commit 07b0e5d49d227e3950cb13a3e8caf248ef2a310e
author Takashi Iwai <tiwai@suse.de> Mon Apr 27 14:50:39 2015 +0200
committer Takashi Iwai <tiwai@suse.de> Mon Apr 27 14:50:39 2015 +0200
tree 6051c7e586368aa4bf6c740834e70864307f9bf3
parent d02260824e2cad626fb2a9d62e27006d34b6dedc

ALSA: emux: Fix mutex deadlock at unloading

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.

Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/synth/emux/emux_seq.c

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 @@
 	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);
 }