock.h |  7 +++
 include/linux/bpf.h              |  1 +
 kernel/bpf/rqspinlock.c          | 78 ++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+)

diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index 23abd0b8d0f9..6d4244d643df 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -23,6 +23,13 @@ struct rqspinlock {
 	};
 };
 
+/* Even though this is same as struct rqspinlock, we need to emit a distinct
+ * type in BTF for BPF programs.
+ */
+struct bpf_res_spin_lock {
+	u32 val;
+};
+
 struct qspinlock;
 #ifdef CONFIG_QUEUED_SPINLOCKS
 typedef struct qspinlock rqspinlock_t;
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 0d7b70124d81..a6bc687d6300 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -30,6 +30,7 @@
 #include <linux/static_call.h>
 #include <linux/memcontrol.h>
 #include <linux/cfi.h>
+#include <asm/rqspinlock.h>
 
 struct bpf_verifier_env;
 struct bpf_verifier_log;
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index ad0fc35c647e..cf417a736559 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -15,6 +15,8 @@
 
 #include <linux/smp.h>
 #include <linux/bug.h>
+#include <linux/bpf.h>
+#include <linux/err.h>
 #include <linux/cpumask.h>
 #include <linux/percpu.h>
 #include <linux/hardirq.h>
@@ -690,3 +692,79 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
 EXPORT_SYMBOL_GPL(resilient_queued_spin_lock_slowpath);
 
 #endif /* CONFIG_QUEUED_SPINLOCKS */
+
+__bpf_kfunc_start_defs();
+
+#define REPORT_STR(ret) ({ ret == -ETIMEDOUT ? "Timeout detected" : "AA or ABBA deadlock detected"; })
+
+__bpf_kfunc int bpf_res_spin_lock(struct bpf_res_spin_lock *lock)
+{
+	int ret;
+
+	BUILD_BUG_ON(sizeof(rqspinlock_t) != sizeof(struct bpf_res_spin_lock));
+	BUILD_BUG_ON(__alignof__(rqspinlock_t) != __alignof__(struct bpf_res_spin_lock));
+
+	preempt_disable();
+	ret = res_spin_lock((rqspinlock_t *)lock);
+	if (unlikely(ret)) {
+		preempt_enable();
+		rqspinlock_report_violation(REPORT_STR(ret), lock);
+		return ret;
+	}
+	return 0;
+}
+
+__bpf_kfunc void bpf_res_spin_unlock(struct bpf_res_spin_lock *lock)
+{
+	res_spin_unlock((rqspinlock_t *)lock);
+	preempt_enable();
+}
+
+__bpf_kfunc int bpf_res_spin_lock_irqsave(struct bpf_res_spin_lock *lock, unsigned long *flags__irq_flag)
+{
+	u64 *ptr = (u64 *)flags__irq_flag;
+	unsigned long flags;
+	int ret;
+
+	preempt_disable();
+	local_irq_save(flags);
+	ret = res_spin_lock((rqspinlock_t *)lock);
+	if (unlikely(ret)) {
+		local_irq_restore(flags);
+		preempt_enable();
+		rqspinlock_report_violation(REPORT_STR(ret), lock);
+		return ret;
+	}
+	*ptr = flags;
+	return 0;
+}
+
+__bpf_kfunc void bpf_res_spin_unlock_irqrestore(struct bpf_res_spin_lock *lock, unsigned long *flags__irq_flag)
+{
+	u64 *ptr = (u64 *)flags__irq_flag;
+	unsigned long flags = *ptr;
+
+	res_spin_unlock((rqspinlock_t *)lock);
+	local_irq_restore(flags);
+	preempt_enable();
+}
+
+__bpf_kfunc_end_defs();
+
+BTF_KFUNCS_START(rqspinlock_kfunc_ids)
+BTF_ID_FLAGS(func, bpf_res_spin_lock, KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_res_spin_unlock)
+BTF_ID_FLAGS(func, bpf_res_spin_lock_irqsave, KF_RET_NULL)
+BTF_ID_FLAGS(func, bpf_res_spin_unlock_irqrestore)
+BTF_KFUNCS_END(rqspinlock_kfunc_ids)
+
+static const struct btf_kfunc_id_set rqspinlock_kfunc_set = {
+	.owner = THIS_MODULE,
+	.set = &rqspinlock_kfunc_ids,
+};
+
+static __init int rqspinlock_register_kfuncs(void)
+{
+	return register_btf_kfunc_id_set(BPF_PROG_TYPE_UNSPEC, &rqspinlock_kfunc_set);
+}
+late_initcall(rqspinlock_register_kfuncs);
-- 
2.47.1

[PATCH bpf-next v4 23/25] bpf: Implement verifier support for rqspinlock

[Kumar Kartikeya Dwivedi]

Introduce verifier-side support for rqspinlock kfuncs. The first step is
allowing bpf_res_spin_lock type to be defined in map values and
allocated objects, so BTF-side is updated with a new BPF_RES_SPIN_LOCK
field to recognize and validate.

Any object cannot have both bpf_spin_lock and bpf_res_spin_lock, only
one of them (and at most one of them per-object, like before) must be
present. The bpf_res_spin_lock can also be used to protect objects that
require lock protection for their kfuncs, like BPF rbtree and linked
list.

The verifier plumbing to simulate success and failure cases when calling
the kfuncs is done by pushing a new verifier state to the verifier state
stack which will verify the failure case upon calling the kfunc. The
path where success is indicated creates all lock reference state and IRQ
state (if necessary for irqsave variants). In the case of failure, the
state clears the registers r0-r5, sets the return value, and skips kfunc
processing, proceeding to the next instruction.

When marking the return value for success case, the value is marked as
0, and for the failure case as [-MAX_ERRNO, -1]. Then, in the program,
whenever user checks the return value as 'if (ret)' or 'if (ret < 0)'
the verifier never traverses such branches for success cases, and would
be aware that the lock is not held in such cases.

We push the kfunc state in check_kfunc_call whenever rqspinlock kfuncs
are invoked. We introduce a kfunc_class state to avoid mixing lock
irqrestore kfuncs with IRQ state created by bpf_local_irq_save.

With all this infrastructure, these kfuncs become usable in programs
while satisfying all safety properties required by the kernel.

Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf.h          |   9 ++
 include/linux/bpf_verifier.h |  16 ++-
 kernel/bpf/btf.c             |  26 ++++-
 kernel/bpf/syscall.c         |   6 +-
 kernel/bpf/verifier.c        | 219 ++++++++++++++++++++++++++++-------
 5 files changed, 231 insertions(+), 45 deletions(-)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index a6bc687d6300..c59384f62da0 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -205,6 +205,7 @@ enum btf_field_type {
 	BPF_REFCOUNT   = (1 << 9),
 	BPF_WORKQUEUE  = (1 << 10),
 	BPF_UPTR       = (1 << 11),
+	BPF_RES_SPIN_LOCK = (1 << 12),
 };
 
 typedef void (*btf_dtor_kfunc_t)(void *);
@@ -240,6 +241,7 @@ struct btf_record {
 	u32 cnt;
 	u32 field_mask;
 	int spin_lock_off;
+	int res_spin_lock_off;
 	int timer_off;
 	int wq_off;
 	int refcount_off;
@@ -315,6 +317,8 @@ static inline const char *btf_field_type_name(enum btf_field_type type)
 	switch (type) {
 	case BPF_SPIN_LOCK:
 		return "bpf_spin_lock";
+	case BPF_RES_SPIN_LOCK:
+		return "bpf_res_spin_lock";
 	case BPF_TIMER:
 		return "bpf_timer";
 	case BPF_WORKQUEUE:
@@ -347,6 +351,8 @@ static inline u32 btf_field_type_size(enum btf_field_type type)
 	switch (type) {
 	case BPF_SPIN_LOCK:
 		return sizeof(struct bpf_spin_lock);
+	case BPF_RES_SPIN_LOCK:
+		return sizeof(struct bpf_res_spin_lock);
 	case BPF_TIMER:
 		return sizeof(struct bpf_timer);
 	case BPF_WORKQUEUE:
@@ -377,6 +383,8 @@ static inline u32 btf_field_type_align(enum btf_field_type type)
 	switch (type) {
 	case BPF_SPIN_LOCK:
 		return __alignof__(struct bpf_spin_lock);
+	case BPF_RES_SPIN_LOCK:
+		return __alignof__(struct bpf_res_spin_lock);
 	case BPF_TIMER:
 		return __alignof__(struct bpf_timer);
 	case BPF_WORKQUEUE:
@@ -420,6 +428,7 @@ static inline void bpf_obj_init_field(const struct btf_field *field, void *addr)
 	case BPF_RB_ROOT:
 		/* RB_ROOT_CACHED 0-inits, no need to do anything after memset */
 	case BPF_SPIN_LOCK:
+	case BPF_RES_SPIN_LOCK:
 	case BPF_TIMER:
 	case BPF_WORKQUEUE:
 	case BPF_KPTR_UNREF:
diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index d6cfc4ee6820..bc073a48aed9 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -115,6 +115,14 @@ struct bpf_reg_state {
 			int depth:30;
 		} iter;
 
