[PATCH 5.4 10/77] sched/deadline: Fix priority inheritance with multiple scheduling classes

Greg Kroah-Hartman
2022-09-02T12:32:55Z

From: Juri Lelli <juri.lelli@redhat.com>

commit 2279f540ea7d05f22d2f0c4224319330228586bc upstream.

Glenn reported that "an application [he developed produces] a BUG in
deadline.c when a SCHED_DEADLINE task contends with CFS tasks on nested
PTHREAD_PRIO_INHERIT mutexes. I believe the bug is triggered when a CFS
task that was boosted by a SCHED_DEADLINE task boosts another CFS task
(nested priority inheritance).

------------[ cut here ]------------
kernel BUG at kernel/sched/deadline.c:1462!
invalid opcode: 0000 [#1] PREEMPT SMP
CPU: 12 PID: 19171 Comm: dl_boost_bug Tainted: ...
Hardware name: ...
RIP: 0010:enqueue_task_dl+0x335/0x910
Code: ...
RSP: 0018:ffffc9000c2bbc68 EFLAGS: 00010002
RAX: 0000000000000009 RBX: ffff888c0af94c00 RCX: ffffffff81e12500
RDX: 000000000000002e RSI: ffff888c0af94c00 RDI: ffff888c10b22600
RBP: ffffc9000c2bbd08 R08: 0000000000000009 R09: 0000000000000078
R10: ffffffff81e12440 R11: ffffffff81e1236c R12: ffff888bc8932600
R13: ffff888c0af94eb8 R14: ffff888c10b22600 R15: ffff888bc8932600
FS: 00007fa58ac55700(0000) GS:ffff888c10b00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa58b523230 CR3: 0000000bf44ab003 CR4: 00000000007606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
PKRU: 55555554
Call Trace:
? intel_pstate_update_util_hwp+0x13/0x170
rt_mutex_setprio+0x1cc/0x4b0
task_blocks_on_rt_mutex+0x225/0x260
rt_spin_lock_slowlock_locked+0xab/0x2d0
rt_spin_lock_slowlock+0x50/0x80
hrtimer_grab_expiry_lock+0x20/0x30
hrtimer_cancel+0x13/0x30
do_nanosleep+0xa0/0x150
hrtimer_nanosleep+0xe1/0x230
? __hrtimer_init_sleeper+0x60/0x60
__x64_sys_nanosleep+0x8d/0xa0
do_syscall_64+0x4a/0x100
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7fa58b52330d
...
---[ end trace 0000000000000002 ]—

He also provided a simple reproducer creating the situation below:

So the execution order of locking steps are the following
(N1 and N2 are non-deadline tasks. D1 is a deadline task. M1 and M2
are mutexes that are enabled * with priority inheritance.)

Time moves forward as this timeline goes down:

N1 N2 D1
| | |
| | |
Lock(M1) | |
| | |
| Lock(M2) |
| | |
| | Lock(M2)
| | |
| Lock(M1) |
| (!!bug triggered!) |

Daniel reported a similar situation as well, by just letting ksoftirqd
run with DEADLINE (and eventually block on a mutex).

Problem is that boosted entities (Priority Inheritance) use static
DEADLINE parameters of the top priority waiter. However, there might be
cases where top waiter could be a non-DEADLINE entity that is currently
boosted by a DEADLINE entity from a different lock chain (i.e., nested
priority chains involving entities of non-DEADLINE classes). In this
case, top waiter static DEADLINE parameters could be null (initialized
to 0 at fork()) and replenish_dl_entity() would hit a BUG().

Fix this by keeping track of the original donor and using its parameters
when a task is boosted.

