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authorJohn Sperbeck <jsperbeck@google.com>2019-05-07 18:43:20 -0700
committerDennis Zhou <dennis@kernel.org>2019-05-08 12:08:48 -0700
commit198790d9a3aeaef5792d33a560020861126edc22 (patch)
tree7f2de570f94ef9caf4e5543ceaa6b7c8410f59d8 /mm/percpu.c
parentd33d9f3dd96ba290bad3929f82990a0a7467ae90 (diff)
percpu: remove spurious lock dependency between percpu and sched
In free_percpu() we sometimes call pcpu_schedule_balance_work() to queue a work item (which does a wakeup) while holding pcpu_lock. This creates an unnecessary lock dependency between pcpu_lock and the scheduler's pi_lock. There are other places where we call pcpu_schedule_balance_work() without hold pcpu_lock, and this case doesn't need to be different. Moving the call outside the lock prevents the following lockdep splat when running tools/testing/selftests/bpf/{test_maps,test_progs} in sequence with lockdep enabled: ====================================================== WARNING: possible circular locking dependency detected 5.1.0-dbg-DEV #1 Not tainted ------------------------------------------------------ kworker/23:255/18872 is trying to acquire lock: 000000000bc79290 (&(&pool->lock)->rlock){-.-.}, at: __queue_work+0xb2/0x520 but task is already holding lock: 00000000e3e7a6aa (pcpu_lock){..-.}, at: free_percpu+0x36/0x260 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #4 (pcpu_lock){..-.}: lock_acquire+0x9e/0x180 _raw_spin_lock_irqsave+0x3a/0x50 pcpu_alloc+0xfa/0x780 __alloc_percpu_gfp+0x12/0x20 alloc_htab_elem+0x184/0x2b0 __htab_percpu_map_update_elem+0x252/0x290 bpf_percpu_hash_update+0x7c/0x130 __do_sys_bpf+0x1912/0x1be0 __x64_sys_bpf+0x1a/0x20 do_syscall_64+0x59/0x400 entry_SYSCALL_64_after_hwframe+0x49/0xbe -> #3 (&htab->buckets[i].lock){....}: lock_acquire+0x9e/0x180 _raw_spin_lock_irqsave+0x3a/0x50 htab_map_update_elem+0x1af/0x3a0 -> #2 (&rq->lock){-.-.}: lock_acquire+0x9e/0x180 _raw_spin_lock+0x2f/0x40 task_fork_fair+0x37/0x160 sched_fork+0x211/0x310 copy_process.part.43+0x7b1/0x2160 _do_fork+0xda/0x6b0 kernel_thread+0x29/0x30 rest_init+0x22/0x260 arch_call_rest_init+0xe/0x10 start_kernel+0x4fd/0x520 x86_64_start_reservations+0x24/0x26 x86_64_start_kernel+0x6f/0x72 secondary_startup_64+0xa4/0xb0 -> #1 (&p->pi_lock){-.-.}: lock_acquire+0x9e/0x180 _raw_spin_lock_irqsave+0x3a/0x50 try_to_wake_up+0x41/0x600 wake_up_process+0x15/0x20 create_worker+0x16b/0x1e0 workqueue_init+0x279/0x2ee kernel_init_freeable+0xf7/0x288 kernel_init+0xf/0x180 ret_from_fork+0x24/0x30 -> #0 (&(&pool->lock)->rlock){-.-.}: __lock_acquire+0x101f/0x12a0 lock_acquire+0x9e/0x180 _raw_spin_lock+0x2f/0x40 __queue_work+0xb2/0x520 queue_work_on+0x38/0x80 free_percpu+0x221/0x260 pcpu_freelist_destroy+0x11/0x20 stack_map_free+0x2a/0x40 bpf_map_free_deferred+0x3c/0x50 process_one_work+0x1f7/0x580 worker_thread+0x54/0x410 kthread+0x10f/0x150 ret_from_fork+0x24/0x30 other info that might help us debug this: Chain exists of: &(&pool->lock)->rlock --> &htab->buckets[i].lock --> pcpu_lock Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(pcpu_lock); lock(&htab->buckets[i].lock); lock(pcpu_lock); lock(&(&pool->lock)->rlock); *** DEADLOCK *** 3 locks held by kworker/23:255/18872: #0: 00000000b36a6e16 ((wq_completion)events){+.+.}, at: process_one_work+0x17a/0x580 #1: 00000000dfd966f0 ((work_completion)(&map->work)){+.+.}, at: process_one_work+0x17a/0x580 #2: 00000000e3e7a6aa (pcpu_lock){..-.}, at: free_percpu+0x36/0x260 stack backtrace: CPU: 23 PID: 18872 Comm: kworker/23:255 Not tainted 5.1.0-dbg-DEV #1 Hardware name: ... Workqueue: events bpf_map_free_deferred Call Trace: dump_stack+0x67/0x95 print_circular_bug.isra.38+0x1c6/0x220 check_prev_add.constprop.50+0x9f6/0xd20 __lock_acquire+0x101f/0x12a0 lock_acquire+0x9e/0x180 _raw_spin_lock+0x2f/0x40 __queue_work+0xb2/0x520 queue_work_on+0x38/0x80 free_percpu+0x221/0x260 pcpu_freelist_destroy+0x11/0x20 stack_map_free+0x2a/0x40 bpf_map_free_deferred+0x3c/0x50 process_one_work+0x1f7/0x580 worker_thread+0x54/0x410 kthread+0x10f/0x150 ret_from_fork+0x24/0x30 Signed-off-by: John Sperbeck <jsperbeck@google.com> Signed-off-by: Dennis Zhou <dennis@kernel.org>
Diffstat (limited to 'mm/percpu.c')
-rw-r--r--mm/percpu.c6
1 files changed, 5 insertions, 1 deletions
diff --git a/mm/percpu.c b/mm/percpu.c
index 30e683f42861..7d038393d8f5 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1959,6 +1959,7 @@ void free_percpu(void __percpu *ptr)
struct pcpu_chunk *chunk;
unsigned long flags;
int off;
+ bool need_balance = false;
if (!ptr)
return;
@@ -1980,7 +1981,7 @@ void free_percpu(void __percpu *ptr)
list_for_each_entry(pos, &pcpu_slot[pcpu_nr_slots - 1], list)
if (pos != chunk) {
- pcpu_schedule_balance_work();
+ need_balance = true;
break;
}
}
@@ -1988,6 +1989,9 @@ void free_percpu(void __percpu *ptr)
trace_percpu_free_percpu(chunk->base_addr, off, ptr);
spin_unlock_irqrestore(&pcpu_lock, flags);
+
+ if (need_balance)
+ pcpu_schedule_balance_work();
}
EXPORT_SYMBOL_GPL(free_percpu);