The following commit has been merged into the sched/core branch of tip: Commit-ID: e9e5ba93a24d946d6e70d5c85f74254335a6555b Gitweb: https://git.kernel.org/tip/e9e5ba93a24d946d6e70d5c85f74254335a6555b Author: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> AuthorDate: Thu, 26 Aug 2021 19:04:08 +02:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Thu, 09 Sep 2021 11:27:30 +02:00 sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD With PREEMPT_RT enabled all hrtimers callbacks will be invoked in softirq mode unless they are explicitly marked as HRTIMER_MODE_HARD. During boot kthread_bind() is used for the creation of per-CPU threads and then hangs in wait_task_inactive() if the ksoftirqd is not yet up and running. The hang disappeared since commit 26c7295be0c5e ("kthread: Do not preempt current task if it is going to call schedule()") but enabling function trace on boot reliably leads to the freeze on boot behaviour again. The timer in wait_task_inactive() can not be directly used by a user interface to abuse it and create a mass wake up of several tasks at the same time leading to long sections with disabled interrupts. Therefore it is safe to make the timer HRTIMER_MODE_REL_HARD. Switch the timer to HRTIMER_MODE_REL_HARD. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20210826170408.vm7rlj7odslshwch@xxxxxxxxxxxxx --- kernel/sched/core.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a22cc3c..d19d1ba 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3234,7 +3234,7 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state ktime_t to = NSEC_PER_SEC / HZ; set_current_state(TASK_UNINTERRUPTIBLE); - schedule_hrtimeout(&to, HRTIMER_MODE_REL); + schedule_hrtimeout(&to, HRTIMER_MODE_REL_HARD); continue; }
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