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Date: Mon, 13 Apr 2026 22:17:24 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Lorenzo Stoakes <ljs@kernel.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>, Christian Brauner
 <brauner@kernel.org>, Jan Kara <jack@suse.cz>, David Hildenbrand
 <david@kernel.org>, "Liam R . Howlett" <Liam.Howlett@oracle.com>, Vlastimil
 Babka <vbabka@kernel.org>, Mike Rapoport <rppt@kernel.org>, Suren
 Baghdasaryan <surenb@google.com>, Michal Hocko <mhocko@suse.com>,
 linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
 linux-mm@kvack.org, Shinichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Subject: Re: [PATCH mm-hotfixes] mm/vma: remove __vma_check_mmap_hook()
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On Mon, 13 Apr 2026 11:57:13 +0100 Lorenzo Stoakes <ljs@kernel.org> 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.


> 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.