Re: [PATCH 0/5] Revert cleanups for IS_ERR_OR_NULL() usage

[Danilo Krummrich]

On Thu May 28, 2026 at 10:23 PM CEST, Timur Tabi wrote:
> On Thu, 2026-05-28 at 21:44 +0200, Danilo Krummrich wrote:
>> 
>> @Timur: I do think cleaning this up is the right call in general though, and I
>> also don't think that the whole driver necessarily needs to be consistent on
>> whether IS_ERR_OR_NULL() or IS_ERR() is used -- it depends on the context
>> (although I usually prefer not to mix up NULL and ERR semantics in the first
>> place).
>> 
>> It should however be consistent in terms of what functions can actually return.
>> 
>> 	ret = foo();
>> 	if (IS_ERR_OR_NULL(ret))
>> 		return ret;
>> 
>> If foo() can never return NULL, the above is misleading, as it puts an
>> obligation on the caller to somehow handle the NULL case and come up with an
>> actual error code for it.
>
> Sure, I get that.  My point is that it's often not clear whether foo() actually can never return
> NULL.  
>
> It's been a while since I've dug through the RPC call chains in Nouveau, so my memory is a little
> hazy here.  I do remember noticing that Nouveau frequently has situations where foo() call bar1()
> and bar2(), where bar1() can return NULL but bar2() can't.  So the question is not whether foo() can
> return NULL, it's whether bar1() should not return NULL, or whether bar2() should.

If there are multiple, it has to be the superset of course.

>> So, I think it is the right call to align that to what functions can actually
>> return, but while doing this, the contract should be properly documented, such
>> that subsequent changes can be properly validated.
>
> "Properly documented" and "Nouveau" are not two things that go together.

Unfortunately -- but the changes submitted by Hongling can add the documentation
for the places that are touched.

@Hongling, can you consider this in a v2 please?

Thanks,
Danilo