Message-ID: <5ed2ca7a-5bf3-f101-a1f4-9a320c79f5a0@igalia.com>
Date:   Wed, 18 May 2022 10:24:39 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Evan Green <evgreen@...omium.org>, David Gow <davidgow@...gle.com>,
        Julius Werner <jwerner@...omium.org>,
        Scott Branden <scott.branden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com,
        Sebastian Reichel <sre@...nel.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, bhe@...hat.com,
        kexec@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org, linux-alpha@...r.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        linux-edac@...r.kernel.org, linux-hyperv@...r.kernel.org,
        linux-leds@...r.kernel.org, linux-mips@...r.kernel.org,
        linux-parisc@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-um@...ts.infradead.org, linux-xtensa@...ux-xtensa.org,
        netdev@...r.kernel.org, openipmi-developer@...ts.sourceforge.net,
        rcu@...r.kernel.org, sparclinux@...r.kernel.org,
        xen-devel@...ts.xenproject.org, x86@...nel.org,
        kernel-dev@...lia.com, kernel@...ccoli.net, halves@...onical.com,
        fabiomirmar@...il.com, alejandro.j.jimenez@...cle.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Jonathan Corbet <corbet@....net>, d.hatayama@...fujitsu.com,
        dave.hansen@...ux.intel.com, dyoung@...hat.com,
        feng.tang@...el.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        mikelley@...rosoft.com, hidehiro.kawai.ez@...achi.com,
        jgross@...e.com, john.ogness@...utronix.de,
        Kees Cook <keescook@...omium.org>, luto@...nel.org,
        mhiramat@...nel.org, mingo@...hat.com, paulmck@...nel.org,
        peterz@...radead.org, rostedt@...dmis.org,
        senozhatsky@...omium.org, Alan Stern <stern@...land.harvard.edu>,
        Thomas Gleixner <tglx@...utronix.de>, vgoyal@...hat.com,
        vkuznets@...hat.com, Will Deacon <will@...nel.org>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Andrea Parri <parri.andrea@...il.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Brian Norris <computersforpeace@...il.com>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        "David S. Miller" <davem@...emloft.net>,
        Dexuan Cui <decui@...rosoft.com>,
        Doug Berger <opendmb@...il.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Justin Chen <justinpopo6@...il.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Lee Jones <lee.jones@...aro.org>,
        Markus Mayer <mmayer@...adcom.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Mihai Carabas <mihai.carabas@...cle.com>,
        Nicholas Piggin <npiggin@...il.com>,
        Paul Mackerras <paulus@...ba.org>, Pavel Machek <pavel@....cz>,
        Shile Zhang <shile.zhang@...ux.alibaba.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sven Schnelle <svens@...ux.ibm.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Wang ShaoBo <bobo.shaobowang@...wei.com>,
        Wei Liu <wei.liu@...nel.org>,
        zhenwei pi <pizhenwei@...edance.com>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH 19/30] panic: Add the panic hypervisor notifier list

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

Powered by blists - more mailing lists