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pcm: Disable locking in async mode

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When PCM is operated in async mode and an async handler calls some PCM
functions with lock during other PCM operations, we may hit a
deadlock.

Although async mode is rarely used, it's still a possible use case.
Disable the locking when the stream is opened in async mode or it's
set to async mode via snd_pcm_async().

Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2017-02-09 17:29:21 +01:00
parent b5a2c06f6c
commit e31a3273df
1 changed files with 6 additions and 1 deletions
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7
src/pcm/pcm.c
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@ -799,6 +799,8 @@ int snd_pcm_async(snd_pcm_t *pcm, int sig, pid_t pid)
sig = SIGIO;
if (pid == 0)
pid = getpid();
/* async handler may lead to a deadlock; suppose no multi thread */
pcm->lock_enabled = 0;
return pcm->ops->async(pcm->op_arg, sig, pid);
}
#endif
@ -2597,7 +2599,10 @@ int snd_pcm_new(snd_pcm_t **pcmp, snd_pcm_type_t type, const char *name,
* each plugin may suppress this in its open call
*/
pcm->need_lock = 1;
{
if (mode & SND_PCM_ASYNC) {
/* async handler may lead to a deadlock; suppose no MT */
pcm->lock_enabled = 0;
} else {
/* set lock_enabled field depending on $LIBASOUND_THREAD_SAFE */
static int do_lock_enable = -1; /* uninitialized */