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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 52EFFC32789 for ; Thu, 8 Nov 2018 11:46:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2181820892 for ; Thu, 8 Nov 2018 11:46:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2181820892 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=i-love.sakura.ne.jp Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726722AbeKHVVh (ORCPT ); Thu, 8 Nov 2018 16:21:37 -0500 Received: from www262.sakura.ne.jp ([202.181.97.72]:18043 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726252AbeKHVVh (ORCPT ); Thu, 8 Nov 2018 16:21:37 -0500 Received: from fsav405.sakura.ne.jp (fsav405.sakura.ne.jp [133.242.250.104]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id wA8BkS7h021813; Thu, 8 Nov 2018 20:46:29 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav405.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav405.sakura.ne.jp); Thu, 08 Nov 2018 20:46:28 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav405.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157065137.bbtec.net [60.157.65.137]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id wA8BkS66021803 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Thu, 8 Nov 2018 20:46:28 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH v6 1/3] printk: Add line-buffered printk() API. To: Petr Mladek , Sergey Senozhatsky Cc: Sergey Senozhatsky , Dmitriy Vyukov , Steven Rostedt , Alexander Potapenko , Fengguang Wu , Josh Poimboeuf , LKML , Linus Torvalds , Andrew Morton , linux-mm@kvack.org, Ingo Molnar , Peter Zijlstra , Will Deacon References: <1541165517-3557-1-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp> <20181106143502.GA32748@tigerII.localdomain> <20181107102154.pobr7yrl5il76be6@pathway.suse.cz> <20181108022138.GA2343@jagdpanzerIV> <20181108112443.huqkju4uwrenvtnu@pathway.suse.cz> From: Tetsuo Handa Message-ID: Date: Thu, 8 Nov 2018 20:46:28 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20181108112443.huqkju4uwrenvtnu@pathway.suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018/11/08 20:24, Petr Mladek wrote: >> Let's have one more look at what we will fix and what we will break. >> >> 'cont' has premature flushes. >> >> Why is it good. >> It preserves the correct order of events. >> >> pr_cont("calling foo->init()...."); >> foo->init() >> printk("Can't allocate buffer\n"); // premature flush >> pr_cont("...blah\h"); >> >> Will end up in the logbuf as: >> [12345.123] calling foo->init().... >> [12345.124] Can't allocate buffer >> [12345.125] ...blah >> >> Where buffered printk will endup as: >> [12345.123] Can't allocate buffer >> [12345.124] calling foo->init().......blah > > We will always have this problem with API using explicit buffers. > What do you suggest instead, please? > > I am afraid that we are running in cycles. The other serious > alternative was having per-process and per-context buffers > but it was rejected several times. Is it possible to identify all locations which should use their own printk() buffers (e.g. interrupt handlers, oops handlers) ? If yes, automatically switching printk() buffers (like memalloc_nofs_save()/ memalloc_nofs_restore()) will be easiest and least error prone.