From: luca abeni luca.abeni@santannapisa.it
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: luca abeni luca.abeni@santannapisa.it Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Acked-by: Juri 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: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/sched/deadline.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -252,7 +252,6 @@ static void task_non_contending(struct t 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 t * 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) {