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References: <20240531163217.1584450-1-Liam.Howlett@oracle.com> <20240531163217.1584450-2-Liam.Howlett@oracle.com>
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From: Suren Baghdasaryan <surenb@google.com>
Date: Wed, 5 Jun 2024 17:51:05 -0700
Message-ID: <CAJuCfpHqDNGM=6+TX4xE-YY91fETSM+r70ZdgxUyw=9X+3qQCQ@mail.gmail.com>
Subject: Re: [RFC PATCH 1/5] mm/mmap: Correctly position vma_iterator in __split_vma()
To: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Cc: Andrii Nakryiko <andrii.nakryiko@gmail.com>, Vlastimil Babka <vbabka@suse.cz>, 
	sidhartha.kumar@oracle.com, Matthew Wilcox <willy@infradead.org>, 
	Lorenzo Stoakes <lstoakes@gmail.com>, linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, 
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Fri, May 31, 2024 at 9:33=E2=80=AFAM Liam R. Howlett <Liam.Howlett@oracl=
e.com> wrote:
>
> The vma iterator may be left pointing to the newly created vma.  This
> happens when inserting the new vma at the end of the old vma
> (!new_below).
>
> The incorrect position in the vma iterator is not exposed currently
> since the vma iterator is repositioned in the munmap path and is not
> reused in any of the other paths.
>
> This has limited impact in the current code, but is required for future
> changes.
>
> Fixes: b2b3b886738f ("mm: don't use __vma_adjust() in __split_vma()")
> Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> ---
>  mm/mmap.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 83b4682ec85c..31d464e6a656 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2442,6 +2442,9 @@ static int __split_vma(struct vma_iterator *vmi, st=
ruct vm_area_struct *vma,
>         /* Success. */
>         if (new_below)
>                 vma_next(vmi);
> +       else
> +               vma_prev(vmi);
> +

IIUC the goal is to always point vmi to the old (original) vma? If so,
then change LGTM.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>

>         return 0;
>
>  out_free_mpol:
> --
> 2.43.0
>