pcm: Disable locking in async mode

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>

diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c
index c136d55793207c41c29a559eebb25811e1762e28..493e9039b5082df62d39ad192f2a504de3b72001 100644 (file)
--- 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 */