Re: [PATCH] mm: prepare anon_vma before swapin rmap

[Matthew Wilcox]

On Fri, Apr 17, 2026 at 01:57:59PM +0200, David Hildenbrand (Arm) wrote:
> On 4/17/26 12:53, David Hildenbrand (Arm) wrote:
> > On 4/17/26 03:16, ZhengYuan Huang wrote:
> >> [BUG]
> >> madvise(MADV_HWPOISON) can fault a swap entry back in through
> >> get_user_pages_fast() and hit:
...
> >> I can reproduce this issue deterministically on v6.18, but I have not
> >> been able to reproduce it with the same setup on next-20260415.
> 
> Just speculating, we had
> 
> commit 3b617fd3d317bf9dd7e2c233e56eafef05734c9d
> Author: Lorenzo Stoakes <ljs@xxxxxxxxxx>
> Date:   Mon Jan 5 20:11:49 2026 +0000
> 
>     mm/vma: enforce VMA fork limit on unfaulted,faulted mremap merge too
> 
> Go into v6.19.
> 
> Maybe there was a scenario where we could have lost vma->anon_vma during
> a merge, resulting in a swapped page in an anon_vma.
> 
> If this cannot be reproduced on 6.19+,there is nothing to worry about.

... except that 6.18 is LTS so we need a fix for that kernel version.
And maybe 6.12 as well (a373baed5a9d went into 6.9, so no need to
go further back than that)