On Mon, Jan 18, 2016 at 2:06 PM, Takashi Iwai tiwai@suse.de wrote:
No, unfortunately the hang still happens with the patch:
Thanks for testing. I think I understood the problem. We faced a similar issue and moved hrtimer_cancel() in the past. But this wasn't enough, as the start function may be called also in interrupt, too.
How about the one below instead?
Yes, this fixes the hang. Thanks!
Tested-by: Dmitry Vyukov dvyukov@google.com
Takashi
From: Takashi Iwai tiwai@suse.de Subject: [PATCH] ALSA: hrtimer: Fix stall by hrtimer_cancel()
hrtimer_cancel() waits for the completion from the callback, thus it must not be called inside the callback itself. This was already a problem, 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 at 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. It's not a hypothetical problem, as 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-by: Dmitry Vyukov dvyukov@google.com Cc: stable@vger.kernel.org Signed-off-by: Takashi Iwai tiwai@suse.de
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 f845ecf7e172..656d9a9032dc 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