From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
tglx@linutronix.de,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: [PATCH] sched/core: Schedule new worker even if PI-blocked
Date: Fri, 16 Aug 2019 18:06:26 +0200 [thread overview]
Message-ID: <20190816160626.12742-1-bigeasy@linutronix.de> (raw)
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.
next reply other threads:[~2019-08-16 16:06 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-16 16:06 Sebastian Andrzej Siewior [this message]
2019-08-19 9:52 ` [tip:sched/urgent] sched/core: Schedule new worker even if PI-blocked tip-bot for Sebastian Andrzej Siewior
2019-08-20 13:50 ` [PATCH] " Peter Zijlstra
2019-08-20 14:59 ` Sebastian Andrzej Siewior
2019-08-20 15:20 ` Peter Zijlstra
2019-08-20 15:54 ` Sebastian Andrzej Siewior
2019-08-20 16:02 ` Peter Zijlstra
2019-08-20 16:14 ` Sebastian Andrzej Siewior
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