+		/* For irq stack slots */
+		struct {
+			enum {
+				IRQ_NATIVE_KFUNC,
+				IRQ_LOCK_KFUNC,
+			} kfunc_class;
+		} irq;
+
 		/* Max size from any of the above. */
 		struct {
 			unsigned long raw1;
@@ -255,9 +263,11 @@ struct bpf_reference_state {
 	 * default to pointer reference on zero initialization of a state.
 	 */
 	enum ref_state_type {
-		REF_TYPE_PTR	= 1,
-		REF_TYPE_IRQ	= 2,
-		REF_TYPE_LOCK	= 3,
+		REF_TYPE_PTR		= (1 << 1),
+		REF_TYPE_IRQ		= (1 << 2),
+		REF_TYPE_LOCK		= (1 << 3),
+		REF_TYPE_RES_LOCK 	= (1 << 4),
+		REF_TYPE_RES_LOCK_IRQ	= (1 << 5),
 	} type;
 	/* Track each reference created with a unique id, even if the same
 	 * instruction creates the reference multiple times (eg, via CALL).
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 519e3f5e9c10..f7a2bfb0c11a 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3481,6 +3481,15 @@ static int btf_get_field_type(const struct btf *btf, const struct btf_type *var_
 			goto end;
 		}
 	}
+	if (field_mask & BPF_RES_SPIN_LOCK) {
+		if (!strcmp(name, "bpf_res_spin_lock")) {
+			if (*seen_mask & BPF_RES_SPIN_LOCK)
+				return -E2BIG;
+			*seen_mask |= BPF_RES_SPIN_LOCK;
+			type = BPF_RES_SPIN_LOCK;
+			goto end;
+		}
+	}
 	if (field_mask & BPF_TIMER) {
 		if (!strcmp(name, "bpf_timer")) {
 			if (*seen_mask & BPF_TIMER)
@@ -3659,6 +3668,7 @@ static int btf_find_field_one(const struct btf *btf,
 
 	switch (field_type) {
 	case BPF_SPIN_LOCK:
+	case BPF_RES_SPIN_LOCK:
 	case BPF_TIMER:
 	case BPF_WORKQUEUE:
 	case BPF_LIST_NODE:
@@ -3952,6 +3962,7 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type
 		return ERR_PTR(-ENOMEM);
 
 	rec->spin_lock_off = -EINVAL;
+	rec->res_spin_lock_off = -EINVAL;
 	rec->timer_off = -EINVAL;
 	rec->wq_off = -EINVAL;
 	rec->refcount_off = -EINVAL;
@@ -3979,6 +3990,11 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type
 			/* Cache offset for faster lookup at runtime */
 			rec->spin_lock_off = rec->fields[i].offset;
 			break;
+		case BPF_RES_SPIN_LOCK:
+			WARN_ON_ONCE(rec->spin_lock_off >= 0);
+			/* Cache offset for faster lookup at runtime */
+			rec->res_spin_lock_off = rec->fields[i].offset;
+			break;
 		case BPF_TIMER:
 			WARN_ON_ONCE(rec->timer_off >= 0);
 			/* Cache offset for faster lookup at runtime */
@@ -4022,9 +4038,15 @@ struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type
 		rec->cnt++;
 	}
 
+	if (rec->spin_lock_off >= 0 && rec->res_spin_lock_off >= 0) {
+		ret = -EINVAL;
+		goto end;
+	}
+
 	/* bpf_{list_head, rb_node} require bpf_spin_lock */
 	if ((btf_record_has_field(rec, BPF_LIST_HEAD) ||
-	     btf_record_has_field(rec, BPF_RB_ROOT)) && rec->spin_lock_off < 0) {
+	     btf_record_has_field(rec, BPF_RB_ROOT)) &&
+		 (rec->spin_lock_off < 0 && rec->res_spin_lock_off < 0)) {
 		ret = -EINVAL;
 		goto end;
 	}
@@ -5637,7 +5659,7 @@ btf_parse_struct_metas(struct bpf_verifier_log *log, struct btf *btf)
 
 		type = &tab->types[tab->cnt];
 		type->btf_id = i;
-		record = btf_parse_fields(btf, t, BPF_SPIN_LOCK | BPF_LIST_HEAD | BPF_LIST_NODE |
+		record = btf_parse_fields(btf, t, BPF_SPIN_LOCK | BPF_RES_SPIN_LOCK | BPF_LIST_HEAD | BPF_LIST_NODE |
 						  BPF_RB_ROOT | BPF_RB_NODE | BPF_REFCOUNT |
 						  BPF_KPTR, t->size);
 		/* The record cannot be unset, treat it as an error if so */
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6a8f20ee2851..dba2628fe9a5 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -648,6 +648,7 @@ void btf_record_free(struct btf_record *rec)
 		case BPF_RB_ROOT:
 		case BPF_RB_NODE:
 		case BPF_SPIN_LOCK:
+		case BPF_RES_SPIN_LOCK:
 		case BPF_TIMER:
 		case BPF_REFCOUNT:
 		case BPF_WORKQUEUE:
@@ -700,6 +701,7 @@ struct btf_record *btf_record_dup(const struct btf_record *rec)
 		case BPF_RB_ROOT:
 		case BPF_RB_NODE:
 		case BPF_SPIN_LOCK:
+		case BPF_RES_SPIN_LOCK:
 		case BPF_TIMER:
 		case BPF_REFCOUNT:
 		case BPF_WORKQUEUE:
@@ -777,6 +779,7 @@ void bpf_obj_free_fields(const struct btf_record *rec, void *obj)
 
 		switch (fields[i].type) {
 		case BPF_SPIN_LOCK:
+		case BPF_RES_SPIN_LOCK:
 			break;
 		case BPF_TIMER:
 			bpf_timer_cancel_and_free(field_ptr);
@@ -1212,7 +1215,7 @@ static int map_check_btf(struct bpf_map *map, struct bpf_token *token,
 		return -EINVAL;
 
 	map->record = btf_parse_fields(btf, value_type,
-				       BPF_SPIN_LOCK | BPF_TIMER | BPF_KPTR | BPF_LIST_HEAD |
+				       BPF_SPIN_LOCK | BPF_RES_SPIN_LOCK | BPF_TIMER | BPF_KPTR | BPF_LIST_HEAD |
 				       BPF_RB_ROOT | BPF_REFCOUNT | BPF_WORKQUEUE | BPF_UPTR,
 				       map->value_size);
 	if (!IS_ERR_OR_NULL(map->record)) {
@@ -1231,6 +1234,7 @@ static int map_check_btf(struct bpf_map *map, struct bpf_token *token,
 			case 0:
 				continue;
 			case BPF_SPIN_LOCK:
+			case BPF_RES_SPIN_LOCK:
 				if (map->map_type != BPF_MAP_TYPE_HASH &&
 				    map->map_type != BPF_MAP_TYPE_ARRAY &&
 				    map->map_type != BPF_MAP_TYPE_CGROUP_STORAGE &&
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 3303a3605ee8..29121ad32a89 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -456,7 +456,7 @@ static bool subprog_is_exc_cb(struct bpf_verifier_env *env, int subprog)
 
