linux-kernel - Re: [PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG

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Message-ID: <3c250aa26020b2f336fd575a58d06ba26faf1f14.camel@perches.com>
Date:   Wed, 24 Aug 2022 12:52:05 -0400
From:   Joe Perches <joe@...ches.com>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     linux-mm@...ck.org, linux-doc@...r.kernel.org,
        kexec@...ts.infradead.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>,
        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>
Subject: Re: [PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG_ON() and
 friends

On Wed, 2022-08-24 at 18:31 +0200, 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 friends as well. While at it, make it
> clearer that the kernel really shouldn't be crashed.
> 
> Note that there are some other *_BUG_ON flavors, but they are not all
> bad: for example, KVM_BUG_ON() only triggers a WARN_ON_ONCE and then
> flags KVM as being buggy, so we'll not care about them for now here.
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -4695,12 +4695,12 @@ sub process {
>  			}
>  		}
>  
> -# avoid BUG() or BUG_ON()
> -		if ($line =~ /\b(?:BUG|BUG_ON)\b/) {
> +# do not use BUG(), BUG_ON(), VM_BUG_ON() and friends.
> +		if ($line =~ /\b(?:BUG|BUG_ON|VM_BUG_ON|VM_BUG_ON_[A-Z]+)\b/) {

Perhaps better as something like the below to pick up more variants

		if ($line =~ /\b(?!KVM_|BUILD_)(?:[A-Z_]*_)?BUG(?:_ON)?(?:_[A-Z_]+)?\s*\(/

>  			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);

and maybe:

				      "Do not crash the kernel unless it is unavoidable - use WARN_ON_ONCE & recovery code (if reasonable) rather than BUG() or variants\n" . $herecurr);