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[209.132.180.67]) by mx.google.com with ESMTP id a11si4975007pgt.124.2019.08.08.17.50.00; Thu, 08 Aug 2019 17:50:16 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405031AbfHIAsp (ORCPT + 99 others); Thu, 8 Aug 2019 20:48:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:34794 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728032AbfHIAsp (ORCPT ); Thu, 8 Aug 2019 20:48:45 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 2F3DA20C01; Fri, 9 Aug 2019 00:48:43 +0000 (UTC) Date: Thu, 8 Aug 2019 20:48:41 -0400 From: Steven Rostedt To: Linus Torvalds Cc: John Ogness , Linux List Kernel Mailing , Peter Zijlstra , Petr Mladek , Sergey Senozhatsky , Greg Kroah-Hartman , Andrea Parri , Thomas Gleixner , Sergey Senozhatsky , Brendan Higgins Subject: Re: [RFC PATCH v4 9/9] printk: use a new ringbuffer implementation Message-ID: <20190808204841.5afcad46@gandalf.local.home> In-Reply-To: References: <20190807222634.1723-1-john.ogness@linutronix.de> <20190807222634.1723-10-john.ogness@linutronix.de> <874l2rclmw.fsf@linutronix.de> <20190808194523.6f83e087@gandalf.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 8 Aug 2019 17:21:09 -0700 Linus Torvalds wrote: > But laptops don't have reset buttons. They have "press the power > button for ten seconds, power turns off. Press it again, and power > comes on" reset sequences. I've never tried, but are you saying that even with the "10 second hold" the laptop's DRAM may still have old data that is accessible? > > They are nasty to debug when they happen on a developer machine (I > should know, I've definitely had them), but when they happen in the > wild they are basically "user just rebooted the machine". End of > story, and no stats or anything like that. Would a best effort 1 page buffer work? Really, with a hard hang we usually only care about the last thing that was printed (we need to add one of those: stop printing after the first WARN_ON is hit, to not lose the initial bug). That way you could have a buffer that is written to constantly but only is the size of one or two pages. It can have a variable in it that gets reset on shutdown. If the system hangs, the next boot could look to see if that page was shutdown cleanly (or never initialized) otherwise, it can read the page or pages into a buffer that can be read from debugfs. A user space tool could read this page and if it detects that it contains data from a crash, notify the user and say "Can you send this to linux-kernel@vger.kernel.org"? Even better if it tells the user the subject and content of the email that should be sent. -- Steve