 static bool reg_may_point_to_spin_lock(const struct bpf_reg_state *reg)
 {
-	return btf_record_has_field(reg_btf_record(reg), BPF_SPIN_LOCK);
+	return btf_record_has_field(reg_btf_record(reg), BPF_SPIN_LOCK | BPF_RES_SPIN_LOCK);
 }
 
 static bool type_is_rdonly_mem(u32 type)
@@ -1155,7 +1155,8 @@ static int release_irq_state(struct bpf_verifier_state *state, int id);
 
 static int mark_stack_slot_irq_flag(struct bpf_verifier_env *env,
 				     struct bpf_kfunc_call_arg_meta *meta,
-				     struct bpf_reg_state *reg, int insn_idx)
+				     struct bpf_reg_state *reg, int insn_idx,
+				     int kfunc_class)
 {
 	struct bpf_func_state *state = func(env, reg);
 	struct bpf_stack_state *slot;
@@ -1177,6 +1178,7 @@ static int mark_stack_slot_irq_flag(struct bpf_verifier_env *env,
 	st->type = PTR_TO_STACK; /* we don't have dedicated reg type */
 	st->live |= REG_LIVE_WRITTEN;
 	st->ref_obj_id = id;
+	st->irq.kfunc_class = kfunc_class;
 
 	for (i = 0; i < BPF_REG_SIZE; i++)
 		slot->slot_type[i] = STACK_IRQ_FLAG;
@@ -1185,7 +1187,8 @@ static int mark_stack_slot_irq_flag(struct bpf_verifier_env *env,
 	return 0;
 }
 
-static int unmark_stack_slot_irq_flag(struct bpf_verifier_env *env, struct bpf_reg_state *reg)
+static int unmark_stack_slot_irq_flag(struct bpf_verifier_env *env, struct bpf_reg_state *reg,
+				      int kfunc_class)
 {
 	struct bpf_func_state *state = func(env, reg);
 	struct bpf_stack_state *slot;
@@ -1199,6 +1202,15 @@ static int unmark_stack_slot_irq_flag(struct bpf_verifier_env *env, struct bpf_r
 	slot = &state->stack[spi];
 	st = &slot->spilled_ptr;
 
+	if (st->irq.kfunc_class != kfunc_class) {
+		const char *flag_kfunc = st->irq.kfunc_class == IRQ_NATIVE_KFUNC ? "native" : "lock";
+		const char *used_kfunc = kfunc_class == IRQ_NATIVE_KFUNC ? "native" : "lock";
+
+		verbose(env, "irq flag acquired by %s kfuncs cannot be restored with %s kfuncs\n",
+			flag_kfunc, used_kfunc);
+		return -EINVAL;
+	}
+
 	err = release_irq_state(env->cur_state, st->ref_obj_id);
 	WARN_ON_ONCE(err && err != -EACCES);
 	if (err) {
@@ -1609,7 +1621,7 @@ static struct bpf_reference_state *find_lock_state(struct bpf_verifier_state *st
 	for (i = 0; i < state->acquired_refs; i++) {
 		struct bpf_reference_state *s = &state->refs[i];
 
-		if (s->type != type)
+		if (!(s->type & type))
 			continue;
 
 		if (s->id == id && s->ptr == ptr)
@@ -8204,6 +8216,12 @@ static int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg
 	return err;
 }
 
+enum {
+	PROCESS_SPIN_LOCK = (1 << 0),
+	PROCESS_RES_LOCK  = (1 << 1),
+	PROCESS_LOCK_IRQ  = (1 << 2),
+};
+
 /* Implementation details:
  * bpf_map_lookup returns PTR_TO_MAP_VALUE_OR_NULL.
  * bpf_obj_new returns PTR_TO_BTF_ID | MEM_ALLOC | PTR_MAYBE_NULL.
@@ -8226,30 +8244,33 @@ static int check_kfunc_mem_size_reg(struct bpf_verifier_env *env, struct bpf_reg
  * env->cur_state->active_locks remembers which map value element or allocated
  * object got locked and clears it after bpf_spin_unlock.
  */
-static int process_spin_lock(struct bpf_verifier_env *env, int regno,
-			     bool is_lock)
+static int process_spin_lock(struct bpf_verifier_env *env, int regno, int flags)
 {
+	bool is_lock = flags & PROCESS_SPIN_LOCK, is_res_lock = flags & PROCESS_RES_LOCK;
+	const char *lock_str = is_res_lock ? "bpf_res_spin" : "bpf_spin";
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
 	struct bpf_verifier_state *cur = env->cur_state;
 	bool is_const = tnum_is_const(reg->var_off);
+	bool is_irq = flags & PROCESS_LOCK_IRQ;
 	u64 val = reg->var_off.value;
 	struct bpf_map *map = NULL;
 	struct btf *btf = NULL;
 	struct btf_record *rec;
+	u32 spin_lock_off;
 	int err;
 
 	if (!is_const) {
 		verbose(env,
-			"R%d doesn't have constant offset. bpf_spin_lock has to be at the constant offset\n",
-			regno);
+			"R%d doesn't have constant offset. %s_lock has to be at the constant offset\n",
+			regno, lock_str);
 		return -EINVAL;
 	}
 	if (reg->type == PTR_TO_MAP_VALUE) {
 		map = reg->map_ptr;
 		if (!map->btf) {
 			verbose(env,
-				"map '%s' has to have BTF in order to use bpf_spin_lock\n",
-				map->name);
+				"map '%s' has to have BTF in order to use %s_lock\n",
+				map->name, lock_str);
 			return -EINVAL;
 		}
 	} else {
@@ -8257,36 +8278,53 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 	}
 
 	rec = reg_btf_record(reg);
-	if (!btf_record_has_field(rec, BPF_SPIN_LOCK)) {
-		verbose(env, "%s '%s' has no valid bpf_spin_lock\n", map ? "map" : "local",
-			map ? map->name : "kptr");
+	if (!btf_record_has_field(rec, is_res_lock ? BPF_RES_SPIN_LOCK : BPF_SPIN_LOCK)) {
+		verbose(env, "%s '%s' has no valid %s_lock\n", map ? "map" : "local",
+			map ? map->name : "kptr", lock_str);
 		return -EINVAL;
 	}
-	if (rec->spin_lock_off != val + reg->off) {
-		verbose(env, "off %lld doesn't point to 'struct bpf_spin_lock' that is at %d\n",
-			val + reg->off, rec->spin_lock_off);
+	spin_lock_off = is_res_lock ? rec->res_spin_lock_off : rec->spin_lock_off;
+	if (spin_lock_off != val + reg->off) {
+		verbose(env, "off %lld doesn't point to 'struct %s_lock' that is at %d\n",
+			val + reg->off, lock_str, spin_lock_off);
 		return -EINVAL;
 	}
 	if (is_lock) {
 		void *ptr;
+		int type;
 
 		if (map)
 			ptr = map;
 		else
 			ptr = btf;
 
-		if (cur->active_locks) {
-			verbose(env,
-				"Locking two bpf_spin_locks are not allowed\n");
-			return -EINVAL;
+		if (!is_res_lock && cur->active_locks) {
+			if (find_lock_state(env->cur_state, REF_TYPE_LOCK, 0, NULL)) {
+				verbose(env,
+					"Locking two bpf_spin_locks are not allowed\n");
+				return -EINVAL;
+			}
+		} else if (is_res_lock && cur->active_locks) {
+			if (find_lock_state(env->cur_state, REF_TYPE_RES_LOCK | REF_TYPE_RES_LOCK_IRQ, reg->id, ptr)) {
+				verbose(env, "Acquiring the same lock again, AA deadlock detected\n");
+				return -EINVAL;
+			}
 		}
-		err = acquire_lock_state(env, env->insn_idx, REF_TYPE_LOCK, reg->id, ptr);
+
+		if (is_res_lock && is_irq)
+			type = REF_TYPE_RES_LOCK_IRQ;
+		else if (is_res_lock)
+			type = REF_TYPE_RES_LOCK;
+		else
+			type = REF_TYPE_LOCK;
+		err = acquire_lock_state(env, env->insn_idx, type, reg->id, ptr);
 		if (err < 0) {
 			verbose(env, "Failed to acquire lock state\n");
 			return err;
 		}
 	} else {
 		void *ptr;
+		int type;
 
 		if (map)
 			ptr = map;
@@ -8294,12 +8332,18 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno,
 			ptr = btf;
 
 		if (!cur->active_locks) {
-			verbose(env, "bpf_spin_unlock without taking a lock\n");
+			verbose(env, "%s_unlock without taking a lock\n", lock_str);
 			return -EINVAL;
 		}
 
