linux-kernel - Re: [v3.10.y][v3.11.y][v3.12.y][v3.13.y][v3.14.y][PATCH 1/1][V2] ALSA: usb-audio: Prevent printk ratelimiting from spamming kernel log while DEBUG not defined

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Date:	Thu, 19 Jun 2014 02:52:39 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	Joseph Salisbury <joseph.salisbury@...onical.com>
Cc:	greg@...ah.com, kamal.mostafa@...onical.com,
	luis.henriques@...onical.com, jslaby@...e.cz, clm@...com,
	jbacik@...com, linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [v3.10.y][v3.11.y][v3.12.y][v3.13.y][v3.14.y][PATCH 1/1][V2]
 ALSA: usb-audio: Prevent printk ratelimiting from spamming kernel log while
 DEBUG not defined

On Wed, 2014-06-18 at 14:32 -0400, Joseph Salisbury wrote:
> 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>

It looks like you have combined the commit identified here with the
preceding:

commit a5065eb6da55b226661456e6a7435f605df98111
Author: Tim Gardner <tim.gardner@...onical.com>
Date:   Wed Apr 9 11:30:44 2014 -0600

    ALSA: usb-audio: Suppress repetitive debug messages from retire_playback_urb()

They should not be squashed together like this.

Ben.

> ---
>  sound/usb/pcm.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/sound/usb/pcm.c b/sound/usb/pcm.c
> index ca3256d..ede4b92 100644
> --- a/sound/usb/pcm.c
> +++ b/sound/usb/pcm.c
> @@ -1488,7 +1488,8 @@ static void retire_playback_urb(struct snd_usb_substream *subs,
>  	 * on two reads of a counter updated every ms.
>  	 */
>  	if (abs(est_delay - subs->last_delay) * 1000 > runtime->rate * 2)
> -		snd_printk(KERN_DEBUG "delay: estimated %d, actual %d\n",
> +		dev_dbg_ratelimited(&subs->dev->dev,
> +			"delay: estimated %d, actual %d\n",
>  			est_delay, subs->last_delay);
>  
>  	if (!subs->running) {

-- 
Ben Hutchings
It's easier to fight for one's principles than to live up to them.

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