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Subject[PATCH 5.2 63/94] sched/core: Schedule new worker even if PI-blocked
[ 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 <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Thomas Gleixner <>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Sasha Levin <>
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)

@@ -3485,6 +3485,9 @@ static inline void sched_submit_work(struct task_struct *tsk)

+ 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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