-		if (release_lock_state(env->cur_state, REF_TYPE_LOCK, reg->id, ptr)) {
-			verbose(env, "bpf_spin_unlock of different lock\n");
+		if (is_res_lock && is_irq)
+			type = REF_TYPE_RES_LOCK_IRQ;
+		else if (is_res_lock)
+			type = REF_TYPE_RES_LOCK;
+		else
+			type = REF_TYPE_LOCK;
+		if (release_lock_state(cur, type, reg->id, ptr)) {
+			verbose(env, "%s_unlock of different lock\n", lock_str);
 			return -EINVAL;
 		}
 
@@ -9625,11 +9669,11 @@ static int check_func_arg(struct bpf_verifier_env *env, u32 arg,
 			return -EACCES;
 		}
 		if (meta->func_id == BPF_FUNC_spin_lock) {
-			err = process_spin_lock(env, regno, true);
+			err = process_spin_lock(env, regno, PROCESS_SPIN_LOCK);
 			if (err)
 				return err;
 		} else if (meta->func_id == BPF_FUNC_spin_unlock) {
-			err = process_spin_lock(env, regno, false);
+			err = process_spin_lock(env, regno, 0);
 			if (err)
 				return err;
 		} else {
@@ -11511,7 +11555,7 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 		regs[BPF_REG_0].map_uid = meta.map_uid;
 		regs[BPF_REG_0].type = PTR_TO_MAP_VALUE | ret_flag;
 		if (!type_may_be_null(ret_flag) &&
-		    btf_record_has_field(meta.map_ptr->record, BPF_SPIN_LOCK)) {
+		    btf_record_has_field(meta.map_ptr->record, BPF_SPIN_LOCK | BPF_RES_SPIN_LOCK)) {
 			regs[BPF_REG_0].id = ++env->id_gen;
 		}
 		break;
@@ -11683,10 +11727,10 @@ static int check_helper_call(struct bpf_verifier_env *env, struct bpf_insn *insn
 /* mark_btf_func_reg_size() is used when the reg size is determined by
  * the BTF func_proto's return value size and argument.
  */
-static void mark_btf_func_reg_size(struct bpf_verifier_env *env, u32 regno,
-				   size_t reg_size)
+static void __mark_btf_func_reg_size(struct bpf_verifier_env *env, struct bpf_reg_state *regs,
+				     u32 regno, size_t reg_size)
 {
-	struct bpf_reg_state *reg = &cur_regs(env)[regno];
+	struct bpf_reg_state *reg = &regs[regno];
 
 	if (regno == BPF_REG_0) {
 		/* Function return value */
@@ -11704,6 +11748,12 @@ static void mark_btf_func_reg_size(struct bpf_verifier_env *env, u32 regno,
 	}
 }
 
+static void mark_btf_func_reg_size(struct bpf_verifier_env *env, u32 regno,
+				   size_t reg_size)
+{
+	return __mark_btf_func_reg_size(env, cur_regs(env), regno, reg_size);
+}
+
 static bool is_kfunc_acquire(struct bpf_kfunc_call_arg_meta *meta)
 {
 	return meta->kfunc_flags & KF_ACQUIRE;
@@ -11841,6 +11891,7 @@ enum {
 	KF_ARG_RB_ROOT_ID,
 	KF_ARG_RB_NODE_ID,
 	KF_ARG_WORKQUEUE_ID,
+	KF_ARG_RES_SPIN_LOCK_ID,
 };
 
 BTF_ID_LIST(kf_arg_btf_ids)
@@ -11850,6 +11901,7 @@ BTF_ID(struct, bpf_list_node)
 BTF_ID(struct, bpf_rb_root)
 BTF_ID(struct, bpf_rb_node)
 BTF_ID(struct, bpf_wq)
+BTF_ID(struct, bpf_res_spin_lock)
 
 static bool __is_kfunc_ptr_arg_type(const struct btf *btf,
 				    const struct btf_param *arg, int type)
@@ -11898,6 +11950,11 @@ static bool is_kfunc_arg_wq(const struct btf *btf, const struct btf_param *arg)
 	return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_WORKQUEUE_ID);
 }
 
+static bool is_kfunc_arg_res_spin_lock(const struct btf *btf, const struct btf_param *arg)
+{
+	return __is_kfunc_ptr_arg_type(btf, arg, KF_ARG_RES_SPIN_LOCK_ID);
+}
+
 static bool is_kfunc_arg_callback(struct bpf_verifier_env *env, const struct btf *btf,
 				  const struct btf_param *arg)
 {
@@ -11969,6 +12026,7 @@ enum kfunc_ptr_arg_type {
 	KF_ARG_PTR_TO_MAP,
 	KF_ARG_PTR_TO_WORKQUEUE,
 	KF_ARG_PTR_TO_IRQ_FLAG,
+	KF_ARG_PTR_TO_RES_SPIN_LOCK,
 };
 
 enum special_kfunc_type {
@@ -12007,6 +12065,10 @@ enum special_kfunc_type {
 	KF_bpf_iter_num_destroy,
 	KF_bpf_set_dentry_xattr,
 	KF_bpf_remove_dentry_xattr,
+	KF_bpf_res_spin_lock,
+	KF_bpf_res_spin_unlock,
+	KF_bpf_res_spin_lock_irqsave,
+	KF_bpf_res_spin_unlock_irqrestore,
 };
 
 BTF_SET_START(special_kfunc_set)
@@ -12096,6 +12158,10 @@ BTF_ID(func, bpf_remove_dentry_xattr)
 BTF_ID_UNUSED
 BTF_ID_UNUSED
 #endif
+BTF_ID(func, bpf_res_spin_lock)
+BTF_ID(func, bpf_res_spin_unlock)
+BTF_ID(func, bpf_res_spin_lock_irqsave)
+BTF_ID(func, bpf_res_spin_unlock_irqrestore)
 
 static bool is_kfunc_ret_null(struct bpf_kfunc_call_arg_meta *meta)
 {
@@ -12189,6 +12255,9 @@ get_kfunc_ptr_arg_type(struct bpf_verifier_env *env,
 	if (is_kfunc_arg_irq_flag(meta->btf, &args[argno]))
 		return KF_ARG_PTR_TO_IRQ_FLAG;
 
+	if (is_kfunc_arg_res_spin_lock(meta->btf, &args[argno]))
+		return KF_ARG_PTR_TO_RES_SPIN_LOCK;
+
 	if ((base_type(reg->type) == PTR_TO_BTF_ID || reg2btf_ids[base_type(reg->type)])) {
 		if (!btf_type_is_struct(ref_t)) {
 			verbose(env, "kernel function %s args#%d pointer type %s %s is not supported\n",
@@ -12296,13 +12365,19 @@ static int process_irq_flag(struct bpf_verifier_env *env, int regno,
 			     struct bpf_kfunc_call_arg_meta *meta)
 {
 	struct bpf_reg_state *regs = cur_regs(env), *reg = &regs[regno];
+	int err, kfunc_class = IRQ_NATIVE_KFUNC;
 	bool irq_save;
-	int err;
 
-	if (meta->func_id == special_kfunc_list[KF_bpf_local_irq_save]) {
+	if (meta->func_id == special_kfunc_list[KF_bpf_local_irq_save] ||
+	    meta->func_id == special_kfunc_list[KF_bpf_res_spin_lock_irqsave]) {
 		irq_save = true;
-	} else if (meta->func_id == special_kfunc_list[KF_bpf_local_irq_restore]) {
+		if (meta->func_id == special_kfunc_list[KF_bpf_res_spin_lock_irqsave])
+			kfunc_class = IRQ_LOCK_KFUNC;
+	} else if (meta->func_id == special_kfunc_list[KF_bpf_local_irq_restore] ||
+		   meta->func_id == special_kfunc_list[KF_bpf_res_spin_unlock_irqrestore]) {
 		irq_save = false;
+		if (meta->func_id == special_kfunc_list[KF_bpf_res_spin_unlock_irqrestore])
+			kfunc_class = IRQ_LOCK_KFUNC;
 	} else {
 		verbose(env, "verifier internal error: unknown irq flags kfunc\n");
 		return -EFAULT;
@@ -12318,7 +12393,7 @@ static int process_irq_flag(struct bpf_verifier_env *env, int regno,
 		if (err)
 			return err;
 
