linux-kernel - [ 059/108] ALSA: usb-audio: Fix scheduling-while-atomic bug in PCM capture stream

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Date:	Wed, 12 Sep 2012 16:28:57 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Greg KH <gregkh@...uxfoundation.org>, Takashi Iwai <tiwai@...e.de>
Subject: [ 059/108] ALSA: usb-audio: Fix scheduling-while-atomic bug in PCM capture stream

From: Greg KH <gregkh@...uxfoundation.org>

3.5-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Takashi Iwai <tiwai@...e.de>

commit e9ba389c5ffc4dd29dfe17e00e48877302111135 upstream.

A PCM capture stream on usb-audio causes a scheduling-while-atomic
BUG, as reported in the bugzilla entry below.  It's because
snd_usb_endpoint_start() is called at first at trigger START for a
capture stream, and this function contains the left-over EP
deactivation codes.  The problem doesn't happen for a playback stream
because the function is called at PCM prepare time, which can sleep.

This patch fixes the BUG by moving the EP deactivation code into the
PCM prepare callback.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=46011
Signed-off-by: Takashi Iwai <tiwai@...e.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 sound/usb/endpoint.c |    4 ----
 sound/usb/pcm.c      |    3 +++
 2 files changed, 3 insertions(+), 4 deletions(-)

--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -821,10 +821,6 @@ int snd_usb_endpoint_start(struct snd_us
 	if (++ep->use_count != 1)
 		return 0;
 
-	/* just to be sure */
-	deactivate_urbs(ep, 0, 1);
-	wait_clear_urbs(ep);
-
 	ep->active_mask = 0;
 	ep->unlink_mask = 0;
 	ep->phase = 0;
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -544,6 +544,9 @@ static int snd_usb_pcm_prepare(struct sn
 	subs->last_frame_number = 0;
 	runtime->delay = 0;
 
+	/* clear the pending deactivation on the target EPs */
+	deactivate_endpoints(subs);
+
 	/* for playback, submit the URBs now; otherwise, the first hwptr_done
 	 * updates for all URBs would happen at the same time when starting */
 	if (subs->direction == SNDRV_PCM_STREAM_PLAYBACK)


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