[PATCH AUTOSEL 5.10 014/217] bpf: Use separate lockdep class for each hashtab

Sasha Levin
2020-12-23T02:18:13Z

From: Song Liu <songliubraving@fb.com>

[ Upstream commit c50eb518e262fa06bd334e6eec172eaf5d7a5bd9 ]

If a hashtab is accessed in both NMI and non-NMI contexts, it may cause
deadlock in bucket->lock. LOCKDEP NMI warning highlighted this issue:

./test_progs -t stacktrace

[ 74.828970]
[ 74.828971] ================================
[ 74.828972] WARNING: inconsistent lock state
[ 74.828973] 5.9.0-rc8+ #275 Not tainted
[ 74.828974] --------------------------------
[ 74.828975] inconsistent {INITIAL USE} -> {IN-NMI} usage.
[ 74.828976] taskset/1174 [HC2[2]:SC0[0]:HE0:SE1] takes:
[ 74.828977] ffffc90000ee96b0 (&htab->buckets[i].raw_lock){....}-{2:2}, at: htab_map_update_elem+0x271/0x5a0
[ 74.828981] {INITIAL USE} state was registered at:
[ 74.828982] lock_acquire+0x137/0x510
[ 74.828983] _raw_spin_lock_irqsave+0x43/0x90
[ 74.828984] htab_map_update_elem+0x271/0x5a0
[ 74.828984] 0xffffffffa0040b34
[ 74.828985] trace_call_bpf+0x159/0x310
[ 74.828986] perf_trace_run_bpf_submit+0x5f/0xd0
[ 74.828987] perf_trace_urandom_read+0x1be/0x220
[ 74.828988] urandom_read_nowarn.isra.0+0x26f/0x380
[ 74.828989] vfs_read+0xf8/0x280
[ 74.828989] ksys_read+0xc9/0x160
[ 74.828990] do_syscall_64+0x33/0x40
[ 74.828991] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 74.828992] irq event stamp: 1766
[ 74.828993] hardirqs last enabled at (1765): [<ffffffff82800ace>] asm_exc_page_fault+0x1e/0x30
[ 74.828994] hardirqs last disabled at (1766): [<ffffffff8267df87>] irqentry_enter+0x37/0x60
[ 74.828995] softirqs last enabled at (856): [<ffffffff81043e7c>] fpu__clear+0xac/0x120
[ 74.828996] softirqs last disabled at (854): [<ffffffff81043df0>] fpu__clear+0x20/0x120
[ 74.828997]
[ 74.828998] other info that might help us debug this:
[ 74.828999] Possible unsafe locking scenario:
[ 74.828999]
[ 74.829000] CPU0
[ 74.829001] ----
[ 74.829001] lock(&htab->buckets[i].raw_lock);
[ 74.829003] <Interrupt>
[ 74.829004] lock(&htab->buckets[i].raw_lock);
[ 74.829006]
[ 74.829006] *** DEADLOCK ***
[ 74.829007]
[ 74.829008] 1 lock held by taskset/1174:
[ 74.829008] #0: ffff8883ec3fd020 (&cpuctx_lock){-...}-{2:2}, at: perf_event_task_tick+0x101/0x650
[ 74.829012]
[ 74.829013] stack backtrace:
[ 74.829014] CPU: 0 PID: 1174 Comm: taskset Not tainted 5.9.0-rc8+ #275
[ 74.829015] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.11.0-2.el7 04/01/2014
[ 74.829016] Call Trace:
[ 74.829016] <NMI>
[ 74.829017] dump_stack+0x9a/0xd0
[ 74.829018] lock_acquire+0x461/0x510
[ 74.829019] ? lock_release+0x6b0/0x6b0
[ 74.829020] ? stack_map_get_build_id_offset+0x45e/0x800
[ 74.829021] ? htab_map_update_elem+0x271/0x5a0
[ 74.829022] ? rcu_read_lock_held_common+0x1a/0x50
[ 74.829022] ? rcu_read_lock_held+0x5f/0xb0
[ 74.829023] _raw_spin_lock_irqsave+0x43/0x90
[ 74.829024] ? htab_map_update_elem+0x271/0x5a0
[ 74.829025] htab_map_update_elem+0x271/0x5a0
[ 74.829026] bpf_prog_1fd9e30e1438d3c5_oncpu+0x9c/0xe88
[ 74.829027] bpf_overflow_handler+0x127/0x320
[ 74.829028] ? perf_event_text_poke_output+0x4d0/0x4d0
[ 74.829029] ? sched_clock_cpu+0x18/0x130
[ 74.829030] __perf_event_overflow+0xae/0x190
[ 74.829030] handle_pmi_common+0x34c/0x470
[ 74.829031] ? intel_pmu_save_and_restart+0x90/0x90
[ 74.829032] ? lock_acquire+0x3f8/0x510
[ 74.829033] ? lock_release+0x6b0/0x6b0
[ 74.829034] intel_pmu_handle_irq+0x11e/0x240
[ 74.829034] perf_event_nmi_handler+0x40/0x60
[ 74.829035] nmi_handle+0x110/0x360
[ 74.829036] ? __intel_pmu_enable_all.constprop.0+0x72/0xf0
[ 74.829037] default_do_nmi+0x6b/0x170
[ 74.829038] exc_nmi+0x106/0x130
[ 74.829038] end_repeat_nmi+0x16/0x55
[ 74.829039] RIP: 0010:__intel_pmu_enable_all.constprop.0+0x72/0xf0
[ 74.829042] Code: 2f 1f 03 48 8d bb b8 0c 00 00 e8 29 09 41 00 48 ...
[ 74.829043] RSP: 0000:ffff8880a604fc90 EFLAGS: 00000002
[ 74.829044] RAX: 000000070000000f RBX: ffff8883ec2195a0 RCX: 000000000000038f
[ 74.829045] RDX: 0000000000000007 RSI: ffffffff82e72c20 RDI: ffff8883ec21a258
[ 74.829046] RBP: 000000070000000f R08: ffffffff8101b013 R09: fffffbfff0a7982d
[ 74.829047] R10: ffffffff853cc167 R11: fffffbfff0a7982c R12: 0000000000000000
[ 74.829049] R13: ffff8883ec3f0af0 R14: ffff8883ec3fd120 R15: ffff8883e9c92098
[ 74.829049] ? intel_pmu_lbr_enable_all+0x43/0x240
[ 74.829050] ? __intel_pmu_enable_all.constprop.0+0x72/0xf0
[ 74.829051] ? __intel_pmu_enable_all.constprop.0+0x72/0xf0
[ 74.829052] </NMI>
[ 74.829053] perf_event_task_tick+0x48d/0x650
[ 74.829054] scheduler_tick+0x129/0x210
[ 74.829054] update_process_times+0x37/0x70
[ 74.829055] tick_sched_handle.isra.0+0x35/0x90
[ 74.829056] tick_sched_timer+0x8f/0xb0
[ 74.829057] __hrtimer_run_queues+0x364/0x7d0
[ 74.829058] ? tick_sched_do_timer+0xa0/0xa0
[ 74.829058] ? enqueue_hrtimer+0x1e0/0x1e0
[ 74.829059] ? recalibrate_cpu_khz+0x10/0x10
[ 74.829060] ? ktime_get_update_offsets_now+0x1a3/0x360
[ 74.829061] hrtimer_interrupt+0x1bb/0x360
[ 74.829062] ? rcu_read_lock_sched_held+0xa1/0xd0
[ 74.829063] __sysvec_apic_timer_interrupt+0xed/0x3d0
[ 74.829064] sysvec_apic_timer_interrupt+0x3f/0xd0
[ 74.829064] ? asm_sysvec_apic_timer_interrupt+0xa/0x20
[ 74.829065] asm_sysvec_apic_timer_interrupt+0x12/0x20
[ 74.829066] RIP: 0033:0x7fba18d579b4
[ 74.829068] Code: 74 54 44 0f b6 4a 04 41 83 e1 0f 41 80 f9 ...
[ 74.829069] RSP: 002b:00007ffc9ba69570 EFLAGS: 00000206
[ 74.829071] RAX: 00007fba192084c0 RBX: 00007fba18c24d28 RCX: 00000000000007a4
[ 74.829072] RDX: 00007fba18c30488 RSI: 0000000000000000 RDI: 000000000000037b
[ 74.829073] RBP: 00007fba18ca5760 R08: 00007fba18c248fc R09: 00007fba18c94c30
[ 74.829074] R10: 000000000000002f R11: 0000000000073c30 R12: 00007ffc9ba695e0
[ 74.829075] R13: 00000000000003f3 R14: 00007fba18c21ac8 R15: 00000000000058d6

