linux-kernel - [51/78] ALSA: aloop - Fix possible IRQ lock inversion

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Date:	Mon, 21 Mar 2011 16:02:07 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Takashi Iwai <tiwai@...e.de>
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@...e.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@...nline.de>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.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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