From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753034AbeEKMlM (ORCPT ); Fri, 11 May 2018 08:41:12 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:55946 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752981AbeEKMlH (ORCPT ); Fri, 11 May 2018 08:41:07 -0400 X-Google-Smtp-Source: AB8JxZqA3Ln8hmbz1a/RBHpy4VO2445h7bZF16rmLsITNXFzCK50GkItYY22NG21G7tONE9ERf4Jcw== Message-ID: <1526042463.28243.21.camel@arista.com> Subject: Re: [PATCH 1/2] random: Omit double-printing ratelimit messages From: Dmitry Safonov To: "Theodore Y. Ts'o" Cc: linux-kernel@vger.kernel.org, 0x7f454c46@gmail.com, Arnd Bergmann Date: Fri, 11 May 2018 13:41:03 +0100 In-Reply-To: <20180511035150.GJ8335@thunk.org> References: <20180510125211.12583-1-dima@arista.com> <20180510125211.12583-2-dima@arista.com> <20180510181901.GG8335@thunk.org> <1525977460.28243.2.camel@arista.com> <20180510194041.GH8335@thunk.org> <1525981807.28243.9.camel@arista.com> <20180511035150.GJ8335@thunk.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.24.6 (3.24.6-1.fc26) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2018-05-10 at 23:51 -0400, Theodore Y. Ts'o wrote: > 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. Yes, if the initialization time of driver is lesser than a second. If it's 1.1 sec - you'll have prints from ___ratelimit() and from your driver too. And they differ in format. > 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. So, there is this flag, AFAICS, which perfectly fits your purpose RATELIMIT_MSG_ON_RELEASE which will omit printing how many messages were suppressed every interval of ___ratelimit(). And that will allow you to print total in the end. > It is not a double-count. If we didn't do that, those suppressed > warnings would never be mentioned by the kernel. Yeah, but what you print is not total sum, it's since the last interval because without mentioned flag ___ratelimit() will flush missed counter and print "suppressed" message. They might even double if say other proccess has called get_random_bytes() got to ___ratelimit() and got preempted. This thread finishes initializing random driver and prints this not-proper-sum statistics, and when the code flow is back in the first context, it will print statistics again from ___ratelimit() function. -- Thanks, Dmitry