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Date: Tue, 16 Nov 2021 07:37:29 +0100
From: Christophe Leroy <>
To: Steven Rostedt <>,
 Lukas Bulwahn <>
Cc: Alexander Popov <>,
 Linus Torvalds <>,
 Jonathan Corbet <>, Paul McKenney <>,
 Andrew Morton <>,
 Thomas Gleixner <>, Peter Zijlstra <>,
 Joerg Roedel <>, Maciej Rozycki <>,
 Muchun Song <>,
 Viresh Kumar <>, Robin Murphy <>,
 Randy Dunlap <>, Lu Baolu <>,
 Petr Mladek <>, Kees Cook <>,
 Luis Chamberlain <>, Wei Liu <>,
 John Ogness <>,
 Andy Shevchenko <>,
 Alexey Kardashevskiy <>, Jann Horn <>,
 Greg Kroah-Hartman <>,
 Mark Rutland <>, Andy Lutomirski <>,
 Dave Hansen <>, Will Deacon <>,
 Ard Biesheuvel <>, Laura Abbott <>,
 David S Miller <>, Borislav Petkov <>,
 Arnd Bergmann <>, Andrew Scull <>,
 Marc Zyngier <>, Jessica Yu <>,
 Iurii Zaikin <>,
 Rasmus Villemoes <>, Wang Qing <>,
 Mel Gorman <>,
 Mauro Carvalho Chehab <>,
 Andrew Klychkov <>,
 Mathieu Chouquet-Stringer <>,
 Daniel Borkmann <>, Stephen Kitt <>,
 Stephen Boyd <>,
 Thomas Bogendoerfer <>,
 Mike Rapoport <>, Bjorn Andersson
 Kernel Hardening <>,,
 "open list:DOCUMENTATION" <>,
 linux-arch <>,
 Linux Kernel Mailing List <>,
 linux-fsdevel <>,,,,, Shuah Khan <>
Subject: Re: [PATCH v2 0/2] Introduce the pkill_on_warn parameter

Le 15/11/2021 à 17:06, Steven Rostedt a écrit :
> On Mon, 15 Nov 2021 14:59:57 +0100
> Lukas Bulwahn <> wrote:
>> 1. Allow a reasonably configured kernel to boot and run with
>> panic_on_warn set. Warnings should only be raised when something is
>> not configured as the developers expect it or the kernel is put into a
>> state that generally is _unexpected_ and has been exposed little to
>> the critical thought of the developer, to testing efforts and use in
>> other systems in the wild. Warnings should not be used for something
>> informative, which still allows the kernel to continue running in a
>> proper way in a generally expected environment. Up to my knowledge,
>> there are some kernels in production that run with panic_on_warn; so,
>> IMHO, this requirement is generally accepted (we might of course
> To me, WARN*() is the same as BUG*(). If it gets hit, it's a bug in the
> kernel and needs to be fixed. I have several WARN*() calls in my code, and
> it's all because the algorithms used is expected to prevent the condition
> in the warning from happening. If the warning triggers, it means either that
> the algorithm is wrong or my assumption about the algorithm is wrong. In
> either case, the kernel needs to be updated. All my tests fail if a WARN*()
> gets hit (anywhere in the kernel, not just my own).
> After reading all the replies and thinking about this more, I find the
> pkill_on_warning actually worse than not doing anything. If you are
> concerned about exploits from warnings, the only real solution is a
> panic_on_warning. Yes, it brings down the system, but really, it has to be
> brought down anyway, because it is in need of a kernel update.

We also have LIVEPATCH to avoid bringing down the system for a kernel 
update, don't we ? So I wouldn't expect bringing down a vital system 
just for a WARN.

As far as I understand from, 
WARN() and WARN_ON() are meant to deal with those situations as 
gracefull as possible, allowing the system to continue running the best 
it can until a human controled action is taken.

So I'd expect the WARN/WARN_ON to be handled and I agree that that 
pkill_on_warning seems dangerous and unrelevant, probably more dangerous 
than doing nothing, especially as the WARN may trigger for a reason 
which has nothing to do with the running thread.


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