Re: [PATCH v3 04/16] mm/mmap: Extract the gathering of vmas from do_vmi_align_munmap()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Thu, Jul 04, 2024 at 02:27:06PM GMT, Liam R. Howlett wrote:
> Create vmi_gather_munmap_vmas() to handle the gathering of vmas into a
> detached maple tree for removal later.  Part of the gathering is the
> splitting of vmas that span the boundary.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> ---
>  mm/mmap.c | 82 +++++++++++++++++++++++++++++++++++++++----------------
>  1 file changed, 58 insertions(+), 24 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 411798f46932..8dc8ffbf9d8d 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -2656,32 +2656,29 @@ vmi_complete_munmap_vmas(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  }
>
>  /*
> - * do_vmi_align_munmap() - munmap the aligned region from @start to @end.
> + * vmi_gather_munmap_vmas() - Put all VMAs within a range into a maple tree
> + * for removal at a later date.  Handles splitting first and last if necessary
> + * and marking the vmas as isolated.
> + *
>   * @vmi: The vma iterator
>   * @vma: The starting vm_area_struct
>   * @mm: The mm_struct
>   * @start: The aligned start address to munmap.
>   * @end: The aligned end address to munmap.
>   * @uf: The userfaultfd list_head
> - * @unlock: Set to true to drop the mmap_lock.  unlocking only happens on
> - * success.
> + * @mas_detach: The maple state tracking the detached tree

Missing the locked_vm parameter.

>   *
> - * Return: 0 on success and drops the lock if so directed, error and leaves the
> - * lock held otherwise.
> + * Return: 0 on success
>   */
>  static int
> -do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
> +vmi_gather_munmap_vmas(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  		    struct mm_struct *mm, unsigned long start,
> -		    unsigned long end, struct list_head *uf, bool unlock)
> +		    unsigned long end, struct list_head *uf,
> +		    struct ma_state *mas_detach, unsigned long *locked_vm)
>  {
>  	struct vm_area_struct *next = NULL;
> -	struct maple_tree mt_detach;
>  	int count = 0;
>  	int error = -ENOMEM;
> -	unsigned long locked_vm = 0;
> -	MA_STATE(mas_detach, &mt_detach, 0, 0);
> -	mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
> -	mt_on_stack(mt_detach);
>
>  	/*
>  	 * If we need to split any vma, do it now to save pain later.
> @@ -2720,15 +2717,14 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  				goto end_split_failed;
>  		}
>  		vma_start_write(next);
> -		mas_set(&mas_detach, count);
> -		error = mas_store_gfp(&mas_detach, next, GFP_KERNEL);
> +		mas_set(mas_detach, count++);
> +		if (next->vm_flags & VM_LOCKED)
> +			*locked_vm += vma_pages(next);
> +
> +		error = mas_store_gfp(mas_detach, next, GFP_KERNEL);
>  		if (error)
>  			goto munmap_gather_failed;
>  		vma_mark_detached(next, true);
> -		if (next->vm_flags & VM_LOCKED)
> -			locked_vm += vma_pages(next);
> -
> -		count++;
>  		if (unlikely(uf)) {
>  			/*
>  			 * If userfaultfd_unmap_prep returns an error the vmas
> @@ -2753,7 +2749,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  #if defined(CONFIG_DEBUG_VM_MAPLE_TREE)
>  	/* Make sure no VMAs are about to be lost. */
>  	{
> -		MA_STATE(test, &mt_detach, 0, 0);
> +		MA_STATE(test, mas_detach->tree, 0, 0);
>  		struct vm_area_struct *vma_mas, *vma_test;
>  		int test_count = 0;
>
> @@ -2773,6 +2769,48 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  	while (vma_iter_addr(vmi) > start)
>  		vma_iter_prev_range(vmi);
>
> +	return 0;
> +
> +userfaultfd_error:
> +munmap_gather_failed:
> +end_split_failed:
> +	abort_munmap_vmas(mas_detach);
> +start_split_failed:
> +map_count_exceeded:
> +	return error;
> +}
> +
> +/*
> + * do_vmi_align_munmap() - munmap the aligned region from @start to @end.
> + * @vmi: The vma iterator
> + * @vma: The starting vm_area_struct
> + * @mm: The mm_struct
> + * @start: The aligned start address to munmap.
> + * @end: The aligned end address to munmap.
> + * @uf: The userfaultfd list_head
> + * @unlock: Set to true to drop the mmap_lock.  unlocking only happens on
> + * success.
> + *
> + * Return: 0 on success and drops the lock if so directed, error and leaves the
> + * lock held otherwise.
> + */
> +static int
> +do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
> +		    struct mm_struct *mm, unsigned long start,
> +		    unsigned long end, struct list_head *uf, bool unlock)
> +{
> +	struct maple_tree mt_detach;
> +	MA_STATE(mas_detach, &mt_detach, 0, 0);
> +	mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
> +	mt_on_stack(mt_detach);
> +	int error;
> +	unsigned long locked_vm = 0;
> +
> +	error = vmi_gather_munmap_vmas(vmi, vma, mm, start, end, uf,
> +				       &mas_detach, &locked_vm);
> +	if (error)
> +		goto gather_failed;
> +
>  	error = vma_iter_clear_gfp(vmi, start, end, GFP_KERNEL);
>  	if (error)
>  		goto clear_tree_failed;
> @@ -2783,12 +2821,8 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  	return 0;
>
>  clear_tree_failed:
> -userfaultfd_error:
> -munmap_gather_failed:
> -end_split_failed:
>  	abort_munmap_vmas(&mas_detach);
> -start_split_failed:
> -map_count_exceeded:
> +gather_failed:
>  	validate_mm(mm);
>  	return error;
>  }
> --
> 2.43.0
>
>

Other than trivial comment error, LGTM:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>