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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 DE1ECC2D0FA for ; Wed, 13 May 2020 11:04:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C391020740 for ; Wed, 13 May 2020 11:04:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732652AbgEMLEf (ORCPT ); Wed, 13 May 2020 07:04:35 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:57397 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728784AbgEMLEd (ORCPT ); Wed, 13 May 2020 07:04:33 -0400 Received: from fsav108.sakura.ne.jp (fsav108.sakura.ne.jp [27.133.134.235]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 04DB3rMs016231; Wed, 13 May 2020 20:03:53 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav108.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav108.sakura.ne.jp); Wed, 13 May 2020 20:03:53 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav108.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 04DB3qtu016227 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Wed, 13 May 2020 20:03:53 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] printk: Add loglevel for "do not print to consoles". To: Petr Mladek Cc: Sergey Senozhatsky , Michal Hocko , Steven Rostedt , linux-kernel@vger.kernel.org, Dmitry Safonov , Yafang Shao References: <20200427062117.GC486@jagdpanzerIV.localdomain> <4dae86af-1d9a-f5a8-cff6-aa91ec038a79@i-love.sakura.ne.jp> <20200428121828.GP28637@dhcp22.suse.cz> <20200428154532.GU28637@dhcp22.suse.cz> <20200429142106.GG28637@dhcp22.suse.cz> <20200513062652.GM413@jagdpanzerIV.localdomain> <20200513100413.GH17734@linux-b0ei> From: Tetsuo Handa Message-ID: <20564555-7b84-f716-5dcd-978f76ad459a@i-love.sakura.ne.jp> Date: Wed, 13 May 2020 20:03:53 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200513100413.GH17734@linux-b0ei> 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 2020/05/13 19:04, Petr Mladek wrote: >> What is wrong with adding NO_CONSOLES ? > > How does it differ from KERN_DEBUG? The debug messages: > > + can be disabled via sysfs > + might reach console when this loglevel is enabled KERN_NO_CONSOLES is different from KERN_DEBUG in that KERN_NO_CONSOLES itself does not affect userspace daemon's judgement (whether to filter KERN_$LOGLEVEL messages). > What is so special about OOM dump task so that it would deserve such > complications? OOM dump task is special in that it can generate thousands of KERN_INFO messages. If such messages are printed to consoles, it defers solving OOM situation. But setting /proc/sys/vm/oom_dump_tasks to 0 causes such messages being not delivered to userspace daemon for later analysis. Therefore, we can not set /proc/sys/vm/oom_dump_tasks to 0 if we want to save such messages for later analysis. Changing console loglevel (e.g. setting "quiet" kernel command line option) in order to hide such messages also prevents all other KERN_INFO messages from being printed to consoles. Since some KERN_INFO messages are worth printing to consoles while other KERN_INFO messages are worth printing to consoles, controlling with > + loglevel assigned to each message is inevitable. I think that basically only oops (e.g. WARN()/BUG()/panic()) messages worth printing to consoles and the rest messages do not worth printing to consoles. Existing KERN_$LOGLEVEL is too rough-grained.