Re: [PATCH 2/7] mm: cma: Export cma_alloc and cma_release

["T.J. Mercier" <tjmercier@google.com>]

On Thu, Feb 26, 2026 at 2:38 AM Maxime Ripard <mripard@kernel.org> wrote:
>
> Hi David,
>
> On Thu, Feb 26, 2026 at 11:25:24AM +0100, David Hildenbrand (Arm) wrote:
> > On 2/25/26 17:41, Maxime Ripard wrote:
> > > The CMA dma-buf heap uses cma_alloc() and cma_release() to allocate and
> > > free, respectively, its CMA buffers.
> > >
> > > However, these functions are not exported. Since we want to turn the CMA
> > > heap into a module, let's export them both.
> > >
> > > Signed-off-by: Maxime Ripard <mripard@kernel.org>
> > > ---
> > >  mm/cma.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > >
> > > diff --git a/mm/cma.c b/mm/cma.c
> > > index 94b5da468a7d719e5144d33b06bcc7619c0fbcc9..be142b473f3bd41b9c7d8ba4397f018f6993d962 100644
> > > --- a/mm/cma.c
> > > +++ b/mm/cma.c
> > > @@ -949,10 +949,11 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> > >     if (page)
> > >             set_pages_refcounted(page, count);
> > >
> > >     return page;
> > >  }
> > > +EXPORT_SYMBOL_GPL(cma_alloc);
> > >
> > >  static struct cma_memrange *find_cma_memrange(struct cma *cma,
> > >             const struct page *pages, unsigned long count)
> > >  {
> > >     struct cma_memrange *cmr = NULL;
> > > @@ -1025,10 +1026,11 @@ bool cma_release(struct cma *cma, const struct page *pages,
> > >
> > >     __cma_release_frozen(cma, cmr, pages, count);
> > >
> > >     return true;
> > >  }
> > > +EXPORT_SYMBOL_GPL(cma_release);
> > >
> > >  bool cma_release_frozen(struct cma *cma, const struct page *pages,
> > >             unsigned long count)
> > >  {
> > >     struct cma_memrange *cmr;
> > >
> >
> > I'm wondering whether we want to restrict all these exports to the
> > dma-buf module only using EXPORT_SYMBOL_FOR_MODULES().
>
> TIL about EXPORT_SYMBOL_FOR_MODULES, thanks.

Ohh, ditto.

> > Especially dma_contiguous_default_area() (patch #4), I am not sure
> > whether we want arbitrary modules to mess with that.
>
> Yeah, I wasn't too fond about that one either. Alternatively, I guess we
> could turn dev_get_cma_area into a non-inlined function and export that
> instead?

I checked the history to see if dev_get_cma_area was converted to
inline at some point for performance, but it has always been that way
since 3.5. That'd be my only worry with un-inlining and exporting it.
EXPORT_SYMBOL_FOR_MODULES sounds like a better way to me.

> Or we could do both.
>
> Maxime