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SubjectRe: possible deadlock in __wake_up_common_lock
On Wed, Jan 02, 2019 at 01:51:01PM +0100, Vlastimil Babka wrote:
> > -> #3 (&base->lock){-.-.}:
> > __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> > _raw_spin_lock_irqsave+0x99/0xd0 kernel/locking/spinlock.c:152
> > lock_timer_base+0xbb/0x2b0 kernel/time/timer.c:937
> > __mod_timer kernel/time/timer.c:1009 [inline]
> > mod_timer kernel/time/timer.c:1101 [inline]
> > add_timer+0x895/0x1490 kernel/time/timer.c:1137
> > __queue_delayed_work+0x249/0x380 kernel/workqueue.c:1533
> > queue_delayed_work_on+0x1a2/0x1f0 kernel/workqueue.c:1558
> > queue_delayed_work include/linux/workqueue.h:527 [inline]
> > schedule_delayed_work include/linux/workqueue.h:628 [inline]
> > psi_group_change kernel/sched/psi.c:485 [inline]
> > psi_task_change+0x3f1/0x5f0 kernel/sched/psi.c:534
> > psi_enqueue kernel/sched/stats.h:82 [inline]
> > enqueue_task kernel/sched/core.c:727 [inline]
> > activate_task+0x21a/0x430 kernel/sched/core.c:751
> > wake_up_new_task+0x527/0xd20 kernel/sched/core.c:2423
> > _do_fork+0x33b/0x11d0 kernel/fork.c:2247
> > kernel_thread+0x34/0x40 kernel/fork.c:2281
> > rest_init+0x28/0x372 init/main.c:409
> > arch_call_rest_init+0xe/0x1b
> > start_kernel+0x873/0x8ae init/main.c:741
> > x86_64_start_reservations+0x29/0x2b arch/x86/kernel/head64.c:470
> > x86_64_start_kernel+0x76/0x79 arch/x86/kernel/head64.c:451
> > secondary_startup_64+0xa4/0xb0 arch/x86/kernel/head_64.S:243

That thing is fairly new; I don't think we used to have this dependency
prior to PSI.

Johannes, can we move that mod_timer out from under rq->lock? At worst
we can use an irq_work to self-ipi.

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