Re: [PATCH 5/5] mm/vmalloc.c: return explicit error value in alloc_vmap_area()

[Uladzislau Rezki <urezki@gmail.com>]

On Tue, Apr 15, 2025 at 10:39:52AM +0800, Baoquan He wrote:
> In codes of alloc_vmap_area(), it returns the upper bound 'vend' to
> indicate if the allocation is successful or failed. That is not very clear.
> 
> Here change to return explicit error values and check them to judge if
> allocation is successful.
> 
> IS_ERR_VALUE already uses unlikely() internally
> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/vmalloc.c | 34 +++++++++++++++++-----------------
>  1 file changed, 17 insertions(+), 17 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 3f38a232663b..5b21cd09b2b4 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -1715,7 +1715,7 @@ va_clip(struct rb_root *root, struct list_head *head,
>  			 */
>  			lva = kmem_cache_alloc(vmap_area_cachep, GFP_NOWAIT);
>  			if (!lva)
> -				return -1;
> +				return -ENOMEM;
>  		}
>  
>  		/*
> @@ -1729,7 +1729,7 @@ va_clip(struct rb_root *root, struct list_head *head,
>  		 */
>  		va->va_start = nva_start_addr + size;
>  	} else {
> -		return -1;
> +		return -EINVAL;
>  	}
>  
>  	if (type != FL_FIT_TYPE) {
> @@ -1758,19 +1758,19 @@ va_alloc(struct vmap_area *va,
>  
>  	/* Check the "vend" restriction. */
>  	if (nva_start_addr + size > vend)
> -		return vend;
> +		return -ERANGE;
>  
>  	/* Update the free vmap_area. */
>  	ret = va_clip(root, head, va, nva_start_addr, size);
> -	if (WARN_ON_ONCE(ret))
> -		return vend;
>
Not clear why you remove this WARN_ON by this patch. It should be
a separate patch or just keep it as is. The warning here can mean
that something is really wrong, especially if NOTHING_FIT. So we
definitely want the warning.

> +	if (ret)
> +		return ret;
>  
>  	return nva_start_addr;
>  }
>  
>  /*
>   * Returns a start address of the newly allocated area, if success.
> - * Otherwise a vend is returned that indicates failure.
> + * Otherwise an error value is returned that indicates failure.
>   */
>  static __always_inline unsigned long
>  __alloc_vmap_area(struct rb_root *root, struct list_head *head,
> @@ -1795,14 +1795,13 @@ __alloc_vmap_area(struct rb_root *root, struct list_head *head,
>  
>  	va = find_vmap_lowest_match(root, size, align, vstart, adjust_search_size);
>  	if (unlikely(!va))
> -		return vend;
> +		return -ENOENT;
>  
>  	nva_start_addr = va_alloc(va, root, head, size, align, vstart, vend);
> -	if (nva_start_addr == vend)
> -		return vend;
>  
>  #if DEBUG_AUGMENT_LOWEST_MATCH_CHECK
> -	find_vmap_lowest_match_check(root, head, size, align);
> +	if (!IS_ERR_VALUE(nva_start_addr))
>
Just keep it as it was. No need to check if addr is valid or not.

> +		find_vmap_lowest_match_check(root, head, size, align);
>  #endif
>  
>  	return nva_start_addr;
> @@ -1932,7 +1931,7 @@ node_alloc(unsigned long size, unsigned long align,
>  	struct vmap_area *va;
>  
>  	*vn_id = 0;
> -	*addr = vend;
> +	*addr = -EINVAL;
>  
>  	/*
>  	 * Fallback to a global heap if not vmalloc or there
> @@ -2012,20 +2011,20 @@ static struct vmap_area *alloc_vmap_area(unsigned long size,
>  	}
>  
>  retry:
> -	if (addr == vend) {
> +	if (IS_ERR_VALUE(addr)) {
>  		preload_this_cpu_lock(&free_vmap_area_lock, gfp_mask, node);
>  		addr = __alloc_vmap_area(&free_vmap_area_root, &free_vmap_area_list,
>  			size, align, vstart, vend);
>  		spin_unlock(&free_vmap_area_lock);
>  	}
>  
> -	trace_alloc_vmap_area(addr, size, align, vstart, vend, addr == vend);
> +	trace_alloc_vmap_area(addr, size, align, vstart, vend, IS_ERR_VALUE(addr));
>  
>  	/*
> -	 * If an allocation fails, the "vend" address is
> +	 * If an allocation fails, the error value is
>  	 * returned. Therefore trigger the overflow path.
>  	 */
> -	if (unlikely(addr == vend))
> +	if (IS_ERR_VALUE(addr))
>  		goto overflow;
>  
>  	va->va_start = addr;
> @@ -4753,9 +4752,10 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>  
>  		ret = va_clip(&free_vmap_area_root,
>  			&free_vmap_area_list, va, start, size);
> -		if (WARN_ON_ONCE(unlikely(ret)))
> -			/* It is a BUG(), but trigger recovery instead. */
Keep the comment.

> +		if ((unlikely(ret))) {
> +			WARN_ONCE(1, "%s error: errno (%d)\n", __func__, ret);
>  			goto recovery;
> +		}
>

--
Uladzislau Rezki