Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <31f20ddf-cd41-69b5-2875-2d738b166ae2@redhat.com>
Date:   Tue, 4 Oct 2022 14:32:45 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.3.0
Subject: Re: [PATCH v1 1/3] coding-style.rst: document BUG() and WARN() rules
 ("do not crash the kernel")
Content-Language: en-US
To:     Kalle Valo <kvalo@kernel.org>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        linux-doc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Ingo Molnar <mingo@kernel.org>,
        David Laight <David.Laight@ACULAB.COM>,
        Jonathan Corbet <corbet@lwn.net>,
        Andy Whitcroft <apw@canonical.com>,
        Joe Perches <joe@perches.com>,
        Dwaipayan Ray <dwaipayanray1@gmail.com>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>,
        Baoquan He <bhe@redhat.com>, Vivek Goyal <vgoyal@redhat.com>,
        Dave Young <dyoung@redhat.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Nicholas Piggin <npiggin@gmail.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>
References: <20220920122302.99195-1-david@redhat.com>
 <20220920122302.99195-2-david@redhat.com> <87pmfp8hnj.fsf@kernel.org>
 <d1ceedca-b28e-c47e-aa0d-aa1cb36d12b9@redhat.com> <87leq64m20.fsf@kernel.org>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
In-Reply-To: <87leq64m20.fsf@kernel.org>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 26.09.22 09:44, Kalle Valo wrote:
> David Hildenbrand <david@redhat.com> writes:
> 
>>>> +Use WARN_ON_ONCE() rather than WARN() or WARN_ON()
>>>> +**************************************************
>>>> +
>>>> +WARN_ON_ONCE() is generally preferred over WARN() or WARN_ON(), because it
>>>> +is common for a given warning condition, if it occurs at all, to occur
>>>> +multiple times. This can fill up and wrap the kernel log, and can even slow
>>>> +the system enough that the excessive logging turns into its own, additional
>>>> +problem.
>>>
>>> FWIW I have had cases where WARN() messages caused a reboot, maybe
>>> mention that here? In my case the logging was so excessive that the
>>> watchdog wasn't updated and in the end the device was forcefully
>>> rebooted.
>>>
>>
>> That should be covered by the last part, no? What would be your suggestion?
> 
> I was just thinking that maybe make it more obvious that even WARN_ON()
> can crash the system, something along these lines:
> 
> "..., additional problem like stalling the system so much that it causes
> a reboot."

Hi Kalle,

sorry for the late reply. Jonathan already queued v2 and sent it upstream.

I think that's it is already covered by the statement and that the 
additional example isn't required -- most of us learned the hard way 
that "excessive logging turns into its own problem" includes all weird 
kinds of kernel crashes. A panic/reboot due to a watchdog not firing is 
one such possible outcome.

Thanks!

-- 
Thanks,

David / dhildenb