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

[Lorenzo Stoakes]

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.

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 :)