Reported-by: Glenn Elliott <glenn@aurora.tech>
Reported-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Link: https://lkml.kernel.org/r/20201117061432.517340-1-juri.lelli@redhat.com
[Ankit: Regenerated the patch for v5.4.y]
Signed-off-by: Ankit Jain <ankitja@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/sched.h | 10 ++++
kernel/sched/core.c | 11 ++---
kernel/sched/deadline.c | 97 ++++++++++++++++++++++++++----------------------
3 files changed, 68 insertions(+), 50 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -544,7 +544,6 @@ struct sched_dl_entity {
* overruns.
*/
unsigned int dl_throttled : 1;
- unsigned int dl_boosted : 1;
unsigned int dl_yielded : 1;
unsigned int dl_non_contending : 1;
unsigned int dl_overrun : 1;
@@ -563,6 +562,15 @@ struct sched_dl_entity {
* time.
*/
struct hrtimer inactive_timer;
+
+#ifdef CONFIG_RT_MUTEXES
+ /*
+ * Priority Inheritance. When a DEADLINE scheduling entity is boosted
+ * pi_se points to the donor, otherwise points to the dl_se it belongs
+ * to (the original one/itself).
+ */
+ struct sched_dl_entity *pi_se;
+#endif
};

#ifdef CONFIG_UCLAMP_TASK
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4554,20 +4554,21 @@ void rt_mutex_setprio(struct task_struct
if (!dl_prio(p->normal_prio) ||
(pi_task && dl_prio(pi_task->prio) &&
dl_entity_preempt(&pi_task->dl, &p->dl))) {
- p->dl.dl_boosted = 1;
+ p->dl.pi_se = pi_task->dl.pi_se;
queue_flag |= ENQUEUE_REPLENISH;
- } else
- p->dl.dl_boosted = 0;
+ } else {
+ p->dl.pi_se = &p->dl;
+ }
p->sched_class = &dl_sched_class;
} else if (rt_prio(prio)) {
if (dl_prio(oldprio))
- p->dl.dl_boosted = 0;
+ p->dl.pi_se = &p->dl;
if (oldprio < prio)
queue_flag |= ENQUEUE_HEAD;
p->sched_class = &rt_sched_class;
} else {
if (dl_prio(oldprio))
- p->dl.dl_boosted = 0;
+ p->dl.pi_se = &p->dl;
if (rt_prio(oldprio))
p->rt.timeout = 0;
p->sched_class = &fair_sched_class;
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -43,6 +43,28 @@ static inline int on_dl_rq(struct sched_
return !RB_EMPTY_NODE(&dl_se->rb_node);
}

+#ifdef CONFIG_RT_MUTEXES
+static inline struct sched_dl_entity *pi_of(struct sched_dl_entity *dl_se)
+{
+ return dl_se->pi_se;
+}
+
+static inline bool is_dl_boosted(struct sched_dl_entity *dl_se)
+{
+ return pi_of(dl_se) != dl_se;
+}
+#else
+static inline struct sched_dl_entity *pi_of(struct sched_dl_entity *dl_se)
+{
+ return dl_se;
+}
+
+static inline bool is_dl_boosted(struct sched_dl_entity *dl_se)
+{
+ return false;
+}
+#endif
+
#ifdef CONFIG_SMP
static inline struct dl_bw *dl_bw_of(int i)
{
@@ -657,7 +679,7 @@ static inline void setup_new_dl_entity(s
struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
struct rq *rq = rq_of_dl_rq(dl_rq);

- WARN_ON(dl_se->dl_boosted);
+ WARN_ON(is_dl_boosted(dl_se));
WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));

/*
@@ -695,21 +717,20 @@ static inline void setup_new_dl_entity(s
* could happen are, typically, a entity voluntarily trying to overcome its
* runtime, or it just underestimated it during sched_setattr().
*/
-static void replenish_dl_entity(struct sched_dl_entity *dl_se,
- struct sched_dl_entity *pi_se)
+static void replenish_dl_entity(struct sched_dl_entity *dl_se)
{
struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
struct rq *rq = rq_of_dl_rq(dl_rq);

- BUG_ON(pi_se->dl_runtime <= 0);
+ BUG_ON(pi_of(dl_se)->dl_runtime <= 0);

