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Fri, 08 Nov 2019 13:08:38 -0800 (PST) Subject: Re: [PATCH 00/50] Add log level to show_stack() To: Russell King - ARM Linux admin , Dmitry Safonov References: <20191106030542.868541-1-dima@arista.com> <20191106092039.GT4131@hirez.programming.kicks-ass.net> <10db6fa1-5b17-ebe6-09e0-6335e09e4db8@arista.com> <20191106203440.GH3079@worktop.programming.kicks-ass.net> <20191108173045.GY25745@shell.armlinux.org.uk> From: Dmitry Safonov <0x7f454c46@gmail.com> Message-ID: <5a411348-be84-f592-ef2d-ffaec99332bd@gmail.com> Date: Fri, 8 Nov 2019 21:08:30 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20191108173045.GY25745@shell.armlinux.org.uk> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191108_130842_111666_BC36BA18 X-CRM114-Status: GOOD ( 18.89 ) X-BeenThere: linux-snps-arc@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on Synopsys ARC Processors List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Juri Lelli , linux-sh@vger.kernel.org, Catalin Marinas , Ben Segall , Guo Ren , Pavel Machek , Vincent Guittot , Paul Burton , Michael Ellerman , Geert Uytterhoeven , Mel Gorman , Jiri Slaby , Matt Turner , uclinux-h8-devel@lists.sourceforge.jp, Len Brown , linux-pm@vger.kernel.org, linux-um@lists.infradead.org, Thomas Gleixner , Dietmar Eggemann , Richard Henderson , Greg Kroah-Hartman , "Rafael J. Wysocki" , LKML , Ralf Baechle , Paul Mackerras , Andrew Morton , linux-ia64@vger.kernel.org, Tetsuo Handa , James Hogan , "James E.J. Bottomley" , Max Filippov , Vincent Chen , Ingo Molnar , linux-s390@vger.kernel.org, linux-c6x-dev@linux-c6x.org, Yoshinori Sato , linux-hexagon@vger.kernel.org, Helge Deller , "open list:TENSILICA XTENSA PORT \(xtensa\)" , Vasily Gorbik , Aurelien Jacquiot , linux-m68k@lists.linux-m68k.org, Stafford Horne , linux-arm-kernel@lists.infradead.org, Chris Zankel , Tony Luck , Douglas Anderson , Benjamin Herrenschmidt , Heiko Carstens , Will Deacon , Daniel Thompson , Brian Cain , Christian Borntraeger , kgdb-bugreport@lists.sourceforge.net, linux-snps-arc@lists.infradead.org, Fenghua Yu , Borislav Petkov , Jeff Dike , Steven Rostedt , Ivan Kokshaysky , Greentime Hu , Guan Xuetao , linux-parisc@vger.kernel.org, linux-alpha@vger.kernel.org, Ley Foon Tan , "David S. Miller" , Rich Felker , Petr Mladek , Peter Zijlstra , "H. Peter Anvin" , sparclinux@vger.kernel.org, linux-riscv@lists.infradead.org, Anton Ivanov , Jonas Bonn , Richard Weinberger , X86 ML , clang-built-linux@googlegroups.com, Ingo Molnar , Mark Salter , Albert Ou , Stefan Kristiansson , openrisc@lists.librecores.org, Paul Walmsley , Michal Simek , Vineet Gupta , linux-mips@vger.kernel.org, Sergey Senozhatsky , Palmer Dabbelt , Jason Wessel , nios2-dev@lists.rocketboards.org, linuxppc-dev@lists.ozlabs.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-snps-arc" Errors-To: linux-snps-arc-bounces+linux-snps-arc=archiver.kernel.org@lists.infradead.org On 11/8/19 5:30 PM, Russell King - ARM Linux admin wrote: > On Fri, Nov 08, 2019 at 04:28:30PM +0000, Dmitry Safonov wrote: [..] >> >> Well, the use-case for lower log-level is that everything goes into logs >> (/var/log/dmesg or /var/log/messages whatever rsyslog has settting). >> >> That has it's value: >> - after a failure (i.e. panic) messages, those were only signs that >> something goes wrong can be seen in logs which can give ideas what has >> happened. > > No they don't. When the kernel panics, userspace generally stops > running, so rsyslog won't be able to write them to /var/log/messages. > > How, by "kernel panics" I mean a real kernel panic, which probably > isn't what you're talking about there. You are probably talking > about the whole shebang of non-fatal kernel oops, kernel warnings > and the like. If so, I'd ask you to stop confuzzilating terminology. > > If you really want to capture such events, then you need to have the > kernel write the panic to (e.g.) flash - see the mtdoops driver. I was talking about things prior the panic: OOMs, MMC write/read warnings, hung tasks, we also have local patches to produce a warning if the mutex is being held for too long or a task is starving on CPU time by hard/soft irqs (I hope I will design something like that for upstream). I've found those warnings useful to: (a) have an early message when the things are starting going bad. (b) analyze contentions or too large scale for a box or faulty hardware for non-reproducible issues just from logs. We use kexec to save the dmesg ringbuffer content after the panic. Thanks, Dmitry _______________________________________________ linux-snps-arc mailing list linux-snps-arc@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-snps-arc