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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 6 Dec 2018 10:15:13 +0100
Subject: [PATCH] hrtimer: move state change before hrtimer_cancel in
do_nanosleep()
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.2/older/patches-5.2.10-rt5.tar.xz
There is a small window between setting t->task to NULL and waking the
task up (which would set TASK_RUNNING). So the timer would fire, run and
set ->task to NULL while the other side/do_nanosleep() wouldn't enter
freezable_schedule(). After all we are peemptible here (in
do_nanosleep() and on the timer wake up path) and on KVM/virt the
virt-CPU might get preempted.
So do_nanosleep() wouldn't enter freezable_schedule() but cancel the
timer which is still running and wait for it via
hrtimer_wait_for_timer(). Then wait_event()/might_sleep() would complain
that it is invoked with state != TASK_RUNNING.
This isn't a problem since it would be reset to TASK_RUNNING later
anyway and we don't rely on the previous state.
Move the state update to TASK_RUNNING before hrtimer_cancel() so there
are no complains from might_sleep() about wrong state.
Cc: stable-rt@vger.kernel.org
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/time/hrtimer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1736,12 +1736,12 @@ static int __sched do_nanosleep(struct h
if (likely(t->task))
freezable_schedule();
+ __set_current_state(TASK_RUNNING);
hrtimer_cancel(&t->timer);
mode = HRTIMER_MODE_ABS;
} while (t->task && !signal_pending(current));
- __set_current_state(TASK_RUNNING);
if (!t->task)
return 0;
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