Re: [PATCH] slub: fix kmalloc_pagealloc_invalid_free unit test

[Nathan Chancellor]

On Mon, Aug 02, 2021 at 11:08:18AM -0700, Shakeel Butt wrote:
> The unit test kmalloc_pagealloc_invalid_free makes sure that for the
> higher order slub allocation which goes to page allocator, the free is
> called with the correct address i.e. the virtual address of the head
> page.
> 
> The commit f227f0faf63b ("slub: fix unreclaimable slab stat for bulk
> free") unified the free code paths for page allocator based slub
> allocations but instead of using the address passed by the caller, it
> extracted the address from the page. Thus making the unit test
> kmalloc_pagealloc_invalid_free moot. So, fix this by using the address
> passed by the caller.
> 
> Should we fix this? I think yes because dev expect kasan to catch these
> type of programming bugs.
> 
> Fixes: f227f0faf63b ("slub: fix unreclaimable slab stat for bulk free")
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> Reported-by: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxx>
> Cc: Roman Gushchin <guro@xxxxxx>
> Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> Cc: Christoph Lameter <cl@xxxxxxxxx>
> Cc: Pekka Enberg <penberg@xxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>

Thank you for the quick fix! It passes my tests on arm64 and x86_64 in
QEMU with a few different clang versions.

Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx>

> ---
>  mm/slub.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index af984e4990e8..60aeedc436d5 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3236,12 +3236,12 @@ struct detached_freelist {
>  	struct kmem_cache *s;
>  };
>  
> -static inline void free_nonslab_page(struct page *page)
> +static inline void free_nonslab_page(struct page *page, void *object)
>  {
>  	unsigned int order = compound_order(page);
>  
>  	VM_BUG_ON_PAGE(!PageCompound(page), page);
> -	kfree_hook(page_address(page));
> +	kfree_hook(object);
>  	mod_lruvec_page_state(page, NR_SLAB_UNRECLAIMABLE_B, -(PAGE_SIZE << order));
>  	__free_pages(page, order);
>  }
> @@ -3282,7 +3282,7 @@ int build_detached_freelist(struct kmem_cache *s, size_t size,
>  	if (!s) {
>  		/* Handle kalloc'ed objects */
>  		if (unlikely(!PageSlab(page))) {
> -			free_nonslab_page(page);
> +			free_nonslab_page(page, object);
>  			p[size] = NULL; /* mark object processed */
>  			return size;
>  		}
> @@ -4258,7 +4258,7 @@ void kfree(const void *x)
>  
>  	page = virt_to_head_page(x);
>  	if (unlikely(!PageSlab(page))) {
> -		free_nonslab_page(page);
> +		free_nonslab_page(page, object);
>  		return;
>  	}
>  	slab_free(page->slab_cache, page, object, NULL, 1, _RET_IP_);
> -- 
> 2.32.0.554.ge1b32706d8-goog
> 
>