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>
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@ -3904,7 +3904,7 @@ void __noreturn do_task_dead(void)
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static inline void sched_submit_work(struct task_struct *tsk)
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{
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if (!tsk->state || tsk_is_pi_blocked(tsk))
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if (!tsk->state)
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return;
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/*
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@ -3920,6 +3920,9 @@ static inline void sched_submit_work(struct task_struct *tsk)
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preempt_enable_no_resched();
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}
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if (tsk_is_pi_blocked(tsk))
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return;
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/*
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* If we are going to sleep and we have plugged IO queued,
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* make sure to submit it to avoid deadlocks.
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