From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Thu, 6 Dec 2018 10:15:13 +0100
Subject: hrtimer: move state change before hrtimer_cancel in do_nanosleep()
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 482a6a49795d22259cdcbd1dc8d8394a0562ad61
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension
[ Upstream commit 8115ac730fd5aa27134f002cf710204b5dd7cd5e ]
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>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
kernel/time/hrtimer.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1734,12 +1734,12 @@ 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;