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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: Keith Milner <kamilner@superlative.org>
Tested-by: Dylan Robinson <dylan_robinson@motu.com>
Link: https://lore.kernel.org/r/20201123085347.19667-29-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2020-11-23 09:53:34 +01:00
parent cab941b7e5
commit 43b81e8406
2 changed files with 15 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sound/usb/card.h
View File

@ -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;

26
sound/usb/endpoint.c
View File

@ -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;