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,URIBL_BLOCKED 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 85B6DC43381 for ; Fri, 22 Mar 2019 00:48:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5A92F21902 for ; Fri, 22 Mar 2019 00:48:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727501AbfCVAsJ (ORCPT ); Thu, 21 Mar 2019 20:48:09 -0400 Received: from ozlabs.org ([203.11.71.1]:42181 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726460AbfCVAsI (ORCPT ); Thu, 21 Mar 2019 20:48:08 -0400 Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 44QQ4N57fxz9sP2; Fri, 22 Mar 2019 11:48:04 +1100 (AEDT) From: Michael Ellerman To: Petr Mladek Cc: Tetsuo Handa , Sergey Senozhatsky , Dmitry Vyukov , Sergey Senozhatsky , Steven Rostedt , Linus Torvalds , Andrew Morton , LKML , syzkaller Subject: Re: [PATCH] printk: Add caller information to printk() output. In-Reply-To: <20190321102013.yxs4v4pcrq44jktm@pathway.suse.cz> References: <20181204152724.ypk44mi4a56nrud4@pathway.suse.cz> <459018db-763b-9520-ead2-2c0d5975fbf3@i-love.sakura.ne.jp> <20181210130930.bas4fozjhe3dc5nu@pathway.suse.cz> <20181213121847.mwlr2vyv6qzclhk6@pathway.suse.cz> <20181213124255.GB3053@tigerII.localdomain> <20181217145452.3kev4rmo2l5lt2qy@pathway.suse.cz> <93f19e57-5051-c67d-9af4-b17624062d44@i-love.sakura.ne.jp> <871s312aqe.fsf@concordia.ellerman.id.au> <20190321102013.yxs4v4pcrq44jktm@pathway.suse.cz> Date: Fri, 22 Mar 2019 11:48:04 +1100 Message-ID: <877ecrka4b.fsf@concordia.ellerman.id.au> 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 Petr Mladek writes: > On Thu 2019-03-21 13:59:53, Michael Ellerman wrote: >> Tetsuo Handa writes: >> ... >> > From 91f85d2bd494df2f73c605d8b4747e8cc0a61ae2 Mon Sep 17 00:00:00 2001 >> > From: Tetsuo Handa >> > Date: Tue, 18 Dec 2018 05:53:04 +0900 >> > Subject: [PATCH] printk: Add caller information to printk() output. >> > >> > Sometimes we want to print a series of printk() messages to consoles >> > without being disturbed by concurrent printk() from interrupts and/or >> > other threads. But we can't enforce printk() callers to use their local >> > buffers because we need to ask them to make too much changes. Also, even >> > buffering up to one line inside printk() might cause failing to emit >> > an important clue under critical situation. >> > >> > Therefore, instead of trying to help buffering, let's try to help >> > reconstructing messages by saving caller information as of calling >> > log_store() and adding it as "[T$thread_id]" or "[C$processor_id]" >> > upon printing to consoles. >> > >> > Some examples for console output: >> > >> > [ 1.222773][ T1] x86: Booting SMP configuration: >> > [ 2.779635][ T1] pci 0000:00:01.0: PCI bridge to [bus 01] >> > [ 5.069193][ T268] Fusion MPT base driver 3.04.20 >> > [ 9.316504][ C2] random: fast init done >> > [ 13.413336][ T3355] Initialized host personality >> > >> > Some examples for /dev/kmsg output: >> > >> > 6,496,1222773,-,caller=T1;x86: Booting SMP configuration: >> > 6,968,2779635,-,caller=T1;pci 0000:00:01.0: PCI bridge to [bus 01] >> > SUBSYSTEM=pci >> > DEVICE=+pci:0000:00:01.0 >> > 6,1353,5069193,-,caller=T268;Fusion MPT base driver 3.04.20 >> > 5,1526,9316504,-,caller=C2;random: fast init done >> > 6,1575,13413336,-,caller=T3355;Initialized host personality >> > >> > Note that this patch changes max length of messages which can be printed >> > by printk() or written to /dev/kmsg interface from 992 bytes to 976 bytes, >> > based on an assumption that userspace won't try to write messages hitting >> > that border line to /dev/kmsg interface. >> >> Do you have any plans to update dmesg or other userspace tools to show >> the caller information? > > dmesg already works via the syslog interface, try dmesg -S. Oh nice, thanks. > The current implementation does not pass the information into > the /dev/kmsg interface. It has the following format: > > ",,,[,additional_values, ... ];\n" > > It would be possible to add it as an additional value. To be hones > I am not sure how they are handled by userspace tools. OK, yeah I guess there's the potential for a backward compatibility can of worms there. I'm happy with dmesg -S :) cheers