Re: [PATCH v2 5/6] mm: always lock new vma before inserting into vma tree

["Liam R. Howlett" <Liam.Howlett@Oracle.com>]

* Suren Baghdasaryan <surenb@google.com> [230801 18:07]:
> While it's not strictly necessary to lock a newly created vma before
> adding it into the vma tree (as long as no further changes are performed
> to it), it seems like a good policy to lock it and prevent accidental
> changes after it becomes visible to the page faults. Lock the vma before
> adding it into the vma tree.
> 
> Suggested-by: Jann Horn <jannh@google.com>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>

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

> ---
>  mm/mmap.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 3937479d0e07..850a39dee075 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -412,6 +412,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma)
>  	if (vma_iter_prealloc(&vmi))
>  		return -ENOMEM;
>  
> +	vma_start_write(vma);
> +
>  	if (vma->vm_file) {
>  		mapping = vma->vm_file->f_mapping;
>  		i_mmap_lock_write(mapping);
> @@ -477,7 +479,8 @@ static inline void vma_prepare(struct vma_prepare *vp)
>  	vma_start_write(vp->vma);
>  	if (vp->adj_next)
>  		vma_start_write(vp->adj_next);
> -	/* vp->insert is always a newly created VMA, no need for locking */
> +	if (vp->insert)
> +		vma_start_write(vp->insert);
>  	if (vp->remove)
>  		vma_start_write(vp->remove);
>  	if (vp->remove2)
> @@ -3098,6 +3101,7 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  	vma->vm_pgoff = addr >> PAGE_SHIFT;
>  	vm_flags_init(vma, flags);
>  	vma->vm_page_prot = vm_get_page_prot(flags);
> +	vma_start_write(vma);
>  	if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL))
>  		goto mas_store_fail;
>  
> @@ -3345,7 +3349,6 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
>  			get_file(new_vma->vm_file);
>  		if (new_vma->vm_ops && new_vma->vm_ops->open)
>  			new_vma->vm_ops->open(new_vma);
> -		vma_start_write(new_vma);
>  		if (vma_link(mm, new_vma))
>  			goto out_vma_link;
>  		*need_rmap_locks = false;
> -- 
> 2.41.0.585.gd2178a4bd4-goog
>