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Message-ID: <3179f4545d3f71358da3e6c6ee18085af601b2eb.camel@perches.com>
Subject: Re: [PATCH v1 3/3] checkpatch: warn on usage of VM_BUG_ON() and
 other BUG variants
From:   Joe Perches <joe@perches.com>
To:     John Hubbard <jhubbard@nvidia.com>,
        David Hildenbrand <david@redhat.com>,
        linux-kernel@vger.kernel.org
Cc:     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>,
        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>
Date:   Thu, 22 Sep 2022 19:11:44 -0700
In-Reply-To: <d0c59eb8-baca-26fd-5f10-4a1f89bcf7b9@nvidia.com>
References: <20220920122302.99195-1-david@redhat.com>
         <20220920122302.99195-4-david@redhat.com>
         <d0c59eb8-baca-26fd-5f10-4a1f89bcf7b9@nvidia.com>
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On Thu, 2022-09-22 at 19:05 -0700, John Hubbard wrote:
> 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
[]
> > diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> > @@ -4695,12 +4695,12 @@ sub process {
> >  			}
> >  		}
> >  
> > -# avoid BUG() or BUG_ON()
> > -		if ($line =~ /\b(?:BUG|BUG_ON)\b/) {
> > +# do not use BUG() or variants
> > +		if ($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.

Not in my opinion.

> >  			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);

Fixing punctuation here would be removing the trailing period as checkpatch
only has periods for multi-sentence output messages.

And I think that "Do not crash" is a stronger statement than "Avoid crashing"
so I prefer the original suggestion but it's not a big deal either way.