[ALSA] usb-audio: properly lock hwptr_done accesses
USB generic driver
Take the substream lock when reading hwptr_done to avoid a race
condition with the updates in the URB callbacks.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 3f7930c..8d4a085 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -815,8 +815,14 @@
*/
static snd_pcm_uframes_t snd_usb_pcm_pointer(snd_pcm_substream_t *substream)
{
- snd_usb_substream_t *subs = (snd_usb_substream_t *)substream->runtime->private_data;
- return subs->hwptr_done;
+ snd_usb_substream_t *subs;
+ snd_pcm_uframes_t hwptr_done;
+
+ subs = (snd_usb_substream_t *)substream->runtime->private_data;
+ spin_lock(&subs->lock);
+ hwptr_done = subs->hwptr_done;
+ spin_unlock(&subs->lock);
+ return hwptr_done;
}