[027/151] ALSA: hrtimer - Fix lock-up

Greg KH
2009-12-17T04:44:36Z

From: Takashi Iwai <tiwai@suse.de>

commit fcfdebe70759c74e2e701f69aaa7f0e5e32cf5a6 upstream.

The timer stop callback can be called from snd_timer_interrupt(), which
is called from the hrtimer callback. Since hrtimer_cancel() waits for
the callback completion, this eventually results in a lock-up.

This patch fixes the problem by just toggling a flag at stop callback
and call hrtimer_cancel() later.

Reported-and-tested-by: Wojtek Zabolotny <W.Zabolotny@elka.pw.edu.pl>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
sound/core/hrtimer.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

--- a/sound/core/hrtimer.c
+++ b/sound/core/hrtimer.c
@@ -37,14 +37,22 @@ static unsigned int resolution;
struct snd_hrtimer {
struct snd_timer *timer;
struct hrtimer hrt;
+ atomic_t running;
};

static enum hrtimer_restart snd_hrtimer_callback(struct hrtimer *hrt)
{
struct snd_hrtimer *stime = container_of(hrt, struct snd_hrtimer, hrt);
struct snd_timer *t = stime->timer;
+
+ if (!atomic_read(&stime->running))
+ return HRTIMER_NORESTART;
+
hrtimer_forward_now(hrt, ns_to_ktime(t->sticks * resolution));
snd_timer_interrupt(stime->timer, t->sticks);
+
+ if (!atomic_read(&stime->running))
+ return HRTIMER_NORESTART;
return HRTIMER_RESTART;
}

@@ -58,6 +66,7 @@ static int snd_hrtimer_open(struct snd_t
hrtimer_init(&stime->hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
stime->timer = t;
stime->hrt.function = snd_hrtimer_callback;
+ atomic_set(&stime->running, 0);
t->private_data = stime;
return 0;
}
@@ -78,16 +87,18 @@ static int snd_hrtimer_start(struct snd_
{
struct snd_hrtimer *stime = t->private_data;

+ atomic_set(&stime->running, 0);
+ hrtimer_cancel(&stime->hrt);
hrtimer_start(&stime->hrt, ns_to_ktime(t->sticks * resolution),
HRTIMER_MODE_REL);
+ atomic_set(&stime->running, 1);
return 0;
}

static int snd_hrtimer_stop(struct snd_timer *t)
{
struct snd_hrtimer *stime = t->private_data;
-
- hrtimer_cancel(&stime->hrt);
+ atomic_set(&stime->running, 0);
return 0;
}