Re: [PATCH v2] mm/vma: Return the exact errno in vms_gather_munmap_vmas()

[Liam R. Howlett]

* Xiao Yang <ice_yangxiao@xxxxxxx> [240909 08:56]:
> __split_vma() and mas_store_gfp() returns several types of errno on
> failure so don't ignore them in vms_gather_munmap_vmas(). For example,
> __split_vma() returns -EINVAL when an unaligned huge page is unmapped.
> This issue is reproduced by ltp memfd_create03 test.
> 
> Don't initialise the error variable and assign it when a failure
> actually occurs.
> 
> Fixes: 6898c9039bc8 ("mm/vma: extract the gathering of vmas from do_vmi_align_munmap()")
> Signed-off-by: Xiao Yang <ice_yangxiao@xxxxxxx>
> Suggested-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-lkp/202409081536.d283a0fb-oliver.sang@xxxxxxxxx
> ---
>  mm/vma.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/vma.c b/mm/vma.c
> index 8d1686fc8d5a..dc5355d99a18 100644
> --- a/mm/vma.c
> +++ b/mm/vma.c
> @@ -1171,13 +1171,13 @@ void vms_complete_munmap_vmas(struct vma_munmap_struct *vms,
>   * @vms: The vma munmap struct
>   * @mas_detach: The maple state tracking the detached tree
>   *
> - * Return: 0 on success, -EPERM on mseal vmas, -ENOMEM otherwise
> + * Return: 0 on success, error otherwise
>   */
>  int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
>  		struct ma_state *mas_detach)
>  {
>  	struct vm_area_struct *next = NULL;
> -	int error = -ENOMEM;
> +	int error;
>  
>  	/*
>  	 * If we need to split any vma, do it now to save pain later.
> @@ -1191,8 +1191,10 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
>  		 * its limit temporarily, to help free resources as expected.
>  		 */
>  		if (vms->end < vms->vma->vm_end &&
> -		    vms->vma->vm_mm->map_count >= sysctl_max_map_count)
> +		    vms->vma->vm_mm->map_count >= sysctl_max_map_count) {
> +			error = -ENOMEM;
>  			goto map_count_exceeded;
> +		}
>  
>  		/* Don't bother splitting the VMA if we can't unmap it anyway */
>  		if (!can_modify_vma(vms->vma)) {
> @@ -1200,7 +1202,8 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
>  			goto start_split_failed;
>  		}
>  
> -		if (__split_vma(vms->vmi, vms->vma, vms->start, 1))
> +		error = __split_vma(vms->vmi, vms->vma, vms->start, 1);
> +		if (error)
>  			goto start_split_failed;
>  	}
>  	vms->prev = vma_prev(vms->vmi);
> @@ -1220,12 +1223,14 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
>  		}
>  		/* Does it split the end? */
>  		if (next->vm_end > vms->end) {
> -			if (__split_vma(vms->vmi, next, vms->end, 0))
> +			error = __split_vma(vms->vmi, next, vms->end, 0);
> +			if (error)
>  				goto end_split_failed;
>  		}
>  		vma_start_write(next);
>  		mas_set(mas_detach, vms->vma_count++);
> -		if (mas_store_gfp(mas_detach, next, GFP_KERNEL))
> +		error = mas_store_gfp(mas_detach, next, GFP_KERNEL);
> +		if (error)
>  			goto munmap_gather_failed;
>  
>  		vma_mark_detached(next, true);
> @@ -1255,8 +1260,8 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
>  			 * split, despite we could. This is unlikely enough
>  			 * failure that it's not worth optimizing it for.
>  			 */
> -			if (userfaultfd_unmap_prep(next, vms->start, vms->end,
> -						   vms->uf))
> +			error = userfaultfd_unmap_prep(next, vms->start, vms->end, vms->uf);

This line is too long.

> +			if (error)
>  				goto userfaultfd_error;

Good you saw this issue, I was going to point it out.

>  		}
>  #ifdef CONFIG_DEBUG_VM_MAPLE_TREE
> -- 
> 2.46.0
> 
> 

Besides the line over 80 characters, this looks good to me and should be
squashed into my series.

Thanks,
Liam