linux-kernel - [PATCH 3.4 058/146] ALSA: emux: Fix mutex deadlock at unloading

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Date:	Tue, 15 Sep 2015 17:02:53 +0800
From:	lizf@...nel.org
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Takashi Iwai <tiwai@...e.de>,
	Zefan Li <lizefan@...wei.com>
Subject: [PATCH 3.4 058/146] ALSA: emux: Fix mutex deadlock at unloading

From: Takashi Iwai <tiwai@...e.de>

3.4.109-rc1 review patch.  If anyone has any objections, please let me know.

------------------


commit 07b0e5d49d227e3950cb13a3e8caf248ef2a310e upstream.

The emux-synth driver has a possible AB/BA mutex deadlock at unloading
the emu10k1 driver:

  snd_emux_free() ->
    snd_emux_detach_seq(): mutex_lock(&emu->register_mutex) ->
      snd_seq_delete_kernel_client() ->
        snd_seq_free_client(): mutex_lock(&register_mutex)

  snd_seq_release() ->
    snd_seq_free_client(): mutex_lock(&register_mutex) ->
      snd_seq_delete_all_ports() ->
        snd_emux_unuse(): mutex_lock(&emu->register_mutex)

Basically snd_emux_detach_seq() doesn't need a protection of
emu->register_mutex as it's already being unregistered.  So, we can
get rid of this for avoiding the deadlock.

Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Zefan Li <lizefan@...wei.com>
---
 sound/synth/emux/emux_seq.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/sound/synth/emux/emux_seq.c b/sound/synth/emux/emux_seq.c
index 7778b8e..188fda0e 100644
--- a/sound/synth/emux/emux_seq.c
+++ b/sound/synth/emux/emux_seq.c
@@ -124,12 +124,10 @@ snd_emux_detach_seq(struct snd_emux *emu)
 	if (emu->voices)
 		snd_emux_terminate_all(emu);
 		
-	mutex_lock(&emu->register_mutex);
 	if (emu->client >= 0) {
 		snd_seq_delete_kernel_client(emu->client);
 		emu->client = -1;
 	}
-	mutex_unlock(&emu->register_mutex);
 }
 
 
-- 
1.9.1

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