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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6097EC433EF for ; Wed, 18 May 2022 13:26:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238026AbiERN0p (ORCPT ); Wed, 18 May 2022 09:26:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48656 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237801AbiERNZt (ORCPT ); Wed, 18 May 2022 09:25:49 -0400 Received: from fanzine2.igalia.com (fanzine.igalia.com [178.60.130.6]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C47086B7D6; Wed, 18 May 2022 06:25:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=aBHSQ74cshobrBoDeAcAwH8dbmp4ORux6n0j1EJ9zhs=; b=PbQX6jJxrSTFYuY1QkUAm5HHAj 4zjhUqw9dZUmp+/h7FpyGsMd9T7KC01Lk8wihlfsVt15sYS07bd4AGqx/olI4ChlgEfTgoKgt6ghF u4Ul+3a/u8AC1yN3var2ePdBq3yJ0QNuCnzFCU2AsJ1yN+Ew0qnuNx0AKJJMSgaFsHSKjAS/RJyRX nQBP35ba/Mxst73B+b2bL1GyLemevCz0TIExKe/iFre2S2JyltNIOuuqHTXgx4xNR3AtqS8MDXev4 Htu1aPv+rb/vlxpa70azlfd8R3qZ4EjVERsEcfu9NCpHDF7PwWBcLltMr6Fz/cDtJaPv3zZndTfPs +f+vkTJA==; Received: from 200-161-159-120.dsl.telesp.net.br ([200.161.159.120] helo=[192.168.1.60]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1nrJg7-009yTw-Of; Wed, 18 May 2022 15:25:27 +0200 Message-ID: <5ed2ca7a-5bf3-f101-a1f4-9a320c79f5a0@igalia.com> Date: Wed, 18 May 2022 10:24:39 -0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.0 Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list Content-Language: en-US To: Petr Mladek Cc: Evan Green , David Gow , Julius Werner , Scott Branden , bcm-kernel-feedback-list@broadcom.com, Sebastian Reichel , Linux PM , Florian Fainelli , Andrew Morton , bhe@redhat.com, kexec@lists.infradead.org, LKML , linuxppc-dev@lists.ozlabs.org, linux-alpha@vger.kernel.org, linux-arm Mailing List , linux-edac@vger.kernel.org, linux-hyperv@vger.kernel.org, linux-leds@vger.kernel.org, linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org, linux-remoteproc@vger.kernel.org, linux-s390@vger.kernel.org, linux-tegra@vger.kernel.org, linux-um@lists.infradead.org, linux-xtensa@linux-xtensa.org, netdev@vger.kernel.org, openipmi-developer@lists.sourceforge.net, rcu@vger.kernel.org, sparclinux@vger.kernel.org, xen-devel@lists.xenproject.org, x86@kernel.org, kernel-dev@igalia.com, kernel@gpiccoli.net, halves@canonical.com, fabiomirmar@gmail.com, alejandro.j.jimenez@oracle.com, Andy Shevchenko , Arnd Bergmann , Borislav Petkov , Jonathan Corbet , d.hatayama@jp.fujitsu.com, dave.hansen@linux.intel.com, dyoung@redhat.com, feng.tang@intel.com, Greg Kroah-Hartman , mikelley@microsoft.com, hidehiro.kawai.ez@hitachi.com, jgross@suse.com, john.ogness@linutronix.de, Kees Cook , luto@kernel.org, mhiramat@kernel.org, mingo@redhat.com, paulmck@kernel.org, peterz@infradead.org, rostedt@goodmis.org, senozhatsky@chromium.org, Alan Stern , Thomas Gleixner , vgoyal@redhat.com, vkuznets@redhat.com, Will Deacon , Alexander Gordeev , Andrea Parri , Ard Biesheuvel , Benjamin Herrenschmidt , Brian Norris , Christian Borntraeger , Christophe JAILLET , "David S. Miller" , Dexuan Cui , Doug Berger , Haiyang Zhang , Hari Bathini , Heiko Carstens , Justin Chen , "K. Y. Srinivasan" , Lee Jones , Markus Mayer , Michael Ellerman , Mihai Carabas , Nicholas Piggin , Paul Mackerras , Pavel Machek , Shile Zhang , Stephen Hemminger , Sven Schnelle , Thomas Bogendoerfer , Tianyu Lan , Vasily Gorbik , Wang ShaoBo , Wei Liu , zhenwei pi , Stephen Boyd References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-20-gpiccoli@igalia.com> From: "Guilherme G. Piccoli" In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 18/05/2022 04:33, Petr Mladek wrote: > [...] > Anyway, I would distinguish it the following way. > > + If the notifier is preserving kernel log then it should be ideally > treated as kmsg_dump(). > > + It the notifier is saving another debugging data then it better > fits into the "hypervisor" notifier list. > > Definitely, I agree - it's logical, since we want more info in the logs, and happens some notifiers running in the informational list do that, like ftrace_on_oops for example. > Regarding the reliability. From my POV, any panic notifier enabled > in a generic kernel should be reliable with more than 99,9%. > Otherwise, they should not be in the notifier list at all. > > An exception would be a platform-specific notifier that is > called only on some specific platform and developers maintaining > this platform agree on this. > > The value "99,9%" is arbitrary. I am not sure if it is realistic > even in the other code, for example, console_flush_on_panic() > or emergency_restart(). I just want to point out that the border > should be rather high. Otherwise we would back in the situation > where people would want to disable particular notifiers. > Totally agree, these percentages are just an example, 50% is ridiculous low reliability in my example heheh But some notifiers deep dive in abstraction layers (like regmap or GPIO stuff) and it's hard to determine the probability of a lock issue (take a spinlock already taken inside regmap code and live-lock forever, for example). These are better to run, if possible, later than kdump or even info list. Thanks again for the good analysis Petr! Cheers, Guilherme