ALSA: emux: Fix mutex deadlock in OSS emulation

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commit 1c94e65c66 upstream.

The OSS emulation in synth-emux helper has a potential AB/BA deadlock
at the simultaneous closing and opening:

  close ->
    snd_seq_release() ->
      sne_seq_free_client() ->
        snd_seq_delete_all_ports(): takes client->ports_mutex ->
	  port_delete() ->
	    snd_emux_unuse(): takes emux->register_mutex

  open ->
    snd_seq_oss_open() ->
      snd_emux_open_seq_oss(): takes emux->register_mutex ->
        snd_seq_event_port_attach() ->
	  snd_seq_create_port(): takes client->ports_mutex

This patch addresses the deadlock by reducing the rance taking
emux->register_mutex in snd_emux_open_seq_oss().  The lock is needed
for the refcount handling, so move it locally.  The calls in
emux_seq.c are already with the mutex, thus they are replaced with the
version without mutex lock/unlock.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

...

This commit is contained in:

Takashi Iwai 2015-04-28 17:11:44 +02:00 • committed by Luis Henriques

parent 0b7359fb7a

commit 3ffa52f34a

2 changed files with 22 additions and 16 deletions

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11

sound/synth/emux/emux_oss.c

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27

sound/synth/emux/emux_seq.c

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