From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758041Ab2EKBYH (ORCPT ); Thu, 10 May 2012 21:24:07 -0400 Received: from mail-wg0-f42.google.com ([74.125.82.42]:53311 "EHLO mail-wg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757301Ab2EKBYE (ORCPT ); Thu, 10 May 2012 21:24:04 -0400 Message-ID: <1336699411.835.5.camel@mop> Subject: Re: [PATCH RESEND 1/3] printk: convert byte-buffer to variable-length record buffer From: Kay Sievers To: Linus Torvalds Cc: Joe Perches , "Ted Ts'o" , Ingo Molnar , Jonathan Corbet , Sasha Levin , Greg Kroah-Hartmann , linux-kernel@vger.kernel.org Date: Fri, 11 May 2012 03:23:31 +0200 In-Reply-To: <1336696707.947.56.camel@mop> References: <20120509070710.GA29981@gmail.com> <1336611278.728.9.camel@mop> <1336667984.947.24.camel@mop> <1336676986.947.47.camel@mop> <20120510201409.GA6467@thunk.org> <1336682226.29763.2.camel@joe2Laptop> <1336682772.29763.6.camel@joe2Laptop> <1336696707.947.56.camel@mop> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.1 (3.4.1-2.fc17) Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2012-05-11 at 02:38 +0200, Kay Sievers wrote: > On Thu, May 10, 2012 at 10:52 PM, Linus Torvalds wrote: > > > The change to verify that 'current' matches the previous printout is > > so far the *only* sane semantic change I've seen in this thread. > > Everything else has been pure garbage. > > Ok, let's continue with sane things then. :) > > Here is a stupid kernel module which creates 3 racy printk() loops, 2 of > them do continuation, one does an atomic print. The continuation one > prints one char per printk. > http://people.freedesktop.org/~kay/printk-race/printk-race.c > > The lines all try to look like: > (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) > (CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC) > (XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX) > > Every loop has it's own uppercase character. The line enclosed in '()'. > 'A' is the atomic one, the cont ones are 'C' and 'X'. Having only one continuation user racing against an atomic printk user looks like this: Current kernel: [ 54.062900] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.068200] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.071698] (CC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.074103] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.076052] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.078116] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.080096] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.082060] CC(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 54.086121] C(AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) http://people.freedesktop.org/~kay/printk-race/printk-out-before-2.txt Record buffer, with cont buffer owner: [ 33.431129] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.435112] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.439131] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.441820] (CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC) [ 33.445292] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.450131] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.453127] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.456084] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.459143] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.462161] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) [ 33.465165] (AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA) http://people.freedesktop.org/~kay/printk-race/printk-out-after-2.txt Kay