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=-0.8 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 E8271C43382 for ; Fri, 28 Sep 2018 11:01:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 714DF2159D for ; Fri, 28 Sep 2018 11:01:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 714DF2159D 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 S1729397AbeI1RY1 (ORCPT ); Fri, 28 Sep 2018 13:24:27 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:52163 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729093AbeI1RY1 (ORCPT ); Fri, 28 Sep 2018 13:24:27 -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 w8SB1CcA086838; Fri, 28 Sep 2018 20:01:12 +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/530/fsav108.sakura.ne.jp); Fri, 28 Sep 2018 20:01:12 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav108.sakura.ne.jp) Received: from [192.168.1.8] (softbank060157066051.bbtec.net [60.157.66.51]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id w8SB17rb086775 (version=TLSv1.2 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Fri, 28 Sep 2018 20:01:12 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: Re: [PATCH] printk: inject caller information into the body of message To: Sergey Senozhatsky Cc: Sergey Senozhatsky , Petr Mladek , Steven Rostedt , Alexander Potapenko , Dmitriy Vyukov , kbuild test robot , syzkaller , LKML , Linus Torvalds , Andrew Morton References: <20180913071204.GA604@jagdpanzerIV> <20180913122625.6ieyexpcmlc5z2it@pathway.suse.cz> <20180913142802.GB517@tigerII.localdomain> <20180914065728.GA515@jagdpanzerIV> <49d22738-17ad-410a-be0a-d27d76ba9f37@i-love.sakura.ne.jp> <20180914115028.GB20572@tigerII.localdomain> <20180914122217.GA518@tigerII.localdomain> <7dadfa8c-1f69-ae0f-d747-dbbc9f97c2b6@i-love.sakura.ne.jp> <20180928090939.GE1160@jagdpanzerIV> From: Tetsuo Handa Message-ID: <3b378c7d-c613-4a8d-67f8-946fac8ad0b0@i-love.sakura.ne.jp> Date: Fri, 28 Sep 2018 20:01:08 +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: <20180928090939.GE1160@jagdpanzerIV> 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 2018/09/28 18:09, Sergey Senozhatsky wrote: > On (09/24/18 17:11), Tetsuo Handa wrote: >> The reason of using statically preallocated global buffers is that I think >> that it is inconvenient for KERN_CONT users to calculate necessary bytes >> only for avoiding message truncation. The pr_line might be passed to deep >> into the callchain and adjusting buffer size whenever the content's possible >> max length changes is as much painful as changing printk() to accept only >> one "const char *" argument. Even if we guarantee that any context can >> allocate buffer from kernel stack, we cannot guarantee that many concurrent >> printk() won't trigger lockup. Thus, I think that trying to allocate from >> finite static buffers with a fallback to unbuffered printk() upon failure >> is sufficient. > > Yes, this makes sense. At the same time we can keep pr_line buffer > in .bss > > static char buffer[1024]; > static DEFINE_PR_LINE_BUF(..., buffer); > > just like you have already mentioned. But that's going to require a > case-by-case handling; so a big list of printk buffers is a simpler > option. Fallback, tho, can be painful. On a system with 1024 CPUs can > one have more than 16 concurrent cont printks? If the answer is yes, > then we are looking at the same broken cont output as before. I'm OK with making "16" configurable (at kernel configuration and/or at kernel boot like log_buf_len= kernel command line parameter). We could even allow each "struct task_struct" to have corresponding "struct printk_buffer". But if there are such many concurrent callers, the printk() would have already locked up the system to death. ;-)