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Subject: Re: [PATCH] Introduce the pkill_on_warn boot parameter
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Petr Mladek <pmladek@suse.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Alexander Popov <alex.popov@linux.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Joerg Roedel <jroedel@suse.de>,
        Maciej Rozycki <macro@orcam.me.uk>,
        Muchun Song <songmuchun@bytedance.com>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Robin Murphy <robin.murphy@arm.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Kees Cook <keescook@chromium.org>,
        Luis Chamberlain <mcgrof@kernel.org>, Wei Liu <wl@xen.org>,
        John Ogness <john.ogness@linutronix.de>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Jann Horn <jannh@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
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        David S Miller <davem@davemloft.net>,
        Borislav Petkov <bp@alien8.de>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-hardening@vger.kernel.org,
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        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
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From:   Alexey Khoroshilov <khoroshilov@ispras.ru>
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Message-ID: <64be87a7-bb1f-5578-a526-b7d064fcfea3@ispras.ru>
Date:   Wed, 27 Jul 2022 20:47:41 +0300
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On 27.07.2022 19:42, Linus Torvalds wrote:
> On Wed, Jul 27, 2022 at 9:17 AM Alexey Khoroshilov
> <khoroshilov@ispras.ru> wrote:
>>
>> We see a number of cases where WARNING is used to inform userspace that
>> it is doing something wrong, e.g.
>> https://elixir.bootlin.com/linux/v5.19-rc8/source/net/can/j1939/socket.c#L181
>> https://elixir.bootlin.com/linux/v5.19-rc8/source/drivers/video/fbdev/core/fbmem.c#L1023
> 
> That first case is entirely bogus.
> 
> WARN_ON() should only be used for "This cannot happen, but if it does,
> I want to know how we got here".
> 
> But the second case is fine: Using "pr_warn()" is fine. A kernel
> warning (without a backtrace) is a normal thing for something that is
> deprecated or questionable, and you want to tell the user that "this
> app is doing something wrong".

Agree with the only note that I like the requirement:

* Do not include "BUG"/"WARNING" in format strings manually to make
* these conditions distinguishable from kernel issues.

very much.

Thank you,
Alexey