[PATCH 5.12 11/17] ALSA: usb-audio: Fix implicit sync clearance at stopping stream

[Greg Kroah-Hartman]

From: Takashi Iwai <tiwai@xxxxxxx>

commit 988cc17552606be67a956cf8cd6ff504cfc5d643 upstream.

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@xxxxxxxxx>
Fixes: bf6313a0ff76 ("ALSA: usb-audio: Refactor endpoint management")
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210426063349.18601-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 sound/usb/endpoint.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -1442,11 +1442,11 @@ void snd_usb_endpoint_stop(struct snd_us
 	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);
+	}
 }
 
 /**