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ALSA: aloop - add locking to timer access 

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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Omair Mohammed Abdullah 2012-09-29 12:24:05 +05:30 committed by Takashi Iwai
parent d17344b354
commit d4f1e48bd1
1 changed files with 6 additions and 0 deletions
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6
sound/drivers/aloop.c
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@ -120,6 +120,7 @@ struct loopback_pcm {
unsigned int last_drift;
unsigned long last_jiffies;
struct timer_list timer;
spinlock_t timer_lock;
};
static struct platform_device *devices[SNDRV_CARDS];
@ -170,6 +171,7 @@ static void loopback_timer_start(struct loopback_pcm *dpcm)
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);
@ -182,12 +184,15 @@ static void loopback_timer_start(struct loopback_pcm *dpcm)
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)
@ -667,6 +672,7 @@ static int loopback_open(struct snd_pcm_substream *substream)
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) {