From: Takashi Iwai <tiwai@suse.de>
Date: Tue, 28 Apr 2015 15:11:44 +0000 (+0200)
Subject: ALSA: emux: Fix mutex deadlock in OSS emulation
X-Git-Tag: v3.2.70~102
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f696aa6f0c43ba1c180b28e4e895ef005092d331;p=pandora-kernel.git

ALSA: emux: Fix mutex deadlock in OSS emulation

commit 1c94e65c668f44d2c69ae7e7fc268ab3268fba3e 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: Ben Hutchings <ben@decadent.org.uk>
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