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sched/core: Schedule new worker even if PI-blocked

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If a task is PI-blocked (blocking on sleeping spinlock) then we don't want to
schedule a new kworker if we schedule out due to lock contention because !RT
does not do that as well. A spinning spinlock disables preemption and a worker
does not schedule out on lock contention (but spin).

On RT the RW-semaphore implementation uses an rtmutex so
tsk_is_pi_blocked() will return true if a task blocks on it. In this case we
will now start a new worker which may deadlock if one worker is waiting on
progress from another worker. Since a RW-semaphore starts a new worker on !RT,
we should do the same on RT.

XFS is able to trigger this deadlock.

Allow to schedule new worker if the current worker is PI-blocked.

Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Sebastian Andrzej Siewior 2019-08-16 18:06:26 +02:00 • committed by Ingo Molnar
commit b0fdc01354
1 changed files with 4 additions and 1 deletions
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5
kernel/sched/core.c
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@ -3904,7 +3904,7 @@ void __noreturn do_task_dead(void)
static inline void sched_submit_work(struct task_struct *tsk)
{
if (!tsk->state || tsk_is_pi_blocked(tsk))
if (!tsk->state)
return;
/*
@ -3920,6 +3920,9 @@ static inline void sched_submit_work(struct task_struct *tsk)
preempt_enable_no_resched();
}
if (tsk_is_pi_blocked(tsk))
return;
/*
* If we are going to sleep and we have plugged IO queued,
* make sure to submit it to avoid deadlocks.