-		err = mark_stack_slot_irq_flag(env, meta, reg, env->insn_idx);
+		err = mark_stack_slot_irq_flag(env, meta, reg, env->insn_idx, kfunc_class);
 		if (err)
 			return err;
 	} else {
@@ -12332,7 +12407,7 @@ static int process_irq_flag(struct bpf_verifier_env *env, int regno,
 		if (err)
 			return err;
 
-		err = unmark_stack_slot_irq_flag(env, reg);
+		err = unmark_stack_slot_irq_flag(env, reg, kfunc_class);
 		if (err)
 			return err;
 	}
@@ -12459,7 +12534,8 @@ static int check_reg_allocation_locked(struct bpf_verifier_env *env, struct bpf_
 
 	if (!env->cur_state->active_locks)
 		return -EINVAL;
-	s = find_lock_state(env->cur_state, REF_TYPE_LOCK, id, ptr);
+	s = find_lock_state(env->cur_state, REF_TYPE_LOCK | REF_TYPE_RES_LOCK | REF_TYPE_RES_LOCK_IRQ,
+			    id, ptr);
 	if (!s) {
 		verbose(env, "held lock and object are not in the same allocation\n");
 		return -EINVAL;
@@ -12495,9 +12571,18 @@ static bool is_bpf_graph_api_kfunc(u32 btf_id)
 	       btf_id == special_kfunc_list[KF_bpf_refcount_acquire_impl];
 }
 
+static bool is_bpf_res_spin_lock_kfunc(u32 btf_id)
+{
+	return btf_id == special_kfunc_list[KF_bpf_res_spin_lock] ||
+	       btf_id == special_kfunc_list[KF_bpf_res_spin_unlock] ||
+	       btf_id == special_kfunc_list[KF_bpf_res_spin_lock_irqsave] ||
+	       btf_id == special_kfunc_list[KF_bpf_res_spin_unlock_irqrestore];
+}
+
 static bool kfunc_spin_allowed(u32 btf_id)
 {
-	return is_bpf_graph_api_kfunc(btf_id) || is_bpf_iter_num_api_kfunc(btf_id);
+	return is_bpf_graph_api_kfunc(btf_id) || is_bpf_iter_num_api_kfunc(btf_id) ||
+	       is_bpf_res_spin_lock_kfunc(btf_id);
 }
 
 static bool is_sync_callback_calling_kfunc(u32 btf_id)
@@ -12929,6 +13014,7 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 		case KF_ARG_PTR_TO_CONST_STR:
 		case KF_ARG_PTR_TO_WORKQUEUE:
 		case KF_ARG_PTR_TO_IRQ_FLAG:
+		case KF_ARG_PTR_TO_RES_SPIN_LOCK:
 			break;
 		default:
 			WARN_ON_ONCE(1);
@@ -13227,6 +13313,28 @@ static int check_kfunc_args(struct bpf_verifier_env *env, struct bpf_kfunc_call_
 			if (ret < 0)
 				return ret;
 			break;
+		case KF_ARG_PTR_TO_RES_SPIN_LOCK:
+		{
+			int flags = PROCESS_RES_LOCK;
+
+			if (reg->type != PTR_TO_MAP_VALUE && reg->type != (PTR_TO_BTF_ID | MEM_ALLOC)) {
+				verbose(env, "arg#%d doesn't point to map value or allocated object\n", i);
+				return -EINVAL;
+			}
+
+			if (!is_bpf_res_spin_lock_kfunc(meta->func_id))
+				return -EFAULT;
+			if (meta->func_id == special_kfunc_list[KF_bpf_res_spin_lock] ||
+			    meta->func_id == special_kfunc_list[KF_bpf_res_spin_lock_irqsave])
+				flags |= PROCESS_SPIN_LOCK;
+			if (meta->func_id == special_kfunc_list[KF_bpf_res_spin_lock_irqsave] ||
+			    meta->func_id == special_kfunc_list[KF_bpf_res_spin_unlock_irqrestore])
+				flags |= PROCESS_LOCK_IRQ;
+			ret = process_spin_lock(env, regno, flags);
+			if (ret < 0)
+				return ret;
+			break;
+		}
 		}
 	}
 
@@ -13312,6 +13420,33 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 
 	insn_aux->is_iter_next = is_iter_next_kfunc(&meta);
 
+	if (!insn->off &&
+	    (insn->imm == special_kfunc_list[KF_bpf_res_spin_lock] ||
+	     insn->imm == special_kfunc_list[KF_bpf_res_spin_lock_irqsave])) {
+		struct bpf_verifier_state *branch;
+		struct bpf_reg_state *regs;
+
+		branch = push_stack(env, env->insn_idx + 1, env->insn_idx, false);
+		if (!branch) {
+			verbose(env, "failed to push state for failed lock acquisition\n");
+			return -ENOMEM;
+		}
+
+		regs = branch->frame[branch->curframe]->regs;
+
+		/* Clear r0-r5 registers in forked state */
+		for (i = 0; i < CALLER_SAVED_REGS; i++)
+			mark_reg_not_init(env, regs, caller_saved[i]);
+
+		mark_reg_unknown(env, regs, BPF_REG_0);
+		err = __mark_reg_s32_range(env, regs, BPF_REG_0, -MAX_ERRNO, -1);
+		if (err) {
+			verbose(env, "failed to mark s32 range for retval in forked state for lock\n");
+			return err;
+		}
+		__mark_btf_func_reg_size(env, regs, BPF_REG_0, sizeof(u32));
+	}
+
 	if (is_kfunc_destructive(&meta) && !capable(CAP_SYS_BOOT)) {
 		verbose(env, "destructive kfunc calls require CAP_SYS_BOOT capability\n");
 		return -EACCES;
@@ -13482,6 +13617,9 @@ static int check_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
 
 	if (btf_type_is_scalar(t)) {
 		mark_reg_unknown(env, regs, BPF_REG_0);
+		if (meta.btf == btf_vmlinux && (meta.func_id == special_kfunc_list[KF_bpf_res_spin_lock] ||
+		    meta.func_id == special_kfunc_list[KF_bpf_res_spin_lock_irqsave]))
+			__mark_reg_const_zero(env, &regs[BPF_REG_0]);
 		mark_btf_func_reg_size(env, BPF_REG_0, t->size);
 	} else if (btf_type_is_ptr(t)) {
 		ptr_type = btf_type_skip_modifiers(desc_btf, t->type, &ptr_type_id);
@@ -18417,7 +18555,8 @@ static bool stacksafe(struct bpf_verifier_env *env, struct bpf_func_state *old,
 		case STACK_IRQ_FLAG:
 			old_reg = &old->stack[spi].spilled_ptr;
 			cur_reg = &cur->stack[spi].spilled_ptr;
-			if (!check_ids(old_reg->ref_obj_id, cur_reg->ref_obj_id, idmap))
+			if (!check_ids(old_reg->ref_obj_id, cur_reg->ref_obj_id, idmap) ||
+			    old_reg->irq.kfunc_class != cur_reg->irq.kfunc_class)
 				return false;
 			break;
 		case STACK_MISC:
@@ -18461,6 +18600,8 @@ static bool refsafe(struct bpf_verifier_state *old, struct bpf_verifier_state *c
 		case REF_TYPE_IRQ:
 			break;
 		case REF_TYPE_LOCK:
+		case REF_TYPE_RES_LOCK:
+		case REF_TYPE_RES_LOCK_IRQ:
 			if (old->refs[i].ptr != cur->refs[i].ptr)
 				return false;
 			break;
@@ -19746,7 +19887,7 @@ static int check_map_prog_compatibility(struct bpf_verifier_env *env,
 		}
 	}
 
-	if (btf_record_has_field(map->record, BPF_SPIN_LOCK)) {
+	if (btf_record_has_field(map->record, BPF_SPIN_LOCK | BPF_RES_SPIN_LOCK)) {
 		if (prog_type == BPF_PROG_TYPE_SOCKET_FILTER) {
 			verbose(env, "socket filter progs cannot use bpf_spin_lock yet\n");
 			return -EINVAL;
-- 
2.47.1

[PATCH bpf-next v4 24/25] bpf: Maintain FIFO property for rqspinlock unlock

[Kumar Kartikeya Dwivedi]

Since out-of-order unlocks are unsupported for rqspinlock, and irqsave
variants enforce strict FIFO ordering anyway, make the same change for
normal non-irqsave variants, such that FIFO ordering is enforced.

