linux-kernel - [Trusty][SRU][PATCH 1/1] ALSA: usb-audio: Prevent printk ratelimiting from spamming kernel log while DEBUG not defined

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Date:	Wed, 18 Jun 2014 13:14:06 -0400
From:	Joseph Salisbury <joseph.salisbury@...onical.com>
To:	kamal.mostafa@...onical.com
Cc:	perex@...ex.cz, tiwai@...e.de, eldad@...refinery.com,
	clemens@...isch.de, tim.gardner@...onical.com,
	stern@...land.harvard.edu, linux@...elenboom.it,
	alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: [Trusty][SRU][PATCH 1/1] ALSA: usb-audio: Prevent printk ratelimiting from spamming kernel log while DEBUG not defined

From: Sander Eikelenboom <linux@...elenboom.it>

BugLink: http://bugs.launchpad.net/bugs/1319457

This (widely used) construction:

if(printk_ratelimit())
	dev_dbg()

Causes the ratelimiting to spam the kernel log with the "callbacks suppressed"
message below, even while the dev_dbg it is supposed to rate limit wouldn't
print anything because DEBUG is not defined for this device.

[  533.803964] retire_playback_urb: 852 callbacks suppressed
[  538.807930] retire_playback_urb: 852 callbacks suppressed
[  543.811897] retire_playback_urb: 852 callbacks suppressed
[  548.815745] retire_playback_urb: 852 callbacks suppressed
[  553.819826] retire_playback_urb: 852 callbacks suppressed

So use dev_dbg_ratelimited() instead of this construction.

Signed-off-by: Sander Eikelenboom <linux@...elenboom.it>
Signed-off-by: Takashi Iwai <tiwai@...e.de>
(backported from commit b7a7723513dc89f83d6df13206df55d4dc26e825)
Signed-off-by: Joseph Salisbury <joseph.salisbury@...onical.com>

---
 sound/usb/pcm.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
index 7bfa7a1..ede4b92 100644
--- a/sound/usb/pcm.c
+++ b/sound/usb/pcm.c
@@ -1487,9 +1487,9 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
 	 * The error should be lower than 2ms since the estimate relies
 	 * on two reads of a counter updated every ms.
 	 */
-	if (printk_ratelimit() &&
-	    abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
-		snd_printk(KERN_DEBUG "delay: estimated %d, actual %d\n",
+	if (abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
+		dev_dbg_ratelimited(&subs->dev->dev,
+			"delay: estimated %d, actual %d\n",
 			est_delay, subs->last_delay);
 
 	if (!subs->running) {
-- 
1.9.1

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