Re: [PATCH v1 3/3] checkpatch: warn on usage of VM_BUG_ON() and other BUG variants

John Hubbard
2022-09-23T02:06:07Z

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@redhat.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