/*
* This could be the case for a !-dl task that is boosted.
* Just go with full inherited parameters.
*/
if (dl_se->dl_deadline == 0) {
- dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
- dl_se->runtime = pi_se->dl_runtime;
+ dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline;
+ dl_se->runtime = pi_of(dl_se)->dl_runtime;
}

if (dl_se->dl_yielded && dl_se->runtime > 0)
@@ -722,8 +743,8 @@ static void replenish_dl_entity(struct s
* arbitrary large.
*/
while (dl_se->runtime <= 0) {
- dl_se->deadline += pi_se->dl_period;
- dl_se->runtime += pi_se->dl_runtime;
+ dl_se->deadline += pi_of(dl_se)->dl_period;
+ dl_se->runtime += pi_of(dl_se)->dl_runtime;
}

/*
@@ -737,8 +758,8 @@ static void replenish_dl_entity(struct s
*/
if (dl_time_before(dl_se->deadline, rq_clock(rq))) {
printk_deferred_once("sched: DL replenish lagged too much\n");
- dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
- dl_se->runtime = pi_se->dl_runtime;
+ dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline;
+ dl_se->runtime = pi_of(dl_se)->dl_runtime;
}

if (dl_se->dl_yielded)
@@ -771,8 +792,7 @@ static void replenish_dl_entity(struct s
* task with deadline equal to period this is the same of using
* dl_period instead of dl_deadline in the equation above.
*/
-static bool dl_entity_overflow(struct sched_dl_entity *dl_se,
- struct sched_dl_entity *pi_se, u64 t)
+static bool dl_entity_overflow(struct sched_dl_entity *dl_se, u64 t)
{
u64 left, right;

@@ -794,9 +814,9 @@ static bool dl_entity_overflow(struct sc
* of anything below microseconds resolution is actually fiction
* (but still we want to give the user that illusion >;).
*/
- left = (pi_se->dl_deadline >> DL_SCALE) * (dl_se->runtime >> DL_SCALE);
+ left = (pi_of(dl_se)->dl_deadline >> DL_SCALE) * (dl_se->runtime >> DL_SCALE);
right = ((dl_se->deadline - t) >> DL_SCALE) *
- (pi_se->dl_runtime >> DL_SCALE);
+ (pi_of(dl_se)->dl_runtime >> DL_SCALE);

return dl_time_before(right, left);
}
@@ -881,24 +901,23 @@ static inline bool dl_is_implicit(struct
* Please refer to the comments update_dl_revised_wakeup() function to find
* more about the Revised CBS rule.
*/
-static void update_dl_entity(struct sched_dl_entity *dl_se,
- struct sched_dl_entity *pi_se)
+static void update_dl_entity(struct sched_dl_entity *dl_se)
{
struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
struct rq *rq = rq_of_dl_rq(dl_rq);

if (dl_time_before(dl_se->deadline, rq_clock(rq)) ||
- dl_entity_overflow(dl_se, pi_se, rq_clock(rq))) {
+ dl_entity_overflow(dl_se, rq_clock(rq))) {

if (unlikely(!dl_is_implicit(dl_se) &&
!dl_time_before(dl_se->deadline, rq_clock(rq)) &&
- !dl_se->dl_boosted)){
+ !is_dl_boosted(dl_se))) {
update_dl_revised_wakeup(dl_se, rq);
return;
}

- dl_se->deadline = rq_clock(rq) + pi_se->dl_deadline;
- dl_se->runtime = pi_se->dl_runtime;
+ dl_se->deadline = rq_clock(rq) + pi_of(dl_se)->dl_deadline;
+ dl_se->runtime = pi_of(dl_se)->dl_runtime;
}
}

@@ -997,7 +1016,7 @@ static enum hrtimer_restart dl_task_time
* The task might have been boosted by someone else and might be in the
* boosting/deboosting path, its not throttled.
*/
- if (dl_se->dl_boosted)
+ if (is_dl_boosted(dl_se))
goto unlock;

/*
@@ -1025,7 +1044,7 @@ static enum hrtimer_restart dl_task_time
* but do not enqueue -- wait for our wakeup to do that.
*/
if (!task_on_rq_queued(p)) {
- replenish_dl_entity(dl_se, dl_se);
+ replenish_dl_entity(dl_se);
goto unlock;
}