However, such warning should not apply across multiple hashtabs. The
system will not deadlock if one hashtab is used in NMI, while another
hashtab is used in non-NMI.

Use separate lockdep class for each hashtab, so that we don't get this
false alert.

Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20201029071925.3103400-2-songliubraving@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/bpf/hashtab.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 1fccba6e88c4e..224e2652a7c64 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -99,6 +99,7 @@ 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;
};

/* each htab element is struct htab_elem + key + value */
@@ -136,12 +137,18 @@ static void htab_init_buckets(struct bpf_htab *htab)
{
unsigned i;

+ lockdep_register_key(&htab->lockdep_key);
for (i = 0; i < htab->n_buckets; i++) {
INIT_HLIST_NULLS_HEAD(&htab->buckets[i].head, i);
- if (htab_use_raw_lock(htab))
+ if (htab_use_raw_lock(htab)) {
raw_spin_lock_init(&htab->buckets[i].raw_lock);
- else
+ lockdep_set_class(&htab->buckets[i].raw_lock,
+ &htab->lockdep_key);
+ } else {
spin_lock_init(&htab->buckets[i].lock);
+ lockdep_set_class(&htab->buckets[i].lock,
+ &htab->lockdep_key);
+ }
}
}

@@ -1338,6 +1345,7 @@ static void htab_map_free(struct bpf_map *map)

free_percpu(htab->extra_elems);
bpf_map_area_free(htab->buckets);
+ lockdep_unregister_key(&htab->lockdep_key);
kfree(htab);
}

--
2.27.0