From: luca abeni <luca.abeni@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Acked-by: Juri Lelli <juri.lelli@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: chengjian (D) <cj.chengjian@xxxxxxxxxx> Link: https://lkml.kernel.org/r/20190325131530.34706-1-luca.abeni@xxxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/sched/deadline.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -217,7 +217,6 @@ static void task_non_contending(struct t if (dl_se->dl_runtime == 0) return; - WARN_ON(hrtimer_active(&dl_se->inactive_timer)); WARN_ON(dl_se->dl_non_contending); zerolag_time = dl_se->deadline - @@ -234,7 +233,7 @@ 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_bw, dl_rq); if (!dl_task(p) || p->state == TASK_DEAD) {
