ALSA: snd-aloop - fix locking issues (running flag updates)

On SMP machines, the cable->running update must be atomic, otherwise
stream is not started correctly sometimes.

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

1 files changed, 19 insertions, 13 deletions

diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
index 66786ea6f480..38e8351e935d 100644
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -263,13 +263,17 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd)
                         return err;
                 dpcm->last_jiffies = jiffies;
                 dpcm->pcm_rate_shift = 0;
-                loopback_timer_start(dpcm);
+                spin_lock(&cable->lock);        
                 cable->running |= (1 << substream->stream);
+                spin_unlock(&cable->lock);
+                loopback_timer_start(dpcm);
                 if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
                         loopback_active_notify(dpcm);
                 break;
         case SNDRV_PCM_TRIGGER_STOP:
+                spin_lock(&cable->lock);        
                 cable->running &= ~(1 << substream->stream);
+                spin_unlock(&cable->lock);
                 loopback_timer_stop(dpcm);
                 if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
                         loopback_active_notify(dpcm);
@@ -454,28 +458,30 @@ static void loopback_bytepos_update(struct loopback_pcm *dpcm,
         }
 }
 
-static void loopback_pos_update(struct loopback_cable *cable)
+static unsigned int loopback_pos_update(struct loopback_cable *cable)
 {
         struct loopback_pcm *dpcm_play =
                         cable->streams[SNDRV_PCM_STREAM_PLAYBACK];
         struct loopback_pcm *dpcm_capt =
                         cable->streams[SNDRV_PCM_STREAM_CAPTURE];
         unsigned long delta_play = 0, delta_capt = 0;
+        unsigned int running;
 
         spin_lock(&cable->lock);        
-        if (cable->running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
+        running = cable->running;
+        if (running & (1 << SNDRV_PCM_STREAM_PLAYBACK)) {
                 delta_play = jiffies - dpcm_play->last_jiffies;
                 dpcm_play->last_jiffies += delta_play;
         }
 
-        if (cable->running & (1 << SNDRV_PCM_STREAM_CAPTURE)) {
+        if (running & (1 << SNDRV_PCM_STREAM_CAPTURE)) {
                 delta_capt = jiffies - dpcm_capt->last_jiffies;
                 dpcm_capt->last_jiffies += delta_capt;
         }
 
         if (delta_play == 0 && delta_capt == 0) {
                 spin_unlock(&cable->lock);
-                return;
+                return running;
         }
                 
         if (delta_play > delta_capt) {
@@ -490,27 +496,27 @@ static void loopback_pos_update(struct loopback_cable *cable)
 
         if (delta_play == 0 && delta_capt == 0) {
                 spin_unlock(&cable->lock);
-                return;
+                return running;
         }
         /* 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);
+        return running;
 }
 
 static void loopback_timer_function(unsigned long data)
 {
         struct loopback_pcm *dpcm = (struct loopback_pcm *)data;
-        int stream;
+        unsigned int running;
 
-        loopback_pos_update(dpcm->cable);
-        stream = dpcm->substream->stream;
-        if (dpcm->cable->running & (1 << stream))
+        running = loopback_pos_update(dpcm->cable);
+        if (running & (1 << dpcm->substream->stream)) {
                 loopback_timer_start(dpcm);
-        if (dpcm->period_update_pending) {
-                dpcm->period_update_pending = 0;
-                if (dpcm->cable->running & (1 << stream))
+                if (dpcm->period_update_pending) {
+                        dpcm->period_update_pending = 0;
                         snd_pcm_period_elapsed(dpcm->substream);
+                }
         }
 }