Re: [PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG_ON() and friends

2022-08-25 Thread David Hildenbrand 
On 25.08.22 13:43, Jani Nikula wrote:
> On Thu, 25 Aug 2022, David Hildenbrand  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.
> 

I tend to agree but I don't think this is worth an exception.
VM_BUG_ON also requires CONFIG_DEBUG_VM and absolutely shouldn't
be used as I learned.

Quoting Linus:

   Really. BUG_ON() IS NOT FOR DEBUGGING. [1]

   This kind of "I don't think this can happen" is _never_ an excuse for it. [2]


For CI work, it might be sufficient to use WARN_ON_ONCE() combined with 
panic_on_warn.

[1] 
https://lore.kernel.org/all/CAHk-=wiEAH+ojSpAgx_Ep=nkpwhu8ado3v56bxccsu97oyj...@mail.gmail.com/
[2] 
https://lore.kernel.org/all/CAHk-=wg40eazofo16eviaj7mfqdhz2gvebvfsmf6gyzsprj...@mail.gmail.com/
 

-- 
Thanks,

David / dhildenb


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Re: [PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG_ON() and friends

2022-08-25 Thread Jani Nikula 
On Thu, 25 Aug 2022, David Hildenbrand  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

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Re: [PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG_ON() and friends

2022-08-25 Thread David Hildenbrand 
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


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Re: [PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG_ON() and friends

2022-08-24 Thread David Hildenbrand 
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
> 
>   if ($line =~ 
> /\b(?!KVM_|BUILD_)(?:[A-Z_]*_)?BUG(?:_ON)?(?:_[A-Z_]+)?\s*\(/

... then I'll have to scan the other cases if they do something similar
as KVM. ... well, okay, I'll do it. :)

> 
>>  my $msg_level = \
>>  $msg_level = \ if ($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);
> 
> 

Yes, thanks!

-- 
Thanks,

David / dhildenb


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Re: [PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG_ON() and friends

2022-08-24 Thread Joe Perches 
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 = \
>   $msg_level = \ if ($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);


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[PATCH RFC 2/2] checkpatch: warn on usage of VM_BUG_ON() and friends

2022-08-24 Thread David Hildenbrand 
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.

[1] 
https://lore.kernel.org/r/CAHk-=wg40eazofo16eviaj7mfqdhz2gvebvfsmf6gyzsprj...@mail.gmail.com

Signed-off-by: David Hildenbrand 
---
 scripts/checkpatch.pl | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 79e759aac543..4c18acf17032 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -4695,12 +4695,12 @@ sub process {
}
}
 
-# avoid BUG() or BUG_ON()
-   if ($line =~ /\b(?:BUG|BUG_ON)\b/) {
+# do not use BUG(), BUG_ON(), VM_BUG_ON() and friends.
+   if ($line =~ /\b(?:BUG|BUG_ON|VM_BUG_ON|VM_BUG_ON_[A-Z]+)\b/) {
my $msg_level = \
$msg_level = \ if ($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(), BUG_ON(), VM_BUG_ON(), ...\n" . $herecurr);
}
 
 # avoid LINUX_VERSION_CODE
-- 
2.37.1


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