linux-kernel - Re: [PATCH -v4 1/2] ratelimit: Extend to print suppressed messages on release

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Date:	Thu, 14 Jul 2016 13:29:36 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Franck Bui <fbui@...e.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
Subject: Re: [PATCH -v4 1/2] ratelimit: Extend to print suppressed messages
 on release

On Fri,  8 Jul 2016 11:18:49 +0200 Borislav Petkov <bp@...en8.de> wrote:

> From: Borislav Petkov <bp@...e.de>
> 
> Extend the ratelimiting facility to print the amount of suppressed lines
> when it is being released.

Why?  What's driving this?  What are the benefits to our users?  Are
there any downsides or back-compatibility issues?

I see from the code that this is not actually enabled by default.  The
client code must use ratelimit_set_flags() to select this behaviour,
and the second patch uses this.  Please include all such info in the
changelog.

> Separated from a previous patch by Linus.
> 
> Also, make the ON_RELEASE image not use "callbacks" as it is misleading.

"image"?

I don't understand this sentence.  What's misleading about what?  Much
more detail please.

>
> ...
>
> --- a/lib/ratelimit.c
> +++ b/lib/ratelimit.c
> @@ -46,12 +46,14 @@ int ___ratelimit(struct ratelimit_state *rs, const char *func)
>  		rs->begin = jiffies;
>  
>  	if (time_is_before_jiffies(rs->begin + rs->interval)) {
> -		if (rs->missed)
> -			printk(KERN_WARNING "%s: %d callbacks suppressed\n",
> -				func, rs->missed);
> +		if (rs->missed) {
> +			if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE)) {
> +				pr_warn("%s: %d callbacks suppressed\n", func, rs->missed);
> +				rs->missed = 0;
> +			}
> +		}

hm, what's the difference between an output line being suppressed and a
callback being suppressed?  I think I've forgotten how this code works ;)

>  		rs->begin   = jiffies;
>  		rs->printed = 0;
> -		rs->missed  = 0;
>  	}
>  	if (rs->burst && rs->burst > rs->printed) {
>  		rs->printed++;