Commit 1e568ab9 authored Apr 27, 2015 by Takashi Iwai Committed by Sasha Levin May 17, 2015

ALSA: emux: Fix mutex deadlock at unloading



[ Upstream commit 07b0e5d49d227e3950cb13a3e8caf248ef2a310e ]

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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

parent 3c021baa

sound/synth/emux/emux_seq.c

+0 −2

Original line number	Diff line number	Diff line
		@@ -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);
		}