[alsa-devel] [PATCH] pcm: direct: Fix deadlock in poll_descriptors

[Takashi Iwai]

The recent change in PCM direct plugins to check XRUN in
poll_descriptors callback caused a regression; as consequence, the
whole playback hangs up.

The culprit is a mutex dead lock by the call in snd_pcm_state() inside
the new snd_pcm_direct_poll_descriptors().  The poll_descriptors code
path is protected with pcm mutex, thus an unlocked version
(__snd_pcm_state()) has to be used inside the callback instead.

Fixes: 789ee39727a1 ("pcm: direct: check state before enter poll on timer")
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 src/pcm/pcm_direct.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/pcm/pcm_direct.c b/src/pcm/pcm_direct.c
index f4d7c3f2f284..e4bef7860d01 100644
--- a/src/pcm/pcm_direct.c
+++ b/src/pcm/pcm_direct.c
@@ -676,7 +676,8 @@ int snd_pcm_direct_poll_descriptors(snd_pcm_t *pcm, struct pollfd *pfds,
 	}
 
 	/* this will also evaluate slave state and enter xrun if necessary */
-	switch (snd_pcm_state(pcm)) {
+	/* using __snd_pcm_state() since this function is called inside lock */
+	switch (__snd_pcm_state(pcm)) {
 	case SND_PCM_STATE_XRUN:
 		return -EPIPE;
 	default:
-- 
2.11.0