linux-kernel - Re: [PATCH RFC 1/2] coding-style.rst: document BUG() and WARN() rules ("do not crash the kernel")

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Message-ID: <29fb251b-4622-4eb6-538d-bab6ac6a76f6@nvidia.com>
Date:   Sun, 28 Aug 2022 21:49:23 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Young <dyoung@...hat.com>
Cc:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-doc@...r.kernel.org,
        kexec@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        David Laight <David.Laight@...lab.com>,
        Jonathan Corbet <corbet@....net>,
        Andy Whitcroft <apw@...onical.com>,
        Joe Perches <joe@...ches.com>,
        Dwaipayan Ray <dwaipayanray1@...il.com>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Stephen Johnston <sjohnsto@...hat.com>,
        Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCH RFC 1/2] coding-style.rst: document BUG() and WARN() rules
 ("do not crash the kernel")

On 8/28/22 20:07, Linus Torvalds wrote:
> On Sun, Aug 28, 2022 at 6:56 PM Dave Young <dyoung@...hat.com> wrote:
>>
>>> John mentioned PANIC_ON().
>>
>> I would vote for PANIC_ON(), it sounds like a good idea, because
>> BUG_ON() is not obvious and, PANIC_ON() can alert the code author that
>> this will cause a kernel panic and one will be more careful before
>> using it.
> 
> People, NO.
> 
> We're trying to get rid of BUG_ON() because it kills the machine.
> 
> Not replace it with another bogus thing that kills a machine.

OK, this guidance, and the write-up that follows it, is all very clear,
except for one point...

> 
> So no PANIC_ON(). We used to have "panic()" many many years ago, we
> got rid of it. We're not re-introducing it.

...here. I count ~1000 calls to panic() in today's kernel, to a 
function in kernel/panic.c that shows no hint of being removed, nor
even deprecated. 

$ git grep -nw panic\( | wc -l
1321

Could you please clarify that point? (I'm not trying to debate 
policy, but rather, to figure out what we should write in the
documentation of the policy.)


thanks,

-- 
John Hubbard
NVIDIA