linux-kernel - Re: [PATCH 1/2] random: Omit double-printing ratelimit messages

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Message-ID: <20180511035150.GJ8335@thunk.org>
Date:   Thu, 10 May 2018 23:51:50 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Dmitry Safonov <dima@...sta.com>
Cc:     linux-kernel@...r.kernel.org, 0x7f454c46@...il.com,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/2] random: Omit double-printing ratelimit messages

On Thu, May 10, 2018 at 08:50:07PM +0100, Dmitry Safonov wrote:
> random uses __ratelimit() which calls ___ratelimit() with a function
> name. Depending on !RATELIMIT_MSG_ON_RELEASE it prints how many
> messages were suppressed every ratelimit interval (1 second for random)
> and flushes ratelimit_state::missed:

So the thing about the ratelimit system is that if you have a burst of
1,000,000 within the one second burst window, and then nothing ever
again, you will never see a message accounting for those 1,000,000
"callbacks" (which is a terrible wording; it just confuses people).

If you have a burst of 1,000,000 calls to ratelimit, and then a month
goes by, and *then* a single call to __ratelimit is called by printk,
only *the* does the message about the suppressed "callback" get
printed.

So in the case of the random driver, once the random driver is fully
intialized, there will never be a call to __ratelimit() for the
urandom ratelimit structures, so we manually print out the final
number of suppressed message so there is proper accounting for them.

It is not a double-count.  If we didn't do that, those suppressed
warnings would never be mentioned by the kernel.

Cheers,

						- Ted