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

[Baoquan He]

On 04/16/25 at 12:30am, Shivank Garg wrote:
> 
> 
> On 4/15/2025 6:31 PM, Baoquan He wrote:
> > On 04/15/25 at 12:52pm, Shivank Garg wrote:
> >> On 4/15/2025 8:09 AM, 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@xxxxxxxxxx>
> >>> ---
> >>>  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;
> >>>  	}
> > 
> > Thanks for reviewing.
> > 
> >>
> >> Braces around return -EINVAL seem unnecessary.
> >> They can be dropped.
> > 
> > This complys with the codeing style required in 3) Placing Braces and
> > Spaces of Documentation/process/coding-style.rst because other branches
> > are multiple statements.
> > 
> >>
> >>>  
> >>>  	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;
> >>> +	if (ret)
> >>> +		return ret;
> >>
> >> Is it safe to remove the warning, or was it critical for debugging?
> > 
> > This comes from a reported concern because va_clip() could be failed by 
> > NOTHING_FIT or kmem_cache_alloc failure. The warning here could cause
> > confusion misleading people to think vmap area management is failed.
> > 
> >>
> >>>  
> >>>  	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))
> >>> +		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. */
> >>> +		if ((unlikely(ret))) {
> >> 		    ^^		   ^^
> >> The extra parentheses are redundant and can be removed for clarity.
> > 
> > You are right, I will remove it. Thanks.
> > 
> 
> Please feel free to add following in next version.
> 
> Reviewed-by: Shivank Garg <shivankg@xxxxxxx>
> Tested-by: Shivank Garg <shivankg@xxxxxxx>

Thanks a lot for your careful reviewing and testing.

> 
> >>
> >>> +			WARN_ONCE(1, "%s error: errno (%d)\n", __func__, ret);
> >>>  			goto recovery;
> >>> +		}
> >>>  
> >>>  		/* Allocated area. */
> >>>  		va = vas[area];
> >>
> > 
>