Messages in this thread Patch in this message | | | From | Tom Zanussi <> | Subject | [PATCH RT 4/9] sched/core: Avoid __schedule() being called twice in a row | Date | Fri, 21 Dec 2018 09:21:16 -0600 |
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v3.18.129-rt111 rt-stable review patch. If anyone has any objections, please let me know.
------------------ From: Daniel Bristot de Oliveira <bristot@redhat.com>
[ Upstream commit 2bb94c48b2ffaabf8c15a51e5cc1b4c541988cab ]
If a worker invokes schedule() then we may have the call chain: schedule() -> sched_submit_work() -> wq_worker_sleeping() -> wake_up_worker() -> wake_up_process().
The last wakeup may cause a schedule which is unnecessary because we are already in schedule() and do it anyway.
Add a preempt_disable() + preempt_enable_no_resched() around wq_worker_sleeping() so the context switch could be delayed until __schedule().
Signed-off-by: Daniel Bristot de Oliveira <bristot@redhat.com> Cc: Clark Williams <williams@redhat.com> Cc: Tommaso Cucinotta <tommaso.cucinotta@sssup.it> Cc: Romulo da Silva de Oliveira <romulo.deoliveira@ufsc.br> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar <mingo@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> [bigeasy: rewrite changelog] Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com> --- kernel/sched/core.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d5534f439b4a..500c319fcfc5 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3114,10 +3114,15 @@ static inline void sched_submit_work(struct task_struct *tsk) /* * If a worker went to sleep, notify and ask workqueue whether * it wants to wake up a task to maintain concurrency. + * As this function is called inside the schedule() context, + * we disable preemption to avoid it calling schedule() again + * in the possible wakeup of a kworker. */ - if (tsk->flags & PF_WQ_WORKER) + if (tsk->flags & PF_WQ_WORKER) { + preempt_disable(); wq_worker_sleeping(tsk); - + preempt_enable_no_resched(); + } if (tsk_is_pi_blocked(tsk)) return; -- 2.14.1
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