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

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Date:   Thu, 25 Aug 2022 14:43:02 +0300
From:   Jani Nikula <jani.nikula@...ux.intel.com>
To:     David Hildenbrand <david@...hat.com>,
        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 Thu, 25 Aug 2022, David Hildenbrand <david@...hat.com> wrote:
> 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

> CI_BUG_ON(
> -> Bad with CONFIG_DRM_I915_DEBUG
> GEM_BUG_ON(
> -> Bad with CONFIG_DRM_I915_DEBUG_GEM_ONCE

These are hidden behind debug knobs that we use in our CI to
specifically catch "should not happen" cases fast and loud. Should not
be a problem for regular users.

BR,
Jani.


> 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*\(/
>
> ?

-- 
Jani Nikula, Intel Open Source Graphics Center