Commit 43b81e84 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: usb-audio: Use atomic_t for endpoint use_count 



The endpoint objects may be started/stopped concurrently by different
substreams in the case of implicit feedback mode, while the current
code handles the reference counter without any protection.

This patch changes the refcount to atomic_t for avoiding the
inconsistency.  We need no reference_t here as the refcount goes only
up to 2.

Also the name "use_count" is renamed to "running" since this is about
actually the running status, not the open refcount.

Tested-by: default avatarKeith Milner <kamilner@superlative.org>
Tested-by: default avatarDylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-29-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent cab941b7

sound/usb/card.h

+1 −1
Original line number Diff line number Diff line
@@ -60,7 +60,7 @@ struct snd_usb_endpoint { 
	struct snd_usb_audio *chip;



	int opened;		/* open refcount; protect with chip->mutex */

	int use_count;

	atomic_t running;	/* running status */

	int ep_num;		/* the referenced endpoint number */

	int type;		/* SND_USB_ENDPOINT_TYPE_* */

	unsigned long flags;

sound/usb/endpoint.c

+14 −12
Original line number Diff line number Diff line
@@ -1234,7 +1234,7 @@ int snd_usb_endpoint_configure(struct snd_usb_audio *chip, 
 *

 * @ep: the endpoint to start

 *

 * A call to this function will increment the use count of the endpoint.

 * A call to this function will increment the running count of the endpoint.

 * In case it is not already running, the URBs for this endpoint will be

 * submitted. Otherwise, this function does nothing.

 *
@@ -1253,11 +1253,12 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep) 
	if (ep->sync_master)

		WRITE_ONCE(ep->sync_master->sync_slave, ep);



	usb_audio_dbg(ep->chip, "Starting %s EP 0x%x (count %d)\n",

		      ep_type_name(ep->type), ep->ep_num, ep->use_count);

	usb_audio_dbg(ep->chip, "Starting %s EP 0x%x (running %d)\n",

		      ep_type_name(ep->type), ep->ep_num,

		      atomic_read(&ep->running));



	/* already running? */

	if (++ep->use_count != 1)

	if (atomic_inc_return(&ep->running) != 1)

		return 0;



	/* just to be sure */
@@ -1319,7 +1320,7 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep) 
	if (ep->sync_master)

		WRITE_ONCE(ep->sync_master->sync_slave, NULL);

	clear_bit(EP_FLAG_RUNNING, &ep->flags);

	ep->use_count--;

	atomic_dec(&ep->running);

	deactivate_urbs(ep, false);

	return -EPIPE;

}
@@ -1329,7 +1330,7 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep) 
 *

 * @ep: the endpoint to stop (may be NULL)

 *

 * A call to this function will decrement the use count of the endpoint.

 * A call to this function will decrement the running count of the endpoint.

 * In case the last user has requested the endpoint stop, the URBs will

 * actually be deactivated.

 *
@@ -1343,16 +1344,17 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep) 
	if (!ep)

		return;



	usb_audio_dbg(ep->chip, "Stopping %s EP 0x%x (count %d)\n",

		      ep_type_name(ep->type), ep->ep_num, ep->use_count);

	usb_audio_dbg(ep->chip, "Stopping %s EP 0x%x (running %d)\n",

		      ep_type_name(ep->type), ep->ep_num,

		      atomic_read(&ep->running));



	if (snd_BUG_ON(ep->use_count == 0))

	if (snd_BUG_ON(!atomic_read(&ep->running)))

		return;



	if (ep->sync_master)

		WRITE_ONCE(ep->sync_master->sync_slave, NULL);



	if (--ep->use_count == 0) {

	if (!atomic_dec_return(&ep->running)) {

		deactivate_urbs(ep, false);

		set_bit(EP_FLAG_STOPPING, &ep->flags);

	}
@@ -1363,7 +1365,7 @@ void snd_usb_endpoint_stop(struct snd_usb_endpoint *ep) 
 *

 * @ep: the endpoint to release

 *

 * This function does not care for the endpoint's use count but will tear

 * This function does not care for the endpoint's running count but will tear

 * down all the streaming URBs immediately.

 */

void snd_usb_endpoint_release(struct snd_usb_endpoint *ep)
@@ -1410,7 +1412,7 @@ static void snd_usb_handle_sync_urb(struct snd_usb_endpoint *ep, 
	 * will take care of them later.

	 */

	if (snd_usb_endpoint_implicit_feedback_sink(ep) &&

	    ep->use_count != 0) {

	    atomic_read(&ep->running)) {



		/* implicit feedback case */

		int i, bytes = 0;