ALSA: emux: Fix mutex deadlock in OSS emulation
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.
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/synth/emux/emux_oss.c b/sound/synth/emux/emux_oss.c
index ab37add..82e350e 100644
--- a/sound/synth/emux/emux_oss.c
+++ b/sound/synth/emux/emux_oss.c
@@ -118,12 +118,8 @@
if (snd_BUG_ON(!arg || !emu))
return -ENXIO;
- mutex_lock(&emu->register_mutex);
-
- if (!snd_emux_inc_count(emu)) {
- mutex_unlock(&emu->register_mutex);
+ if (!snd_emux_inc_count(emu))
return -EFAULT;
- }
memset(&callback, 0, sizeof(callback));
callback.owner = THIS_MODULE;
@@ -135,7 +131,6 @@
if (p == NULL) {
snd_printk(KERN_ERR "can't create port\n");
snd_emux_dec_count(emu);
- mutex_unlock(&emu->register_mutex);
return -ENOMEM;
}
@@ -148,8 +143,6 @@
reset_port_mode(p, arg->seq_mode);
snd_emux_reset_port(p);
-
- mutex_unlock(&emu->register_mutex);
return 0;
}
@@ -195,13 +188,11 @@
if (snd_BUG_ON(!emu))
return -ENXIO;
- mutex_lock(&emu->register_mutex);
snd_emux_sounds_off_all(p);
snd_soundfont_close_check(emu->sflist, SF_CLIENT_NO(p->chset.port));
snd_seq_event_port_detach(p->chset.client, p->chset.port);
snd_emux_dec_count(emu);
- mutex_unlock(&emu->register_mutex);
return 0;
}