From: Sebastian Andrzej Siewior bigeasy@linutronix.de
[ Upstream commit b0fdc01354f45d43f082025636ef808968a27b36 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sched/core.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4d5962232a553..42bc2986520d7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3469,7 +3469,7 @@ 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;
/* @@ -3485,6 +3485,9 @@ 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.