Messages in this thread Patch in this message | | | From | Sebastian Andrzej Siewior <> | Subject | [PATCH] sched/core: Schedule new worker even if PI-blocked | Date | Fri, 16 Aug 2019 18:06:26 +0200 |
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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 <bigeasy@linutronix.de> --- kernel/sched/core.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3945,7 +3945,7 @@ 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; /* @@ -3961,6 +3961,9 @@ static inline void sched_submit_work(str 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.
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