[PATCH 3.16 129/136] ALSA: usb-audio: not submit urb for stopped endpoint

[Ben Hutchings]

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Henry Lin <henryl@xxxxxxxxxx>

commit 528699317dd6dc722dccc11b68800cf945109390 upstream.

While output urb's snd_complete_urb() is executing, calling
prepare_outbound_urb() may cause endpoint stopped before
prepare_outbound_urb() returns and result in next urb submitted
to stopped endpoint. usb-audio driver cannot re-use it afterwards as
the urb is still hold by usb stack.

This change checks EP_FLAG_RUNNING flag after prepare_outbound_urb() again
to let snd_complete_urb() know the endpoint already stopped and does not
submit next urb. Below kind of error will be fixed:

[  213.153103] usb 1-2: timeout: still 1 active urbs on EP #1
[  213.164121] usb 1-2: cannot submit urb 0, error -16: unknown error

Signed-off-by: Henry Lin <henryl@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20191113021420.13377-1-henryl@xxxxxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 sound/usb/endpoint.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -377,6 +377,9 @@ static void snd_complete_urb(struct urb
 		}
 
 		prepare_outbound_urb(ep, ctx);
+		/* can be stopped during prepare callback */
+		if (unlikely(!test_bit(EP_FLAG_RUNNING, &ep->flags)))
+			goto exit_clear;
 	} else {
 		retire_inbound_urb(ep, ctx);
 		/* can be stopped during retire callback */