File 0024-pcm-Disable-locking-in-async-mode.patch of Package alsa.openSUSE_Leap_42.2_Update

From e31a3273df6eb619e35d10bf6a0fc0fded91d559 Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Thu, 9 Feb 2017 17:29:21 +0100
Subject: [PATCH 24/43] 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>
---
 src/pcm/pcm.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/src/pcm/pcm.c
+++ b/src/pcm/pcm.c
@@ -799,6 +799,8 @@ int snd_pcm_async(snd_pcm_t *pcm, int si
 		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_pc
 	 * 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 */