From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Guilherme G. Piccoli" Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list Date: Wed, 18 May 2022 10:24:39 -0300 Message-ID: <5ed2ca7a-5bf3-f101-a1f4-9a320c79f5a0@igalia.com> References: <20220427224924.592546-1-gpiccoli@igalia.com> <20220427224924.592546-20-gpiccoli@igalia.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To: Subject:MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=eQn7tn+LAXQvaWaOJjs7A40WGwRH89xC92ZZiMNkn9M=; b=GAmZTm+DFJs/I3 1F1WZ+SjC4PwtujnP1urVtJT1fNyudvPuNt5oFKpJWIRgNxT+QEL+9gdcsuysC5VseUL5mZzPkn4a MxFT+jxXslMS/w0RnwvW5R66PNRLAaoiE8PlLIyPVWgQHmlqI1ir3kPKwQhmAvroVrcw41mLEdSmX JxdsdEWmdk3AYDHqtQy5qenVOwtJ1QIGq4iA7u2cXkr6qHLzARUctELJ/KiyUNs6+Vz2ZhrFFEMgf 6iCzXJXF0d6LIyeOOJs6c3RXKRqmCw++XpT4oIYGDM0h0vDuSPflgGNeYlxBOuuDRcV1uG2NRre2w P8qyCTsepmQdjbgKTAWQ==; 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==; Content-Language: en-US In-Reply-To: List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-um" Errors-To: linux-um-bounces+glud-user-mode-linux-devel=m.gmane-mx.org@lists.infradead.org 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-dev 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