| From 2ba1fe7a06d3624f9a7586d672b55f08f7c670f3 Mon Sep 17 00:00:00 2001 |
| From: Takashi Iwai <tiwai@suse.de> |
| Date: Mon, 18 Jan 2016 13:52:47 +0100 |
| Subject: ALSA: hrtimer: Fix stall by hrtimer_cancel() |
| |
| From: Takashi Iwai <tiwai@suse.de> |
| |
| 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@google.com> |
| Signed-off-by: Takashi Iwai <tiwai@suse.de> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| sound/core/hrtimer.c | 3 ++- |
| 1 file changed, 2 insertions(+), 1 deletion(-) |
| |
| --- a/sound/core/hrtimer.c |
| +++ b/sound/core/hrtimer.c |
| @@ -90,7 +90,7 @@ static int snd_hrtimer_start(struct snd_ |
| 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_t |
| { |
| struct snd_hrtimer *stime = t->private_data; |
| atomic_set(&stime->running, 0); |
| + hrtimer_try_to_cancel(&stime->hrt); |
| return 0; |
| } |
| |
