Re: [PATCH] mm/mmap: Fix locking issues in vma_expand()

[Liam Howlett]

Andrew,

I think in my confusing post about ignoring the previous version of this
patch, you may have missed this completed solution?

Thanks,
Liam

* Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> [220712 10:49]:
> Hugh noted that the locking was mixed up in vma_expand(), revert to the
> correct order.
> 
> Fixes: b2c87578e0ea (mm/mmap: use advanced maple tree API for mmap_region())
> Suggested-by: Hugh Dickins <hughd@xxxxxxxxxx>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> ---
>  mm/mmap.c | 23 +++++++++++++----------
>  1 file changed, 13 insertions(+), 10 deletions(-)
> 
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 9eb663cde5c7..9a07bc18e6aa 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -574,7 +574,8 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
>  		if (next->anon_vma && !vma->anon_vma) {
>  			int error;
>  
> -			vma->anon_vma = next->anon_vma;
> +			anon_vma = next->anon_vma;
> +			vma->anon_vma = anon_vma;
>  			error = anon_vma_clone(vma, next);
>  			if (error)
>  				return error;
> @@ -592,16 +593,19 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
>  
>  	vma_adjust_trans_huge(vma, start, end, 0);
>  
> +	if (file) {
> +		mapping = file->f_mapping;
> +		root = &mapping->i_mmap;
> +		uprobe_munmap(vma, vma->vm_start, vma->vm_end);
> +		i_mmap_lock_write(mapping);
> +	}
> +
>  	if (anon_vma) {
>  		anon_vma_lock_write(anon_vma);
>  		anon_vma_interval_tree_pre_update_vma(vma);
>  	}
>  
>  	if (file) {
> -		mapping = file->f_mapping;
> -		root = &mapping->i_mmap;
> -		uprobe_munmap(vma, vma->vm_start, vma->vm_end);
> -		i_mmap_lock_write(mapping);
>  		flush_dcache_mmap_lock(mapping);
>  		vma_interval_tree_remove(vma, root);
>  	}
> @@ -622,16 +626,15 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
>  		__remove_shared_vm_struct(next, file, mapping);
>  	}
>  
> -	if (file) {
> -		i_mmap_unlock_write(mapping);
> -		uprobe_mmap(vma);
> -	}
> -
>  	if (anon_vma) {
>  		anon_vma_interval_tree_post_update_vma(vma);
>  		anon_vma_unlock_write(anon_vma);
>  	}
>  
> +	if (file) {
> +		i_mmap_unlock_write(mapping);
> +		uprobe_mmap(vma);
> +	}
>  
>  	if (remove_next) {
>  		if (file) {
> -- 
> 2.35.1