Two new verifier state fields (active_lock_id, active_lock_ptr) are used
to denote the top of the stack, and prev_id and prev_ptr are ascertained
whenever popping the topmost entry through an unlock.

Take special care to make these fields part of the state comparison in
refsafe.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 include/linux/bpf_verifier.h |  3 +++
 kernel/bpf/verifier.c        | 33 ++++++++++++++++++++++++++++-----
 2 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
index bc073a48aed9..9734544b6957 100644
--- a/include/linux/bpf_verifier.h
+++ b/include/linux/bpf_verifier.h
@@ -268,6 +268,7 @@ struct bpf_reference_state {
 		REF_TYPE_LOCK		= (1 << 3),
 		REF_TYPE_RES_LOCK 	= (1 << 4),
 		REF_TYPE_RES_LOCK_IRQ	= (1 << 5),
+		REF_TYPE_LOCK_MASK	= REF_TYPE_LOCK | REF_TYPE_RES_LOCK | REF_TYPE_RES_LOCK_IRQ,
 	} type;
 	/* Track each reference created with a unique id, even if the same
 	 * instruction creates the reference multiple times (eg, via CALL).
@@ -434,6 +435,8 @@ struct bpf_verifier_state {
 	u32 active_locks;
 	u32 active_preempt_locks;
 	u32 active_irq_id;
+	u32 active_lock_id;
+	void *active_lock_ptr;
 	bool active_rcu_lock;
 
 	bool speculative;
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 29121ad32a89..4057081e996f 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -1428,6 +1428,8 @@ static int copy_reference_state(struct bpf_verifier_state *dst, const struct bpf
 	dst->active_preempt_locks = src->active_preempt_locks;
 	dst->active_rcu_lock = src->active_rcu_lock;
 	dst->active_irq_id = src->active_irq_id;
+	dst->active_lock_id = src->active_lock_id;
+	dst->active_lock_ptr = src->active_lock_ptr;
 	return 0;
 }
 
@@ -1527,6 +1529,8 @@ static int acquire_lock_state(struct bpf_verifier_env *env, int insn_idx, enum r
 	s->ptr = ptr;
 
 	state->active_locks++;
+	state->active_lock_id = id;
+	state->active_lock_ptr = ptr;
 	return 0;
 }
 
@@ -1577,16 +1581,24 @@ static bool find_reference_state(struct bpf_verifier_state *state, int ptr_id)
 
 static int release_lock_state(struct bpf_verifier_state *state, int type, int id, void *ptr)
 {
+	void *prev_ptr = NULL;
+	u32 prev_id = 0;
 	int i;
 
 	for (i = 0; i < state->acquired_refs; i++) {
-		if (state->refs[i].type != type)
-			continue;
-		if (state->refs[i].id == id && state->refs[i].ptr == ptr) {
+		if (state->refs[i].type == type && state->refs[i].id == id &&
+		    state->refs[i].ptr == ptr) {
 			release_reference_state(state, i);
 			state->active_locks--;
+			/* Reassign active lock (id, ptr). */
+			state->active_lock_id = prev_id;
+			state->active_lock_ptr = prev_ptr;
 			return 0;
 		}
+		if (state->refs[i].type & REF_TYPE_LOCK_MASK) {
+			prev_id = state->refs[i].id;
+			prev_ptr = state->refs[i].ptr;
+		}
 	}
 	return -EINVAL;
 }
@@ -8342,6 +8354,14 @@ static int process_spin_lock(struct bpf_verifier_env *env, int regno, int flags)
 			type = REF_TYPE_RES_LOCK;
 		else
 			type = REF_TYPE_LOCK;
+		if (!find_lock_state(cur, type, reg->id, ptr)) {
+			verbose(env, "%s_unlock of different lock\n", lock_str);
+			return -EINVAL;
+		}
+		if (reg->id != cur->active_lock_id || ptr != cur->active_lock_ptr) {
+			verbose(env, "%s_unlock cannot be out of order\n", lock_str);
+			return -EINVAL;
+		}
 		if (release_lock_state(cur, type, reg->id, ptr)) {
 			verbose(env, "%s_unlock of different lock\n", lock_str);
 			return -EINVAL;
@@ -12534,8 +12554,7 @@ static int check_reg_allocation_locked(struct bpf_verifier_env *env, struct bpf_
 
 	if (!env->cur_state->active_locks)
 		return -EINVAL;
-	s = find_lock_state(env->cur_state, REF_TYPE_LOCK | REF_TYPE_RES_LOCK | REF_TYPE_RES_LOCK_IRQ,
-			    id, ptr);
+	s = find_lock_state(env->cur_state, REF_TYPE_LOCK_MASK, id, ptr);
 	if (!s) {
 		verbose(env, "held lock and object are not in the same allocation\n");
 		return -EINVAL;
@@ -18591,6 +18610,10 @@ static bool refsafe(struct bpf_verifier_state *old, struct bpf_verifier_state *c
 	if (!check_ids(old->active_irq_id, cur->active_irq_id, idmap))
 		return false;
 
+	if (!check_ids(old->active_lock_id, cur->active_lock_id, idmap) ||
+	    old->active_lock_ptr != cur->active_lock_ptr)
+		return false;
+
 	for (i = 0; i < old->acquired_refs; i++) {
 		if (!check_ids(old->refs[i].id, cur->refs[i].id, idmap) ||
 		    old->refs[i].type != cur->refs[i].type)
-- 
2.47.1

[PATCH bpf-next v4 25/25] selftests/bpf: Add tests for rqspinlock

[Kumar Kartikeya Dwivedi]

Introduce selftests that trigger AA, ABBA deadlocks, and test the edge
case where the held locks table runs out of entries, since we then
fallback to the timeout as the final line of defense. Also exercise
verifier's AA detection where applicable.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
---
 .../selftests/bpf/prog_tests/res_spin_lock.c  |  98 +++++++
 tools/testing/selftests/bpf/progs/irq.c       |  53 ++++
 .../selftests/bpf/progs/res_spin_lock.c       | 143 ++++++++++
 .../selftests/bpf/progs/res_spin_lock_fail.c  | 244 ++++++++++++++++++
 4 files changed, 538 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/prog_tests/res_spin_lock.c
 create mode 100644 tools/testing/selftests/bpf/progs/res_spin_lock.c
 create mode 100644 tools/testing/selftests/bpf/progs/res_spin_lock_fail.c

