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Date: Tue, 15 Feb 2022 17:14:51 +0100 From: Petr Mladek <pmladek@...e.com> To: "Guilherme G. Piccoli" <gpiccoli@...lia.com> Cc: linux-kernel@...r.kernel.org, bhe@...hat.com, akpm@...ux-foundation.org, anton@...msg.org, ccross@...roid.com, dyoung@...hat.com, feng.tang@...el.com, john.ogness@...utronix.de, keescook@...omium.org, kernel@...ccoli.net, kexec@...ts.infradead.org, rostedt@...dmis.org, senozhatsky@...omium.org, tony.luck@...el.com, vgoyal@...hat.com Subject: Re: [PATCH V6] panic: Move panic_print before kmsg dumpers On Mon 2022-02-14 11:13:09, Guilherme G. Piccoli wrote: > The panic_print setting allows users to collect more information in a > panic event, like memory stats, tasks, CPUs backtraces, etc. > This is an interesting debug mechanism, but currently the print event > happens *after* kmsg_dump(), meaning that pstore, for example, cannot > collect a dmesg with the panic_print extra information. > > This patch changes that in 2 steps: > > (a) The panic_print setting allows to replay the existing kernel log > buffer to the console (bit 5), besides the extra information dump. > This functionality makes sense only at the end of the panic() function. > So, we hereby allow to distinguish the two situations by a new boolean > parameter in the function panic_print_sys_info(). > > (b) With the above change, we can safely call panic_print_sys_info() > before kmsg_dump(), allowing to dump the extra information when using > pstore or other kmsg dumpers. > > The additional messages from panic_print could overwrite the oldest > messages when the buffer is full. The only reasonable solution is to > use a large enough log buffer, hence we added an advice into the kernel > parameters documentation about that. > > Cc: Feng Tang <feng.tang@...el.com> > Cc: Petr Mladek <pmladek@...e.com> > Acked-by: Baoquan He <bhe@...hat.com> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@...lia.com> Makes sense and looks good to me. Reviewed-by: Petr Mladek <pmladek@...e.com> Best Regards, Petr
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