Re: [PATCH] selftests/mm: check MREMAP_DONTUNMAP mlock accounting

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

On 9/28/26 13:10, Jose A. Perez de Azpillaga wrote:
> MREMAP_DONTUNMAP keeps the source VMA in place, but clears its mlock flags
> for the whole VMA while setting them on the destination VMA.  Two cases
> leak mm->locked_vm as a result:
> 
>  - an unfaulted mlock-on-fault VMA moved behind itself self-merges, so the
>    single resulting VMA loses the flags without the accounting being
>    dropped;
> 
>  - a partial mremap() moves only part of the range, leaving the pages which
>    are not moved accounted as locked in a VMA whose flags were cleared.
> 
> Add three cases to the MREMAP_DONTUNMAP selftest which mlock() the source
> VMA, with and without MLOCK_ONFAULT, perform the operation and check that
> VmLck comes back to zero once everything is unmapped.  Each case runs in
> its own process, so it starts from a clean mm with VmLck at zero and a
> failure cannot propagate to the cases which follow.
> 
> Verified on x86_64: the three cases fail on v7.3-rc5 and pass on
> mm-unstable with the fixes from the "mm/mremap: fix two issues with
> MREMAP_DONTUNMAP" series applied.
> 
> Signed-off-by: Jose A. Perez de Azpillaga <azpijr@gmail.com>
> ---
>  tools/testing/selftests/mm/mremap_dontunmap.c | 273 +++++++++++++++++-

@Lorenzo, could something like this also be implemented (maybe with less churn)
in the vma.c selftests?

-- 
Cheers,

David