ALSA: emux: Fix mutex deadlock at unloading
authorTakashi Iwai <tiwai@suse.de>
Mon, 27 Apr 2015 12:50:39 +0000 (14:50 +0200)
committerBen Hutchings <ben@decadent.org.uk>
Thu, 6 Aug 2015 23:32:07 +0000 (00:32 +0100)
commitb14b5688328d7c3af29afe4aa3b65c4be36706b2
tree7928e75e8059c06371b373873dc24b23bd645746
parent172210296cc6debd42698165f1999a384d008fa3
ALSA: emux: Fix mutex deadlock at unloading

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@suse.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
sound/synth/emux/emux_seq.c