ALSA: aloop - Fix possible IRQ lock inversion

loopback_pos_update() can be called in the timer callback, thus the lock
held should be irq-safe.  Otherwise you'll get AB/BA deadlock together
with substream->self_group.lock.

Reported-and-tested-by: Knut Petersen <Knut_Petersen@t-online.de>
Cc: <stable@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index 12b44b0..a0da775 100644 (file)
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -482,8 +482,9 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
                        cable->streams[SNDRV_PCM_STREAM_CAPTURE];
        unsigned long delta_play = 0, delta_capt = 0;
        unsigned int running;
+       unsigned long flags;
 
-       spin_lock(&cable->lock);        
+       spin_lock_irqsave(&cable->lock, flags);
        running = cable->running ^ cable->pause;
        if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
                delta_play = jiffies - dpcm_play->last_jiffies;
@@ -495,10 +496,8 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
                dpcm_capt->last_jiffies += delta_capt;
        }
 
-       if (delta_play == 0 && delta_capt == 0) {
-               spin_unlock(&cable->lock);
-               return running;
-       }
+       if (delta_play == 0 && delta_capt == 0)
+               goto unlock;
                
        if (delta_play > delta_capt) {
                loopback_bytepos_update(dpcm_play, delta_play - delta_capt,
@@ -510,14 +509,14 @@ static unsigned int loopback_pos_update(struct loopback_cable *cable)
                delta_capt = delta_play;
        }
 
-       if (delta_play == 0 && delta_capt == 0) {
-               spin_unlock(&cable->lock);
-               return running;
-       }
+       if (delta_play == 0 && delta_capt == 0)
+               goto unlock;
+
        /* note delta_capt == delta_play at this moment */
        loopback_bytepos_update(dpcm_capt, delta_capt, BYTEPOS_UPDATE_COPY);
        loopback_bytepos_update(dpcm_play, delta_play, BYTEPOS_UPDATE_POSONLY);
-       spin_unlock(&cable->lock);
+ unlock:
+       spin_unlock_irqrestore(&cable->lock, flags);
        return running;
 }