[ 53/84] ALSA: aloop - add locking to timer access

Greg Kroah-Hartman
2012-10-11T02:15:46Z

From: Omair Mohammed Abdullah <omair.m.abdullah@linux.intel.com>

commit d4f1e48bd11e3df6a26811f7a1f06c4225d92f7d upstream.

When the loopback timer handler is running, calling del_timer() (for STOP
trigger) will not wait for the handler to complete before deactivating the
timer. The timer gets rescheduled in the handler as usual. Then a subsequent
START trigger will try to start the timer using add_timer() with a timer pending
leading to a kernel panic.

Serialize the calls to add_timer() and del_timer() using a spin lock to avoid
this.

Signed-off-by: Omair Mohammed Abdullah <omair.m.abdullah@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
sound/drivers/aloop.c | 6 ++++++
1 file changed, 6 insertions(+)

--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -119,6 +119,7 @@ struct loopback_pcm {
unsigned int period_size_frac;
unsigned long last_jiffies;
struct timer_list timer;
+ spinlock_t timer_lock;
};

static struct platform_device *devices[SNDRV_CARDS];
@@ -169,6 +170,7 @@ static void loopback_timer_start(struct
unsigned long tick;
unsigned int rate_shift = get_rate_shift(dpcm);

+ spin_lock(&dpcm->timer_lock);
if (rate_shift != dpcm->pcm_rate_shift) {
dpcm->pcm_rate_shift = rate_shift;
dpcm->period_size_frac = frac_pos(dpcm, dpcm->pcm_period_size);
@@ -181,12 +183,15 @@ static void loopback_timer_start(struct
tick = (tick + dpcm->pcm_bps - 1) / dpcm->pcm_bps;
dpcm->timer.expires = jiffies + tick;
add_timer(&dpcm->timer);
+ spin_unlock(&dpcm->timer_lock);
}

static inline void loopback_timer_stop(struct loopback_pcm *dpcm)
{
+ spin_lock(&dpcm->timer_lock);
del_timer(&dpcm->timer);
dpcm->timer.expires = 0;
+ spin_unlock(&dpcm->timer_lock);
}

#define CABLE_VALID_PLAYBACK (1 << SNDRV_PCM_STREAM_PLAYBACK)
@@ -658,6 +663,7 @@ static int loopback_open(struct snd_pcm_
dpcm->substream = substream;
setup_timer(&dpcm->timer, loopback_timer_function,
(unsigned long)dpcm);
+ spin_lock_init(&dpcm->timer_lock);

cable = loopback->cables[substream->number][dev];
if (!cable) {