Commit b0fdc013 authored Aug 16, 2019 by Sebastian Andrzej Siewior Committed by Ingo Molnar Aug 19, 2019

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



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 <bigeasy@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20190816160626.12742-1-bigeasy@linutronix.de


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent d1abaeb3

kernel/sched/core.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -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.