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Commit 245a94a0 authored by luca abeni's avatar luca abeni Committed by Greg Kroah-Hartman
Browse files

sched/deadline: Correctly handle active 0-lag timers 



commit 1b02cd6a2d7f3e2a6a5262887d2cb2912083e42f upstream.

syzbot reported the following warning:

   [ ] WARNING: CPU: 4 PID: 17089 at kernel/sched/deadline.c:255 task_non_contending+0xae0/0x1950

line 255 of deadline.c is:

	WARN_ON(hrtimer_active(&dl_se->inactive_timer));

in task_non_contending().

Unfortunately, in some cases (for example, a deadline task
continuosly blocking and waking immediately) it can happen that
a task blocks (and task_non_contending() is called) while the
0-lag timer is still active.

In this case, the safest thing to do is to immediately decrease
the running bandwidth of the task, without trying to re-arm the 0-lag timer.

Signed-off-by: default avatarluca abeni <luca.abeni@santannapisa.it>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarJuri Lelli <juri.lelli@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: chengjian (D) <cj.chengjian@huawei.com>
Link: https://lkml.kernel.org/r/20190325131530.34706-1-luca.abeni@santannapisa.it


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 6bf7d3c5

kernel/sched/deadline.c

+1 −2
Original line number Diff line number Diff line
@@ -252,7 +252,6 @@ static void task_non_contending(struct task_struct *p) 
	if (dl_entity_is_special(dl_se))

		return;



	WARN_ON(hrtimer_active(&dl_se->inactive_timer));

	WARN_ON(dl_se->dl_non_contending);



	zerolag_time = dl_se->deadline -
@@ -269,7 +268,7 @@ static void task_non_contending(struct task_struct *p) 
	 * If the "0-lag time" already passed, decrease the active

	 * utilization now, instead of starting a timer

	 */

	if (zerolag_time < 0) {

	if ((zerolag_time < 0) || hrtimer_active(&dl_se->inactive_timer)) {

		if (dl_task(p))

			sub_running_bw(dl_se, dl_rq);

		if (!dl_task(p) || p->state == TASK_DEAD) {