Re: [PATCH v7 10/17] mm: uninline the main body of vma_start_write()

[Eric Naim]

On 4/8/25 14:25, Lorenzo Stoakes wrote:
> On Mon, Apr 07, 2025 at 11:01:46PM -0700, Christoph Hellwig wrote:
>> On Tue, Apr 08, 2025 at 12:39:25PM +0800, Eric Naim wrote:
>>> The out-of-tree NVIDIA modules seem to rely on this symbol, is it possible to use EXPORT_SYMBOL() here instead of EXPORT_SYMBOL_GPL(), below is the modpost error:
>>
>> No.  They don't have any business using this.
> 
> What on _earth_ are they using this for? Is this just via the VMA flag
> manipulation functions? If it's something else, it's an unintended use of this.
> 
> Anyway, generally speaking - agreed, this is absolutely a no-go Eric. In my view
> we simply should not be using EXPORT_SYMBOL() for _any_ new symbols whatsoever.
> 
> Out-of-tree modules are simply a non-consideration for core mm code, this is a
> GPL open source project. If I had my way we'd simply revoke _all_
> EXPORT_SYMBOL()'s, not add new ones.
> 
>>
>> In fact vma_start_write should not be exported at all, just the
>> vm_flags_{set,clear,mod} helpers.
> 
> Yup, I'd rather we just kept vma_start_write() mm-internal, though of course
> kernel/fork.c (ugh) needs it (we could probably refactor that in some way to
> avoid), and literally just the PPC arch (again maybe we can find a way round
> that).
> 
> Maybe one for me to look at actually... hmm.
> 
> Anyway Eric - I wonder if this is simply the nvidia OOT driver doing a
> vm_flags_...() call and then having an issue because the lock is uninlined now?
> 
> I guess you are jut noticing this is breaking and don't know since - proprietary
> code.


This seems to be the case, upon looking a bit deeper it looks like the driver code 
is calling atleast one of vm_flags_set. I couldn't find any direct calls to {,__}vma_start_write
at first and was bit confused.

> 
> Anyway in this case, the OOT driver should just write some GPL wrapper code or
> something here. Or better yet - make the driver open source :)

Yeah, as obvious as it seems it doesn't happen on their open-sourced code :)

Either way, I'm thankful for the replies. NVIDIA *should* have probably noticed
this already and it would probably fixed in the next driver or two so I'll just
let sleeping dogs lie.


-- 
Regards,
Eric