From: Clemens Ladisch <clemens@ladisch.de>
Date: Mon, 15 Aug 2005 06:25:50 +0000 (+0200)
Subject: [ALSA] usb-audio: properly lock hwptr_done accesses
X-Git-Tag: v2.6.14-rc1~1029^2~39
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=daa150ef7d437d17973210f47a1c58623415df94;p=linux-2.6

[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 3f7930c0b6..8d4a085f64 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -815,8 +815,14 @@ static int wait_clear_urbs(snd_usb_substream_t *subs)
  */
 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;
 }