commit daa150ef7d437d17973210f47a1c58623415df94
author Clemens Ladisch <clemens@ladisch.de> Mon Aug 15 08:25:50 2005 +0200
committer Jaroslav Kysela <perex@suse.cz> Tue Aug 30 08:45:50 2005 +0200
tree e41056adf7f00cad4681051d4b7d6b524ea8a68f
parent 9624ea812c7afd2e403c56366cadddb9ecfb88c6

[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>

sound/usb/usbaudio.c

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;
 }