Messages in this thread Patch in this message | | | From | zanussi@kernel ... | Subject | [PATCH RT 2/8] sched: Switch wait_task_inactive to HRTIMER_MODE_REL_HARD | Date | Wed, 1 Dec 2021 14:41:02 -0600 |
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
v5.4.161-rt67-rc1 stable review patch. If anyone has any objections, please let me know.
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[ Upstream commit 39609ed79d420e0b966e16a1d695733c2d3b9a7f ]
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 <bigeasy@linutronix.de> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Tom Zanussi <zanussi@kernel.org> --- 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 9b32fbded588..022c7b78642d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2158,7 +2158,7 @@ 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; } -- 2.17.1
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