[PATCH] ALSA: usb-audio: Fix implicit sync clearance at stopping stream

[Takashi Iwai]

The recent endpoint management change for implicit feedback mode added
a clearance of ep->sync_sink (formerly ep->sync_slave) pointer at
snd_usb_endpoint_stop() to assure no leftover for the feedback from
the already stopped capture stream.  This turned out to cause a
regression, however, when full-duplex streams were running and only a
capture was stopped.  Because of the above clearance of ep->sync_sink
pointer, no more feedback is done, hence the playback will stall.

This patch fixes the ep->sync_sink clearance to be done only after all
endpoints are released, for addressing the regression.

Reported-and-tested-by: Lucas Endres <jaffa225man at gmail.com>
Fixes: bf6313a0ff76 ("ALSA: usb-audio: Refactor endpoint management")
Cc: <stable at vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 sound/usb/endpoint.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index f4c3d2b38abb..014c43862826 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -1443,11 +1443,11 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep)
 	if (snd_BUG_ON(!atomic_read(&ep->running)))
 		return;
 
-	if (ep->sync_source)
-		WRITE_ONCE(ep->sync_source->sync_sink, NULL);
-
-	if (!atomic_dec_return(&ep->running))
+	if (!atomic_dec_return(&ep->running)) {
+		if (ep->sync_source)
+			WRITE_ONCE(ep->sync_source->sync_sink, NULL);
 		stop_urbs(ep, false);
+	}
 }
 
 /**
-- 
2.26.2