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Subject[51/78] ALSA: aloop - Fix possible IRQ lock inversion
2.6.38-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Takashi Iwai <tiwai@suse.de>

commit 98d21df431ad55281e1abf780f8d51e3391900b2 upstream.

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>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
sound/drivers/aloop.c | 19 +++++++++----------
1 file changed, 9 insertions(+), 10 deletions(-)
--- a/sound/drivers/aloop.c
+++ b/sound/drivers/aloop.c
@@ -482,8 +482,9 @@ static unsigned int loopback_pos_update(
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(
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(
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;
}




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