@@ -1115,7 +1134,7 @@ static inline void dl_check_constrained_

if (dl_time_before(dl_se->deadline, rq_clock(rq)) &&
dl_time_before(rq_clock(rq), dl_next_period(dl_se))) {
- if (unlikely(dl_se->dl_boosted || !start_dl_timer(p)))
+ if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(p)))
return;
dl_se->dl_throttled = 1;
if (dl_se->runtime > 0)
@@ -1246,7 +1265,7 @@ throttle:
dl_se->dl_overrun = 1;

__dequeue_task_dl(rq, curr, 0);
- if (unlikely(dl_se->dl_boosted || !start_dl_timer(curr)))
+ if (unlikely(is_dl_boosted(dl_se) || !start_dl_timer(curr)))
enqueue_task_dl(rq, curr, ENQUEUE_REPLENISH);

if (!is_leftmost(curr, &rq->dl))
@@ -1440,8 +1459,7 @@ static void __dequeue_dl_entity(struct s
}

static void
-enqueue_dl_entity(struct sched_dl_entity *dl_se,
- struct sched_dl_entity *pi_se, int flags)
+enqueue_dl_entity(struct sched_dl_entity *dl_se, int flags)
{
BUG_ON(on_dl_rq(dl_se));

@@ -1452,9 +1470,9 @@ enqueue_dl_entity(struct sched_dl_entity
*/
if (flags & ENQUEUE_WAKEUP) {
task_contending(dl_se, flags);
- update_dl_entity(dl_se, pi_se);
+ update_dl_entity(dl_se);
} else if (flags & ENQUEUE_REPLENISH) {
- replenish_dl_entity(dl_se, pi_se);
+ replenish_dl_entity(dl_se);
} else if ((flags & ENQUEUE_RESTORE) &&
dl_time_before(dl_se->deadline,
rq_clock(rq_of_dl_rq(dl_rq_of_se(dl_se))))) {
@@ -1471,19 +1489,7 @@ static void dequeue_dl_entity(struct sch

static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
{
- struct task_struct *pi_task = rt_mutex_get_top_task(p);
- struct sched_dl_entity *pi_se = &p->dl;
-
- /*
- * Use the scheduling parameters of the top pi-waiter task if:
- * - we have a top pi-waiter which is a SCHED_DEADLINE task AND
- * - our dl_boosted is set (i.e. the pi-waiter's (absolute) deadline is
- * smaller than our deadline OR we are a !SCHED_DEADLINE task getting
- * boosted due to a SCHED_DEADLINE pi-waiter).
- * Otherwise we keep our runtime and deadline.
- */
- if (pi_task && dl_prio(pi_task->normal_prio) && p->dl.dl_boosted) {
- pi_se = &pi_task->dl;
+ if (is_dl_boosted(&p->dl)) {
/*
* Because of delays in the detection of the overrun of a
* thread's runtime, it might be the case that a thread
@@ -1516,7 +1522,7 @@ static void enqueue_task_dl(struct rq *r
* the throttle.
*/
p->dl.dl_throttled = 0;
- BUG_ON(!p->dl.dl_boosted || flags != ENQUEUE_REPLENISH);
+ BUG_ON(!is_dl_boosted(&p->dl) || flags != ENQUEUE_REPLENISH);
return;
}

@@ -1553,7 +1559,7 @@ static void enqueue_task_dl(struct rq *r
return;
}

- enqueue_dl_entity(&p->dl, pi_se, flags);
+ enqueue_dl_entity(&p->dl, flags);

if (!task_current(rq, p) && p->nr_cpus_allowed > 1)
enqueue_pushable_dl_task(rq, p);
@@ -2722,11 +2728,14 @@ void __dl_clear_params(struct task_struc
dl_se->dl_bw = 0;
dl_se->dl_density = 0;

- dl_se->dl_boosted = 0;
dl_se->dl_throttled = 0;
dl_se->dl_yielded = 0;
dl_se->dl_non_contending = 0;
dl_se->dl_overrun = 0;
+
+#ifdef CONFIG_RT_MUTEXES
+ dl_se->pi_se = dl_se;
+#endif
}

bool dl_param_changed(struct task_struct *p, const struct sched_attr *attr)