linux-kernel - Re: [PATCH v7 10/17] mm: uninline the main body of vma_start

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Message-ID: <CAJuCfpF=pUQFpbGn4kGjpW4dObcMbo8CTFLGK09npGi4W4MCsg@mail.gmail.com>
Date: Tue, 8 Apr 2025 10:09:57 -0700
From: Suren Baghdasaryan <surenb@...gle.com>
To: Eric Naim <dnaim@...hyos.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Christoph Hellwig <hch@...radead.org>, 
	Vlastimil Babka <vbabka@...e.cz>, akpm@...ux-foundation.org, peterz@...radead.org, 
	willy@...radead.org, liam.howlett@...cle.com, mhocko@...e.com, 
	hannes@...xchg.org, mjguzik@...il.com, oliver.sang@...el.com, 
	mgorman@...hsingularity.net, david@...hat.com, peterx@...hat.com, 
	oleg@...hat.com, dave@...olabs.net, paulmck@...nel.org, brauner@...nel.org, 
	dhowells@...hat.com, hdanton@...a.com, hughd@...gle.com, 
	lokeshgidra@...gle.com, minchan@...gle.com, jannh@...gle.com, 
	shakeel.butt@...ux.dev, souravpanda@...gle.com, pasha.tatashin@...een.com, 
	klarasmodin@...il.com, corbet@....net, linux-doc@...r.kernel.org, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v7 10/17] mm: uninline the main body of vma_start_write()

On Tue, Apr 8, 2025 at 12:52 AM Eric Naim <dnaim@...hyos.org> wrote:
>
> 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.

I agree that EXPORT_SYMBOL_GPL() should be enough as far as exporting goes.

>
> >
> > 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