From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00, BUG6152_INVALID_DATE_TZ_ABSURD,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU, HEADER_FROM_DIFFERENT_DOMAINS,INVALID_DATE_TZ_ABSURD,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E745EC433E1 for ; Sat, 18 Jul 2020 14:43:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C042820657 for ; Sat, 18 Jul 2020 14:43:01 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="f4c+55hW"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="HygpJuHR" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728024AbgGROnA (ORCPT ); Sat, 18 Jul 2020 10:43:00 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:47370 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726775AbgGROm7 (ORCPT ); Sat, 18 Jul 2020 10:42:59 -0400 From: John Ogness DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1595083377; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=robvEvPfTGacPLLxfjqEcu14s1gI/E9Po46qbTLNH9U=; b=f4c+55hWWUCG3ELBCMrjgWLE2gsZhHBDVa/JvAlkChgE2cV8SZer9ivxhUTMz53HiVDUyZ vQxr02bZojUUNnLGyj5yDINRDU0AuoxkBkNh7s+x9YqeaEIjN2yyzcBniVqKjA4/H3OTg4 G7bOjhEAIl6yopkDvxGkh7ejY1LoGMNlK6ugEmtdDUS8m71nsZ2QwZGURU3BgbaXEOB/q3 7/vtwA7ecPr7TgEfyDe5XLK2VEvuGD+koJff8GRSuDfroDr8H/OOfxLi7WzgKkT3u5LbQ6 DBBDWq+nXG069WVNdnVRpNTQYgIrpaee5qEjvRY7g5xhjHaOPAagrndMxAAvOA== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1595083377; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=robvEvPfTGacPLLxfjqEcu14s1gI/E9Po46qbTLNH9U=; b=HygpJuHRIGXxBEU/34gMJCGzgTpx8GS6bRIRReV1UJ/TVLQ+RV5oSW53bVibyTWZqwS9DH 7Cls6AERIWr8EPAA== To: Linus Torvalds Cc: Petr Mladek , Sergey Senozhatsky , Sergey Senozhatsky , Steven Rostedt , Greg Kroah-Hartman , Peter Zijlstra , Thomas Gleixner , kexec@lists.infradead.org, Linux Kernel Mailing List Subject: Re: [PATCH 0/4] printk: reimplement LOG_CONT handling In-Reply-To: References: <20200717234818.8622-1-john.ogness@linutronix.de> Date: Sat, 18 Jul 2020 16:48:55 +0206 Message-ID: <87blkcanps.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-07-17, Linus Torvalds wrote: > Make sure you test the case of "fast concurrent readers". The last > time we did things like this, it was a disaster, because a concurrent > reader would see and return the _incomplete_ line, and the next entry > was still being generated on another CPU. > > The reader would then decide to return that incomplete line, because > it had something. > > And while in theory this could then be handled properly in user space, > in practice it wasn't. So you'd see a lot of logging tools that would > then report all those continuations as separate log events. > > Which is the whole point of LOG_CONT - for that *not* to happen. I expect this is handled correctly since the reader is not given any parts until a full line is ready, but I will put more focus on testing this to make sure. Thanks for the regression and testing tips. > So this is just a heads-up that I will not pull something that breaks > LOG_CONT because it thinks "user space can handle it". No. User space > does not handle it, and we need to handle it for the user. Understood. Petr and Sergey are also strict about this. We are making a serious effort to avoid breaking things for userspace. John Ogness From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from galois.linutronix.de ([2a0a:51c0:0:12e:550::1]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1jwo3I-0004Rr-6F for kexec@lists.infradead.org; Sat, 18 Jul 2020 14:43:01 +0000 From: John Ogness Subject: Re: [PATCH 0/4] printk: reimplement LOG_CONT handling In-Reply-To: References: <20200717234818.8622-1-john.ogness@linutronix.de> Date: Sat, 18 Jul 2020 16:48:55 +0206 Message-ID: <87blkcanps.fsf@jogness.linutronix.de> MIME-Version: 1.0 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Linus Torvalds Cc: Petr Mladek , Sergey Senozhatsky , Peter Zijlstra , Greg Kroah-Hartman , kexec@lists.infradead.org, Linux Kernel Mailing List , Steven Rostedt , Sergey Senozhatsky , Thomas Gleixner On 2020-07-17, Linus Torvalds wrote: > Make sure you test the case of "fast concurrent readers". The last > time we did things like this, it was a disaster, because a concurrent > reader would see and return the _incomplete_ line, and the next entry > was still being generated on another CPU. > > The reader would then decide to return that incomplete line, because > it had something. > > And while in theory this could then be handled properly in user space, > in practice it wasn't. So you'd see a lot of logging tools that would > then report all those continuations as separate log events. > > Which is the whole point of LOG_CONT - for that *not* to happen. I expect this is handled correctly since the reader is not given any parts until a full line is ready, but I will put more focus on testing this to make sure. Thanks for the regression and testing tips. > So this is just a heads-up that I will not pull something that breaks > LOG_CONT because it thinks "user space can handle it". No. User space > does not handle it, and we need to handle it for the user. Understood. Petr and Sergey are also strict about this. We are making a serious effort to avoid breaking things for userspace. John Ogness _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec