From: Takashi Iwai <tiwai@xxxxxxx> This patch has been added to the 3.12 stable tree. If you have any objections, please let us know. =============== commit 2ba1fe7a06d3624f9a7586d672b55f08f7c670f3 upstream. hrtimer_cancel() waits for the completion from the callback, thus it must not be called inside the callback itself. This was already a problem in the past with ALSA hrtimer driver, and the early commit [fcfdebe70759: ALSA: hrtimer - Fix lock-up] tried to address it. However, the previous fix is still insufficient: it may still cause a lockup when the ALSA timer instance reprograms itself in its callback. Then it invokes the start function even in snd_timer_interrupt() that is called in hrtimer callback itself, results in a CPU stall. This is no hypothetical problem but actually triggered by syzkaller fuzzer. This patch tries to fix the issue again. Now we call hrtimer_try_to_cancel() at both start and stop functions so that it won't fall into a deadlock, yet giving some chance to cancel the queue if the functions have been called outside the callback. The proper hrtimer_cancel() is called in anyway at closing, so this should be enough. Reported-and-tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> Signed-off-by: Jiri Slaby <jslaby@xxxxxxx> --- sound/core/hrtimer.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/sound/core/hrtimer.c b/sound/core/hrtimer.c index b8b31c433d64..14d483d6b3b0 100644 --- a/sound/core/hrtimer.c +++ b/sound/core/hrtimer.c @@ -90,7 +90,7 @@ static int snd_hrtimer_start(struct snd_timer *t) struct snd_hrtimer *stime = t->private_data; atomic_set(&stime->running, 0); - hrtimer_cancel(&stime->hrt); + hrtimer_try_to_cancel(&stime->hrt); hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution), HRTIMER_MODE_REL); atomic_set(&stime->running, 1); @@ -101,6 +101,7 @@ static int snd_hrtimer_stop(struct snd_timer *t) { struct snd_hrtimer *stime = t->private_data; atomic_set(&stime->running, 0); + hrtimer_try_to_cancel(&stime->hrt); return 0; } -- 2.7.0 -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html