Re: [PATCH 0/2] add and use vma_assert_stabilised() helper

[Lorenzo Stoakes]

OK sorry to do the extremely annoying pattern of 'immediate resend' but... :)

I realised there's another silly issue here, I will have some caffeine, fix
up, and do a resend.

All - please disregard this series :>))

Cheers, Lorenzo


On Fri, Jan 16, 2026 at 10:27:46AM +0000, Lorenzo Stoakes wrote:
> Sometimes we wish to assert that a VMA is stable, that is - the VMA cannot
> be changed underneath us. This will be the case if EITHER the VMA lock or
> the mmap lock is held.
>
> We already open-code this in two places - anon_vma_name() in mm/madvise.c
> and vma_flag_set_atomic() in include/linux/mm.h.
>
> This series adds a number of pre-requisite predicates and adds
> vma_assert_stablisied() which can be used in these callsites instead.
>
> However the asserts implemented there subtly wrong - if CONFIG_PER_VMA_LOCK
> is not implemented and the mmap lock is not held, then we don't actually
> assert anything.
>
> Since this is an assert that only fires when CONFIG_DEBUG_VM is set and the
> test bots will largely be running with CONFIG_PER_VMA_LOCK set, this is
> likely in practice not a real-world issue.
>
> In any case, this series additionally fixes this issue.
>
> As part of this change we also reduce duplication of code in VMA lock
> asserts.
>
> This change also lays the foundation for future series to add this assert
> in further appropriate places to account for us now living in a world where
> a VMA may be stablised by either lock.
>
> Lorenzo Stoakes (2):
>   mm/vma: add vma_is_*_locked() helpers
>   mm: add + use vma_is_stabilised(), vma_assert_stabilised() helpers
>
>  include/linux/mm.h        |  4 +--
>  include/linux/mmap_lock.h | 55 +++++++++++++++++++++++++++++++++------
>  mm/madvise.c              |  4 +--
>  3 files changed, 49 insertions(+), 14 deletions(-)
>
> --
> 2.52.0