diff --git a/tools/testing/selftests/bpf/prog_tests/res_spin_lock.c b/tools/testing/selftests/bpf/prog_tests/res_spin_lock.c
new file mode 100644
index 000000000000..115287ba441b
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/res_spin_lock.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024-2025 Meta Platforms, Inc. and affiliates. */
+#include <test_progs.h>
+#include <network_helpers.h>
+#include <sys/sysinfo.h>
+
+#include "res_spin_lock.skel.h"
+#include "res_spin_lock_fail.skel.h"
+
+void test_res_spin_lock_failure(void)
+{
+	RUN_TESTS(res_spin_lock_fail);
+}
+
+static volatile int skip;
+
+static void *spin_lock_thread(void *arg)
+{
+	int err, prog_fd = *(u32 *) arg;
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = 10000,
+	);
+
+	while (!READ_ONCE(skip)) {
+		err = bpf_prog_test_run_opts(prog_fd, &topts);
+		ASSERT_OK(err, "test_run");
+		ASSERT_OK(topts.retval, "test_run retval");
+	}
+	pthread_exit(arg);
+}
+
+void test_res_spin_lock_success(void)
+{
+	LIBBPF_OPTS(bpf_test_run_opts, topts,
+		.data_in = &pkt_v4,
+		.data_size_in = sizeof(pkt_v4),
+		.repeat = 1,
+	);
+	struct res_spin_lock *skel;
+	pthread_t thread_id[16];
+	int prog_fd, i, err;
+	void *ret;
+
+	if (get_nprocs() < 2) {
+		test__skip();
+		return;
+	}
+
+	skel = res_spin_lock__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "res_spin_lock__open_and_load"))
+		return;
+	/* AA deadlock */
+	prog_fd = bpf_program__fd(skel->progs.res_spin_lock_test);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "error");
+	ASSERT_OK(topts.retval, "retval");
+
+	prog_fd = bpf_program__fd(skel->progs.res_spin_lock_test_held_lock_max);
+	err = bpf_prog_test_run_opts(prog_fd, &topts);
+	ASSERT_OK(err, "error");
+	ASSERT_OK(topts.retval, "retval");
+
+	/* Multi-threaded ABBA deadlock. */
+
+	prog_fd = bpf_program__fd(skel->progs.res_spin_lock_test_AB);
+	for (i = 0; i < 16; i++) {
+		int err;
+
+		err = pthread_create(&thread_id[i], NULL, &spin_lock_thread, &prog_fd);
+		if (!ASSERT_OK(err, "pthread_create"))
+			goto end;
+	}
+
+	topts.retval = 0;
+	topts.repeat = 1000;
+	int fd = bpf_program__fd(skel->progs.res_spin_lock_test_BA);
+	while (!topts.retval && !err && !READ_ONCE(skel->bss->err)) {
+		err = bpf_prog_test_run_opts(fd, &topts);
+	}
+
+	WRITE_ONCE(skip, true);
+
+	for (i = 0; i < 16; i++) {
+		if (!ASSERT_OK(pthread_join(thread_id[i], &ret), "pthread_join"))
+			goto end;
+		if (!ASSERT_EQ(ret, &prog_fd, "ret == prog_fd"))
+			goto end;
+	}
+
+	ASSERT_EQ(READ_ONCE(skel->bss->err), -EDEADLK, "timeout err");
+	ASSERT_OK(err, "err");
+	ASSERT_EQ(topts.retval, -EDEADLK, "timeout");
+end:
+	res_spin_lock__destroy(skel);
+	return;
+}
diff --git a/tools/testing/selftests/bpf/progs/irq.c b/tools/testing/selftests/bpf/progs/irq.c
index 298d48d7886d..74d912b22de9 100644
--- a/tools/testing/selftests/bpf/progs/irq.c
+++ b/tools/testing/selftests/bpf/progs/irq.c
@@ -11,6 +11,9 @@ extern void bpf_local_irq_save(unsigned long *) __weak __ksym;
 extern void bpf_local_irq_restore(unsigned long *) __weak __ksym;
 extern int bpf_copy_from_user_str(void *dst, u32 dst__sz, const void *unsafe_ptr__ign, u64 flags) __weak __ksym;
 
+struct bpf_res_spin_lock lockA __hidden SEC(".data.A");
+struct bpf_res_spin_lock lockB __hidden SEC(".data.B");
+
 SEC("?tc")
 __failure __msg("arg#0 doesn't point to an irq flag on stack")
 int irq_save_bad_arg(struct __sk_buff *ctx)
@@ -510,4 +513,54 @@ int irq_sleepable_global_subprog_indirect(void *ctx)
 	return 0;
 }
 
