linux-kernel - Re: [PATCH v1 3/3] checkpatch: warn on usage of VM_BUG

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Date:   Thu, 22 Sep 2022 19:05:54 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-doc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org,
        Linus Torvalds <torvalds@...ux-foundation.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>,
        Dave Young <dyoung@...hat.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH v1 3/3] checkpatch: warn on usage of VM_BUG_ON() and other
 BUG variants

On 9/20/22 05:23, David Hildenbrand wrote:
> checkpatch does not point out that VM_BUG_ON() and friends should be
> avoided, however, Linus notes:
> 
>     VM_BUG_ON() has the exact same semantics as BUG_ON. It is literally
>     no different, the only difference is "we can make the code smaller
>     because these are less important". [1]
> 
> So let's warn on VM_BUG_ON() and other BUG variants as well. While at it,
> make it clearer that the kernel really shouldn't be crashed.
> 
> As there are some subsystem BUG macros that actually don't end up crashing
> the kernel -- for example, KVM_BUG_ON() -- exclude these manually.
> 
> [1] https://lore.kernel.org/r/CAHk-=wg40EAZofO16Eviaj7mfqDhZ2gVEbvfsMf6gYzspRjYvw@mail.gmail.com
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---
>  scripts/checkpatch.pl | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 79e759aac543..21f3a79aa46f 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -4695,12 +4695,12 @@ sub process {
>  			}
>  		}
>  
> -# avoid BUG() or BUG_ON()
> -		if ($line =~ /\b(?:BUG|BUG_ON)\b/) {
> +# do not use BUG() or variants
> +		if ($line =~ /\b(?!AA_|BUILD_|DCCP_|IDA_|KVM_|RWLOCK_|snd_|SPIN_)(?:[a-zA-Z_]*_)?BUG(?:_ON)?(?:_[A-Z_]+)?\s*\(/) {

Should this be a separate patch? Adding a bunch of exceptions to the BUG() rules is 
a separate and distinct thing from adding VM_BUG_ON() and other *BUG*() variants to
the mix.

>  			my $msg_level = \&WARN;
>  			$msg_level = \&CHK if ($file);
>  			&{$msg_level}("AVOID_BUG",
> -				      "Avoid crashing the kernel - try using WARN_ON & recovery code rather than BUG() or BUG_ON()\n" . $herecurr);
> +				      "Do not crash the kernel unless it is unavoidable - use WARN_ON_ONCE & recovery code (if reasonable) rather than BUG() or variants.\n" . $herecurr);

Here's a requested tweak, to clean up the output and fix punctuation:

"Avoid crashing the kernel--use WARN_ON_ONCE() plus recovery code (if feasible) instead of BUG() or variants.\n" . $herecurr);


thanks,

-- 
John Hubbard
NVIDIA