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authorTakashi Iwai <tiwai@suse.de>2016-01-18 13:52:47 +0100
committerTakashi Iwai <tiwai@suse.de>2016-01-18 14:33:30 +0100
commit2ba1fe7a06d3624f9a7586d672b55f08f7c670f3 (patch)
tree18d95fff22f412e9bab6689314ac4a815551efd1 /sound/core
parentdb8948e653e12b218058bb6696f4a33fa7845f64 (diff)
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 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> Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/core')
-rw-r--r--sound/core/hrtimer.c3
1 files changed, 2 insertions, 1 deletions
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;
}