Revert "ALSA: usb-audio: Fix race at stopping the stream"

This reverts commit 1620094.

The commit was intended to cover the race condition, but it introduced
yet another regression for devices with the implicit feedback, leading
to a kernel panic due to NULL-dereference in an irq context.

As the race condition that was addressed by the commit is very rare
and the regression is much worse, let's revert the commit for rc1, and
fix the issue properly in a later patch.

Fixes: 1620094 ("ALSA: usb-audio: Fix race at stopping the stream")
Reported-by: Ioan-Adrian Ratiu <adi@adirat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: tiwai

sound/usb/endpoint.c

@@ -384,9 +384,6 @@ static void snd_complete_urb(struct urb *urb)
 	if (unlikely(atomic_read(&ep->chip->shutdown)))
 		goto exit_clear;
 
-	if (unlikely(!test_bit(EP_FLAG_RUNNING, &ep->flags)))
-		goto exit_clear;
-
 	if (usb_pipeout(ep->pipe)) {
 		retire_outbound_urb(ep, ctx);
 		/* can be stopped during retire callback */
@@ -537,11 +534,6 @@ static int wait_clear_urbs(struct snd_usb_endpoint *ep)
 			alive, ep->ep_num);
 	clear_bit(EP_FLAG_STOPPING, &ep->flags);
 
-	ep->data_subs = NULL;
-	ep->sync_slave = NULL;
-	ep->retire_data_urb = NULL;
-	ep->prepare_data_urb = NULL;
-
 	return 0;
 }
 
@@ -1028,6 +1020,10 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep)
 
 	if (--ep->use_count == 0) {
 		deactivate_urbs(ep, false);
+		ep->data_subs = NULL;
+		ep->sync_slave = NULL;
+		ep->retire_data_urb = NULL;
+		ep->prepare_data_urb = NULL;
 		set_bit(EP_FLAG_STOPPING, &ep->flags);
 	}
 }