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Date: Tue, 4 Oct 2022 14:32:45 +0200
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Subject: Re: [PATCH v1 1/3] coding-style.rst: document BUG() and WARN() rules
 ("do not crash the kernel")
To: Kalle Valo <kvalo@kernel.org>
References: <20220920122302.99195-1-david@redhat.com>
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From: David Hildenbrand <david@redhat.com>
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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