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From f29a6f7bb4568b4ac2d5a9226d503db7a2c69bab Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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-5.10.204-rt100.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 <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.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 81b342d6629b..6735872a8508 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;
}
--
2.43.0
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