ALSA: emux: Fix mutex deadlock in OSS emulation
commit 1c94e65c 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: Jiri Slaby <jslaby@suse.cz>
Showing
Please register or sign in to comment