[alsa-devel] [PATCH] ALSA: aloop - add locking to timer access

[Takashi Iwai]

At Sat, 29 Sep 2012 12:24:05 +0530,
Omair Mohammed Abdullah wrote:
> 
> 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 at linux.intel.com>
> Signed-off-by: Vinod Koul <vinod.koul at linux.intel.com>

Thanks, applied.


Takashi

> ---
>  sound/drivers/aloop.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
> 
> diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
> index 5a34355..0fe6d64 100644
> --- a/sound/drivers/aloop.c
> +++ b/sound/drivers/aloop.c
> @@ -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) {
> -- 
> 1.7.4.1
>