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

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Date:   Thu, 25 Aug 2022 11:58:48 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Joe Perches <joe@...ches.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 24.08.22 18:52, Joe Perches wrote:
> 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
> 

Trying to find more possible variants and exceptions

$ git grep -h -o -E "\b[a-zA-Z]+_BUG(_ON(_[a-zA-Z]+)*)?\(" | sort | uniq
AA_BUG(
-> Ok, no BUG()
ASM_BUG(
-> Bad
BUILD_BUG(
BUILD_BUG_ON(
BUILD_BUG_ON_INVALID(
BUILD_BUG_ON_MSG(
BUILD_BUG_ON_ZERO(
-> Ok
CI_BUG_ON(
-> Bad with CONFIG_DRM_I915_DEBUG
DCCP_BUG(
DCCP_BUG_ON(
-> Ok, no BUG()
do_BUG(
-> BUG implementation, ok.
GEM_BUG_ON(
-> Bad with CONFIG_DRM_I915_DEBUG_GEM_ONCE
GLOCK_BUG_ON(
-> Bad
handle_BUG(
-> BUG implementation, ok.
IDA_BUG_ON(
KVM_BUG(
KVM_BUG_ON(
-> Ok, no BUG()
lkdtm_BUG(
paravirt_BUG(
-> bad
PROM_BUG(
-> unused, will remove
RWLOCK_BUG_ON(
-> Ok, no BUG()
snd_BUG(
snd_BUG_ON(
-> Ok, no BUG()
SNIC_BUG_ON(
-> Bad
SPIN_BUG_ON(
-> Ok, no BUG()
UNWINDER_BUG(
UNWINDER_BUG_ON(
VIRTUAL_BUG_ON(
VM_BUG_ON(
VM_BUG_ON_FOLIO(
VM_BUG_ON_MM(
VM_BUG_ON_PAGE(
VM_BUG_ON_PGFLAGS(
VM_BUG_ON_VMA(
XA_BUG_ON(
-> Bad

So an extended versions of your proposal like (ignoring do_BUG and handle_BUG, people are smart enough to figure that out)

if ($line =~ /\b(?!AA_|BUILD_|DCCP_|IDA_|KVM_|RWLOCK_|snd_|SPIN_)(?:[a-zA-Z_]*_)?BUG(?:_ON)?(?:_[A-Z_]+)?\s*\(/

?

-- 
Thanks,

David / dhildenb