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ALSA: emux: Fix mutex deadlock in OSS emulation 

commit 1c94e65c66 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Takashi Iwai 2015-04-28 17:11:44 +02:00 committed by Greg Kroah-Hartman
parent 637eb000c8
commit b5834d888a
2 changed files with 22 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
sound/synth/emux/emux_oss.c
View File

@ -118,12 +118,8 @@ snd_emux_open_seq_oss(struct snd_seq_oss_arg *arg, void *closure)
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 @@ snd_emux_open_seq_oss(struct snd_seq_oss_arg *arg, void *closure)
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 @@ snd_emux_open_seq_oss(struct snd_seq_oss_arg *arg, void *closure)
reset_port_mode(p, arg->seq_mode);
snd_emux_reset_port(p);
mutex_unlock(&emu->register_mutex);
return 0;
}
@ -195,13 +188,11 @@ snd_emux_close_seq_oss(struct snd_seq_oss_arg *arg)
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;
}

27
sound/synth/emux/emux_seq.c
View File

@ -267,8 +267,8 @@ snd_emux_event_input(struct snd_seq_event *ev, int direct, void *private_data,
/*
* increment usage count
*/
int
snd_emux_inc_count(struct snd_emux *emu)
static int
__snd_emux_inc_count(struct snd_emux *emu)
{
emu->used++;
if (!try_module_get(emu->ops.owner))
@ -282,12 +282,21 @@ snd_emux_inc_count(struct snd_emux *emu)
return 1;
}
int snd_emux_inc_count(struct snd_emux *emu)
{
int ret;
mutex_lock(&emu->register_mutex);
ret = __snd_emux_inc_count(emu);
mutex_unlock(&emu->register_mutex);
return ret;
}
/*
* decrease usage count
*/
void
snd_emux_dec_count(struct snd_emux *emu)
static void
__snd_emux_dec_count(struct snd_emux *emu)
{
module_put(emu->card->module);
emu->used--;
@ -296,6 +305,12 @@ snd_emux_dec_count(struct snd_emux *emu)
module_put(emu->ops.owner);
}
void snd_emux_dec_count(struct snd_emux *emu)
{
mutex_lock(&emu->register_mutex);
__snd_emux_dec_count(emu);
mutex_unlock(&emu->register_mutex);
}
/*
* Routine that is called upon a first use of a particular port
@ -315,7 +330,7 @@ snd_emux_use(void *private_data, struct snd_seq_port_subscribe *info)
mutex_lock(&emu->register_mutex);
snd_emux_init_port(p);
snd_emux_inc_count(emu);
__snd_emux_inc_count(emu);
mutex_unlock(&emu->register_mutex);
return 0;
}
@ -338,7 +353,7 @@ snd_emux_unuse(void *private_data, struct snd_seq_port_subscribe *info)
mutex_lock(&emu->register_mutex);
snd_emux_sounds_off_all(p);
snd_emux_dec_count(emu);
__snd_emux_dec_count(emu);
mutex_unlock(&emu->register_mutex);
return 0;
}