+SEC("?tc")
+__failure __msg("cannot restore irq state out of order")
+int irq_ooo_lock_cond_inv(struct __sk_buff *ctx)
+{
+	unsigned long flags1, flags2;
+
+	if (bpf_res_spin_lock_irqsave(&lockA, &flags1))
+		return 0;
+	if (bpf_res_spin_lock_irqsave(&lockB, &flags2)) {
+		bpf_res_spin_unlock_irqrestore(&lockA, &flags1);
+		return 0;
+	}
+
+	bpf_res_spin_unlock_irqrestore(&lockB, &flags1);
+	bpf_res_spin_unlock_irqrestore(&lockA, &flags2);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("function calls are not allowed")
+int irq_wrong_kfunc_class_1(struct __sk_buff *ctx)
+{
+	unsigned long flags1;
+
+	if (bpf_res_spin_lock_irqsave(&lockA, &flags1))
+		return 0;
+	/* For now, bpf_local_irq_restore is not allowed in critical section,
+	 * but this test ensures error will be caught with kfunc_class when it's
+	 * opened up. Tested by temporarily permitting this kfunc in critical
+	 * section.
+	 */
+	bpf_local_irq_restore(&flags1);
+	bpf_res_spin_unlock_irqrestore(&lockA, &flags1);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("function calls are not allowed")
+int irq_wrong_kfunc_class_2(struct __sk_buff *ctx)
+{
+	unsigned long flags1, flags2;
+
+	bpf_local_irq_save(&flags1);
+	if (bpf_res_spin_lock_irqsave(&lockA, &flags2))
+		return 0;
+	bpf_local_irq_restore(&flags2);
+	bpf_res_spin_unlock_irqrestore(&lockA, &flags1);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/res_spin_lock.c b/tools/testing/selftests/bpf/progs/res_spin_lock.c
new file mode 100644
index 000000000000..b33385dfbd35
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/res_spin_lock.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024-2025 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include "bpf_misc.h"
+
+#define EDEADLK 35
+#define ETIMEDOUT 110
+
+struct arr_elem {
+	struct bpf_res_spin_lock lock;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 64);
+	__type(key, int);
+	__type(value, struct arr_elem);
+} arrmap SEC(".maps");
+
+struct bpf_res_spin_lock lockA __hidden SEC(".data.A");
+struct bpf_res_spin_lock lockB __hidden SEC(".data.B");
+
+SEC("tc")
+int res_spin_lock_test(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem1, *elem2;
+	int r;
+
+	elem1 = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem1)
+		return -1;
+	elem2 = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem2)
+		return -1;
+
+	r = bpf_res_spin_lock(&elem1->lock);
+	if (r)
+		return r;
+	if (!bpf_res_spin_lock(&elem2->lock)) {
+		bpf_res_spin_unlock(&elem2->lock);
+		bpf_res_spin_unlock(&elem1->lock);
+		return -1;
+	}
+	bpf_res_spin_unlock(&elem1->lock);
+	return 0;
+}
+
+SEC("tc")
+int res_spin_lock_test_AB(struct __sk_buff *ctx)
+{
+	int r;
+
+	r = bpf_res_spin_lock(&lockA);
+	if (r)
+		return !r;
+	/* Only unlock if we took the lock. */
+	if (!bpf_res_spin_lock(&lockB))
+		bpf_res_spin_unlock(&lockB);
+	bpf_res_spin_unlock(&lockA);
+	return 0;
+}
+
+int err;
+
+SEC("tc")
+int res_spin_lock_test_BA(struct __sk_buff *ctx)
+{
+	int r;
+
+	r = bpf_res_spin_lock(&lockB);
+	if (r)
+		return !r;
+	if (!bpf_res_spin_lock(&lockA))
+		bpf_res_spin_unlock(&lockA);
+	else
+		err = -EDEADLK;
+	bpf_res_spin_unlock(&lockB);
+	return err ?: 0;
+}
+
+SEC("tc")
+int res_spin_lock_test_held_lock_max(struct __sk_buff *ctx)
+{
+	struct bpf_res_spin_lock *locks[48] = {};
+	struct arr_elem *e;
+	u64 time_beg, time;
+	int ret = 0, i;
+
+	_Static_assert(ARRAY_SIZE(((struct rqspinlock_held){}).locks) == 31,
+		       "RES_NR_HELD assumed to be 31");
+
+	for (i = 0; i < 34; i++) {
+		int key = i;
+
+		/* We cannot pass in i as it will get spilled/filled by the compiler and
+		 * loses bounds in verifier state.
+		 */
+		e = bpf_map_lookup_elem(&arrmap, &key);
+		if (!e)
+			return 1;
+		locks[i] = &e->lock;
+	}
+
+	for (; i < 48; i++) {
+		int key = i - 2;
+
+		/* We cannot pass in i as it will get spilled/filled by the compiler and
+		 * loses bounds in verifier state.
+		 */
+		e = bpf_map_lookup_elem(&arrmap, &key);
+		if (!e)
+			return 1;
+		locks[i] = &e->lock;
+	}
+
+	time_beg = bpf_ktime_get_ns();
+	for (i = 0; i < 34; i++) {
+		if (bpf_res_spin_lock(locks[i]))
+			goto end;
+	}
+
+	/* Trigger AA, after exhausting entries in the held lock table. This
+	 * time, only the timeout can save us, as AA detection won't succeed.
+	 */
+	if (!bpf_res_spin_lock(locks[34])) {
+		bpf_res_spin_unlock(locks[34]);
+		ret = 1;
+		goto end;
+	}
+
+end:
+	for (i = i - 1; i >= 0; i--)
+		bpf_res_spin_unlock(locks[i]);
+	time = bpf_ktime_get_ns() - time_beg;
+	/* Time spent should be easily above our limit (1/4 s), since AA
+	 * detection won't be expedited due to lack of held lock entry.
+	 */
+	return ret ?: (time > 1000000000 / 4 ? 0 : 1);
+}
+
+char _license[] SEC("license") = "GPL";
diff --git a/tools/testing/selftests/bpf/progs/res_spin_lock_fail.c b/tools/testing/selftests/bpf/progs/res_spin_lock_fail.c
new file mode 100644
index 000000000000..330682a88c16
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/res_spin_lock_fail.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2024-2025 Meta Platforms, Inc. and affiliates. */
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_core_read.h>
+#include "bpf_misc.h"
+#include "bpf_experimental.h"
+
+struct arr_elem {
+	struct bpf_res_spin_lock lock;
+};
+
+struct {
+	__uint(type, BPF_MAP_TYPE_ARRAY);
+	__uint(max_entries, 1);
+	__type(key, int);
+	__type(value, struct arr_elem);
+} arrmap SEC(".maps");
+
+long value;
+
+struct bpf_spin_lock lock __hidden SEC(".data.A");
+struct bpf_res_spin_lock res_lock __hidden SEC(".data.B");
+
+SEC("?tc")
+__failure __msg("point to map value or allocated object")
+int res_spin_lock_arg(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	bpf_res_spin_lock((struct bpf_res_spin_lock *)bpf_core_cast(&elem->lock, struct __sk_buff));
+	bpf_res_spin_lock(&elem->lock);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("AA deadlock detected")
+int res_spin_lock_AA(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	bpf_res_spin_lock(&elem->lock);
+	bpf_res_spin_lock(&elem->lock);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("AA deadlock detected")
+int res_spin_lock_cond_AA(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	if (bpf_res_spin_lock(&elem->lock))
+		return 0;
+	bpf_res_spin_lock(&elem->lock);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("unlock of different lock")
+int res_spin_lock_mismatch_1(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	if (bpf_res_spin_lock(&elem->lock))
+		return 0;
+	bpf_res_spin_unlock(&res_lock);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("unlock of different lock")
+int res_spin_lock_mismatch_2(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	if (bpf_res_spin_lock(&res_lock))
+		return 0;
+	bpf_res_spin_unlock(&elem->lock);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("unlock of different lock")
+int res_spin_lock_irq_mismatch_1(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+	unsigned long f1;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	bpf_local_irq_save(&f1);
+	if (bpf_res_spin_lock(&res_lock))
+		return 0;
+	bpf_res_spin_unlock_irqrestore(&res_lock, &f1);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("unlock of different lock")
+int res_spin_lock_irq_mismatch_2(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+	unsigned long f1;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	if (bpf_res_spin_lock_irqsave(&res_lock, &f1))
+		return 0;
+	bpf_res_spin_unlock(&res_lock);
+	return 0;
+}
+
+SEC("?tc")
+__success
+int res_spin_lock_ooo(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	if (bpf_res_spin_lock(&res_lock))
+		return 0;
+	if (bpf_res_spin_lock(&elem->lock)) {
+		bpf_res_spin_unlock(&res_lock);
+		return 0;
+	}
+	bpf_res_spin_unlock(&elem->lock);
+	bpf_res_spin_unlock(&res_lock);
+	return 0;
+}
+
+SEC("?tc")
+__success
+int res_spin_lock_ooo_irq(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+	unsigned long f1, f2;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	if (bpf_res_spin_lock_irqsave(&res_lock, &f1))
+		return 0;
+	if (bpf_res_spin_lock_irqsave(&elem->lock, &f2)) {
+		bpf_res_spin_unlock_irqrestore(&res_lock, &f1);
+		/* We won't have a unreleased IRQ flag error here. */
+		return 0;
+	}
+	bpf_res_spin_unlock_irqrestore(&elem->lock, &f2);
+	bpf_res_spin_unlock_irqrestore(&res_lock, &f1);
+	return 0;
+}
+
+struct bpf_res_spin_lock lock1 __hidden SEC(".data.OO1");
+struct bpf_res_spin_lock lock2 __hidden SEC(".data.OO2");
+
+SEC("?tc")
+__failure __msg("bpf_res_spin_unlock cannot be out of order")
+int res_spin_lock_ooo_unlock(struct __sk_buff *ctx)
+{
+	if (bpf_res_spin_lock(&lock1))
+		return 0;
+	if (bpf_res_spin_lock(&lock2)) {
+		bpf_res_spin_unlock(&lock1);
+		return 0;
+	}
+	bpf_res_spin_unlock(&lock1);
+	bpf_res_spin_unlock(&lock2);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("off 1 doesn't point to 'struct bpf_res_spin_lock' that is at 0")
+int res_spin_lock_bad_off(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem)
+		return 0;
+	bpf_res_spin_lock((void *)&elem->lock + 1);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("R1 doesn't have constant offset. bpf_res_spin_lock has to be at the constant offset")
+int res_spin_lock_var_off(struct __sk_buff *ctx)
+{
+	struct arr_elem *elem;
+	u64 val = value;
+
+	elem = bpf_map_lookup_elem(&arrmap, &(int){0});
+	if (!elem) {
+		// FIXME: Only inline assembly use in assert macro doesn't emit
+		//	  BTF definition.
+		bpf_throw(0);
+		return 0;
+	}
+	bpf_assert_range(val, 0, 40);
+	bpf_res_spin_lock((void *)&value + val);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("map 'res_spin.bss' has no valid bpf_res_spin_lock")
+int res_spin_lock_no_lock_map(struct __sk_buff *ctx)
+{
+	bpf_res_spin_lock((void *)&value + 1);
+	return 0;
+}
+
+SEC("?tc")
+__failure __msg("local 'kptr' has no valid bpf_res_spin_lock")
+int res_spin_lock_no_lock_kptr(struct __sk_buff *ctx)
+{
+	struct { int i; } *p = bpf_obj_new(typeof(*p));
+
+	if (!p)
+		return 0;
+	bpf_res_spin_lock((void *)p);
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.47.1

Re: [PATCH bpf-next v4 00/25] Resilient Queued Spin Lock

[Alexei Starovoitov]

On Sat, Mar 15, 2025 at 9:05 PM Kumar Kartikeya Dwivedi
<memxor@gmail.com> wrote:
>
> Changelog:
> ----------
> v3 -> v4
> v4: https://lore.kernel.org/bpf/20250303152305.3195648-1-memxor@gmail.com
>
>  * Fix bisectability problem by reordering locktorture commit before
>    Makefile commit.
>  * Add EXPORT_SYMBOL_GPL to all used symbols and variables by consumers.
>  * Skip BPF selftest when nrprocs < 2.
>  * Fix kdoc to describe return value for res_spin_lock, slowpath.
>  * Move kernel/locking/rqspinlock.{c,h} to kernel/bpf/rqspinlock.{c,h}.

Applied to bpf-next/res_spin_lock and /for-next branches.

bpf queue_stack, ringbuf, and various local storage-s need to
be converted to res_spin_lock in follow ups.