Re: [PATCH mm-hotfixes] mm: remove unnecessary and incorrect mmap lock assert

["David Hildenbrand (Red Hat)" <david@kernel.org>]

On 1/14/26 12:56, Lorenzo Stoakes wrote:
> This check was introduced by commit 42fc541404f2 ("mmap locking API: add
> mmap_assert_locked() and mmap_assert_write_locked()") which replaced a
> VM_BUG_ON_VMA() over rwsem_is_locked from commit a00cc7d9dd93 ("mm, x86:
> add support for PUD-sized transparent hugepages"), i.e. the commit that
> introduced PUD THPs.
> 
> These seem to be careful asserts introduced to ensure that locks are held
> in general, however for a zap we require that VMAs are kept stable, and
> this is a requirement that has held perfectly well for a long time.
> 
> These were long before VMA locks and thus there appears to be no reason to
> think this is assert is there for anything other than 'stabilised VMA'.
> 
> Asserting that the VMA under examination is stable only in the case of a
> THP PUD is strange and unnecessary. If we wish to be careful and assert
> such things, we should do so at the zap level.
> 
> However in any case the current situation is already simply incorrect - a
> VMA lock suffices here.
> 
> Remove the assert for now as it is unnecessarily, incorrect and unhelpful,
> subsequent work can introduce an assert in general for zapping if required.
> 
> Fixes: 2ab7f1bbafc9 ("mm/madvise: allow guard page install/remove under VMA lock")
> Reported-by: Chris Mason <clm@meta.com>
> Closes: https://lore.kernel.org/all/20260113220856.2358195-1-clm@meta.com/
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

Makes sense to me

Acked-by: David Hildenbrand (Red Hat) <david@kernel.org>

-- 
Cheers

David