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 --- src/pcm/pcm.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c index c136d5579320..493e9039b508 100644 --- a/src/pcm/pcm.c +++ b/src/pcm/pcm.c @@ -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 */