From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx176.postini.com [74.125.245.176]) by kanga.kvack.org (Postfix) with SMTP id 539A16B004A for ; Tue, 13 Mar 2012 04:32:36 -0400 (EDT) Message-ID: <4F5F0620.2020404@codeaurora.org> Date: Tue, 13 Mar 2012 01:32:32 -0700 From: Stephen Boyd MIME-Version: 1.0 Subject: Re: [PATCH 0/5] Persist printk buffer across reboots. References: <1331617001-20906-1-git-send-email-apenwarr@gmail.com> In-Reply-To: <1331617001-20906-1-git-send-email-apenwarr@gmail.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Avery Pennarun Cc: Andrew Morton , Josh Triplett , "Paul E. McKenney" , Ingo Molnar , "David S. Miller" , Peter Zijlstra , "Fabio M. Di Nitto" , Johannes Weiner , Olaf Hering , Paul Gortmaker , Tejun Heo , "H. Peter Anvin" , Yinghai LU , linux-kernel@vger.kernel.org, linux-mm@kvack.org On 3/12/2012 10:36 PM, Avery Pennarun wrote: > The last patch in this series implements a new CONFIG_PRINTK_PERSIST option > that, when enabled, puts the printk buffer in a well-defined memory location > so that we can keep appending to it after a reboot. The upshot is that, > even after a kernel panic or non-panic hard lockup, on the next boot > userspace will be able to grab the kernel messages leading up to it. It > could then upload the messages to a server (for example) to keep crash > statistics. > > The preceding patches in the series are mostly just things I fixed up while > working on that patch. > > Some notes: > > - I'm not totally sure of the locking or portability issues when calling > memblock or bootmem. This all happens really early, and I *think* > interrupts are still disabled at that time, so it's probably okay. > > - Tested this version on x86 (kvm) and it works with soft reboot (ie. reboot > -f). Since some BIOSes wipe the memory during boot, you might not have > any luck. It should be great on many embedded systems, though, including > the MIPS system I've tested a variant of this patch on. (Our MIPS build > is based on a slightly older kernel so it's not 100% the same, but I think > this should behave identically.) > > - The way we choose a well-defined memory location is slightly suspicious > (we just count down from the top of the address space) but I've tested it > pretty carefully, and it seems to be okay. > > - In printk.c with CONFIG_PRINTK_PERSIST set, we're #defining words like > log_end. It might be cleaner to replace all instances of log_end with > LOG_END to make this more clear. This is also the reason the struct > logbits members start with _: because otherwise they conflict with the > macro. Suggestions welcome. Android has something similar called ram_console (see staging/android/ram_console.c). The console is dumped to a ram buffer that is reserved very early in platform setup code. Then when the phone reboots you can cat /proc/last_kmsg to get the previous kernel message for debugging. Can you use that code? -- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org