linux-kernel - [PATCH RT 09/13] hrtimer: move state change before hrtimer_cancel in do

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Date:   Mon, 07 Jan 2019 14:53:01 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org,
        linux-rt-users <linux-rt-users@...r.kernel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Carsten Emde <C.Emde@...dl.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        John Kacur <jkacur@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Julia Cartwright <julia@...com>,
        Daniel Wagner <daniel.wagner@...mens.com>,
        tom.zanussi@...ux.intel.com, stable-rt@...r.kernel.org,
        Daniel Bristot de Oliveira <bristot@...hat.com>
Subject: [PATCH RT 09/13] hrtimer: move state change before hrtimer_cancel in do_nanosleep()

4.14.87-rt50-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>

[ 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@...r.kernel.org
Reviewed-by: Daniel Bristot de Oliveira <bristot@...hat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 kernel/time/hrtimer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index b59e009087a9..c8d806126381 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1753,12 +1753,12 @@ static int __sched do_nanosleep(struct hrtimer_sleeper *t, enum hrtimer_mode mod
 		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;
-- 
2.19.2