[3.13.y.z extended stable] Patch "ALSA: emu10k1: Fix deadlock in synth voice lookup" has been added to staging queue

Kamal Mostafa kamal at canonical.com
Tue Oct 21 20:09:33 UTC 2014


This is a note to let you know that I have just added a patch titled

    ALSA: emu10k1: Fix deadlock in synth voice lookup

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.10.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From cfec8447213cf997da0d2e7eee50389b2a8a12a4 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai at suse.de>
Date: Mon, 13 Oct 2014 23:18:02 +0200
Subject: ALSA: emu10k1: Fix deadlock in synth voice lookup

commit 95926035b187cc9fee6fb61385b7da9c28123f74 upstream.

The emu10k1 voice allocator takes voice_lock spinlock.  When there is
no empty stream available, it tries to release a voice used by synth,
and calls get_synth_voice.  The callback function,
snd_emu10k1_synth_get_voice(), however, also takes the voice_lock,
thus it deadlocks.

The fix is simply removing the voice_lock holds in
snd_emu10k1_synth_get_voice(), as this is always called in the
spinlock context.

Reported-and-tested-by: Arthur Marsh <arthur.marsh at internode.on.net>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 sound/pci/emu10k1/emu10k1_callback.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/sound/pci/emu10k1/emu10k1_callback.c b/sound/pci/emu10k1/emu10k1_callback.c
index cae3659..0a34b5f 100644
--- a/sound/pci/emu10k1/emu10k1_callback.c
+++ b/sound/pci/emu10k1/emu10k1_callback.c
@@ -85,6 +85,8 @@ snd_emu10k1_ops_setup(struct snd_emux *emux)
  * get more voice for pcm
  *
  * terminate most inactive voice and give it as a pcm voice.
+ *
+ * voice_lock is already held.
  */
 int
 snd_emu10k1_synth_get_voice(struct snd_emu10k1 *hw)
@@ -92,12 +94,10 @@ snd_emu10k1_synth_get_voice(struct snd_emu10k1 *hw)
 	struct snd_emux *emu;
 	struct snd_emux_voice *vp;
 	struct best_voice best[V_END];
-	unsigned long flags;
 	int i;

 	emu = hw->synth;

-	spin_lock_irqsave(&emu->voice_lock, flags);
 	lookup_voices(emu, hw, best, 1); /* no OFF voices */
 	for (i = 0; i < V_END; i++) {
 		if (best[i].voice >= 0) {
@@ -113,11 +113,9 @@ snd_emu10k1_synth_get_voice(struct snd_emu10k1 *hw)
 			vp->emu->num_voices--;
 			vp->ch = -1;
 			vp->state = SNDRV_EMUX_ST_OFF;
-			spin_unlock_irqrestore(&emu->voice_lock, flags);
 			return ch;
 		}
 	}
-	spin_unlock_irqrestore(&emu->voice_lock, flags);

 	/* not found */
 	return -ENOMEM;
--
1.9.1





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