From c58157127499876388024179720f201107eef2fe Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 24 Aug 2021 22:47:37 +0200 Subject: [PATCH 300/323] sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.10/older/patches-5.10.215-rt107.tar.xz 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 an user interface to abuse it and create a mass wake of several tasks at the same time which would 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. Cc: stable-rt@vger.kernel.org Link: https://lkml.kernel.org/r/20210826170408.vm7rlj7odslshwch@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt (VMware) --- 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 81b342d6629bb..6735872a8508b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2739,7 +2739,7 @@ unsigned long wait_task_inactive(struct task_struct *p, long 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; } -- 2.44.0