workqueue: Fix unbind_workers() VS wq_worker_sleeping() race
At CPU-hotplug time, unbind_workers() may preempt a worker while it is
going to sleep. In that case the following scenario can happen:
unbind_workers() wq_worker_sleeping()
-------------- -------------------
if (worker->flags & WORKER_NOT_RUNNING)
return;
//PREEMPTED by unbind_workers
worker->flags |= WORKER_UNBOUND;
[...]
atomic_set(&pool->nr_running, 0);
//resume to worker
atomic_dec_and_test(&pool->nr_running);
After unbind_worker() resets pool->nr_running, the value is expected to
remain 0 until the pool ever gets rebound in case cpu_up() is called on
the target CPU in the future. But here the race leaves pool->nr_running
with a value of -1, triggering the following warning when the worker goes
idle:
WARNING: CPU: 3 PID: 34 at kernel/workqueue.c:1823 worker_enter_idle+0x95/0xc0
Modules linked in:
CPU: 3 PID: 34 Comm: kworker/3:0 Not tainted 5.16.0-rc1+ #34
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
Workqueue: 0x0 (rcu_par_gp)
RIP: 0010:worker_enter_idle+0x95/0xc0
Code: 04 85 f8 ff ff ff 39 c1 7f 09 48 8b 43 50 48 85 c0 74 1b 83 e2 04 75 99 8b 43 34 39 43 30 75 91 8b 83 00 03 00 00 85 c0 74 87 <0f> 0b 5b c3 48 8b 35 70 f1 37 01 48 8d 7b 48 48 81 c6 e0 93 0
RSP: 0000:
ffff9b7680277ed0 EFLAGS:
00010086
RAX:
00000000ffffffff RBX:
ffff93465eae9c00 RCX:
0000000000000000
RDX:
0000000000000000 RSI:
ffff9346418a0000 RDI:
ffff934641057140
RBP:
ffff934641057170 R08:
0000000000000001 R09:
ffff9346418a0080
R10:
ffff9b768027fdf0 R11:
0000000000002400 R12:
ffff93465eae9c20
R13:
ffff93465eae9c20 R14:
ffff93465eae9c70 R15:
ffff934641057140
FS:
0000000000000000(0000) GS:
ffff93465eac0000(0000) knlGS:
0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0:
0000000080050033
CR2:
0000000000000000 CR3:
000000001cc0c000 CR4:
00000000000006e0
DR0:
0000000000000000 DR1:
0000000000000000 DR2:
0000000000000000
DR3:
0000000000000000 DR6:
00000000fffe0ff0 DR7:
0000000000000400
Call Trace:
<TASK>
worker_thread+0x89/0x3d0
? process_one_work+0x400/0x400
kthread+0x162/0x190
? set_kthread_struct+0x40/0x40
ret_from_fork+0x22/0x30
</TASK>
Also due to this incorrect "nr_running == -1", all sorts of hazards can
happen, starting with queued works being ignored because no workers are
awaken at insert_work() time.
Fix this with checking again the worker flags while pool->lock is locked.
Fixes:
b945efcdd07d ("sched: Remove pointless preemption disable in sched_submit_work()")
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>