Re: [PATCH mm-hotfixes] mm/vma: remove __vma_check_mmap_hook()

[Lorenzo Stoakes]

On Mon, Apr 13, 2026 at 10:17:24PM -0700, Andrew Morton wrote:
> On Mon, 13 Apr 2026 11:57:13 +0100 Lorenzo Stoakes <ljs@xxxxxxxxxx> wrote:
>
> > Commit c50ca15dd496 ("mm: add vm_ops->mapped hook") introduced
> > __vma_check_mmap_hook() in order to assert that a driver doesn't
> > incorrectly implement both an f_op->mmap() and a vm_ops->mapped hook, the
> > latter of which would not ultimately get invoked.
> >
> > However, this did not correctly account for stacked drivers (or drivers
> > that otherwise use the compatibility layer) which might recursively call
> > an mmap_prepare hook via the compatibility layer.
> >
> > Thus the nested mmap_prepare() invocation might result in a VMA which has
> > vm_ops->mapped set with an overlaying mmap() hook, causing the
> > __vma_check_mmap_hook() to fail in vfs_mmap(), wrongly failing the
> > operation.
> >
> > This patch resolves this by simply removing the check, as we can't be
> > certain that an mmap() hook doesn't at some point invoke the compatibility
> > layer, and it's not worth trying to track it.
>
> Cool, thanks.
>
> > Fixes: c50ca15dd496 ("mm: add vm_ops->mapped hook")
>
> That's presently in flight mm.git->Linus, So I'll include this fix in
> next week's second batch of MM updates into Linus.

Ack thanks!

>
>
> > c50ca15dd496 is in mm-stable, so thought best to do as fix-patch? Will
> > leave a small bisection hazard (unfortunately) so putting this as close as
> > possible to the patch it fixes would be ideal.
>
> Yep, I did that.

Thanks!

>
>

Cheers, Lorenzo