linux-kernel - Re: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or expanding it

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Message-ID: <20230223202011.dahh6cidqxhzoxne@revolver>
Date:   Thu, 23 Feb 2023 15:20:11 -0500
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, michel@...pinasse.org,
        jglisse@...gle.com, mhocko@...e.com, vbabka@...e.cz,
        hannes@...xchg.org, mgorman@...hsingularity.net, dave@...olabs.net,
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Subject: Re: [PATCH v3 17/35] mm/mmap: write-lock VMA before shrinking or
 expanding it

Reviewed-by: Liam R. Howlett <Liam.Howlett@...cle.com>

* Suren Baghdasaryan <surenb@...gle.com> [230216 00:18]:
> vma_expand and vma_shrink change VMA boundaries. Expansion might also
> result in freeing of an adjacent VMA. Write-lock affected VMAs to prevent
> concurrent page faults.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>  mm/mmap.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index ec2f8d0af280..f079e5bbcd57 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -674,6 +674,9 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  		ret = dup_anon_vma(vma, next);
>  		if (ret)
>  			return ret;
> +
> +		/* Lock the VMA  before removing it */
> +		vma_start_write(next);
>  	}
>  
>  	init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL);
> @@ -686,6 +689,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  	if (vma_iter_prealloc(vmi))
>  		goto nomem;
>  
> +	vma_start_write(vma);
>  	vma_adjust_trans_huge(vma, start, end, 0);
>  	/* VMA iterator points to previous, so set to start if necessary */
>  	if (vma_iter_addr(vmi) != start)
> @@ -725,6 +729,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  	if (vma_iter_prealloc(vmi))
>  		return -ENOMEM;
>  
> +	vma_start_write(vma);
>  	init_vma_prep(&vp, vma);
>  	vma_adjust_trans_huge(vma, start, end, 0);
>  	vma_prepare(&vp);
> -- 
> 2.39.1
>