linux-kernel - Re: [PATCH -v2 1/2] ratelimit: Extend to print suppressed messages on release

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Message-ID: <20160701090740.GB4593@pd.tnic>
Date:	Fri, 1 Jul 2016 11:07:40 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, Franck Bui <fbui@...e.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v2 1/2] ratelimit: Extend to print suppressed messages
 on release

On Fri, Jul 01, 2016 at 10:22:47AM +0200, Ingo Molnar wrote:
> > +/* issue num suppressed message on exit */
> > +#define RATELIMIT_MSG_ON_RELEASE	BIT(0)
> 
> So this flag says that we should issue a ratelimit message when it occurs.

This flag says that we should print the ratelimit message when we
release the ratelimit state, i.e., devkmsg_release() for example.

> But here we print the message if the RATELIMIT_MSG_ON_RELEASE bit is zero.
> Is that intentional?

Sure, we want to dump the ratelimited messages only when we release the
ratelimit state.

> Also, while we are changing it, I'd like to suggest a different message - it's 
> talking about 'callbacks' but there's no callback here - we are skipping kernel 
> log messages. So how about:
> 
> 	pr_warn("%s: %d kernel log lines skipped, due to rate-limiting.\n"

Well, I'm not sure: even though the majority of the ratelimit usage is
printing stuff and it has been carved out from printk.c, it still is a
generic facility and you probably want to ratelimit other things too
with it, like polling for something or whatnot.

  [ Whether it is really usable for something else besides ratelimiting
    printk is a whole another question, of course. ]

And ___ratelimit() itself gets a function name as arg so there you
*really* *have* callbacks so %d callbacks suppressed\n" is actually
correct.

I guess I can make the RATELIMIT_MSG_ON_RELEASE message more generic:

static inline void ratelimit_state_exit(struct ratelimit_state *rs)
{
        if (!(rs->flags & RATELIMIT_MSG_ON_RELEASE))
                return;

        if (rs->missed)
                printk(KERN_WARNING "%s: %d output lines suppressed due to ratelimiting\n",
                       current->comm, rs->missed);
}

?

-- 
Regards/Gruss,
    Boris.

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