Re: [PATCH 08/12] mm, slub: refactor free debug processing

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

On Mon, Nov 21, 2022 at 06:11:58PM +0100, Vlastimil Babka wrote:
> Since commit c7323a5ad078 ("mm/slub: restrict sysfs validation to debug
> caches and make it safe"), caches with debugging enabled use the
> free_debug_processing() function to do both freeing checks and actual
> freeing to partial list under list_lock, bypassing the fast paths.
> 
> We will want to use the same path for CONFIG_SLUB_TINY, but without the
> debugging checks, so refactor the code so that free_debug_processing()
> does only the checks, while the freeing is handled by a new function
> free_to_partial_list().
> 
> For consistency, change return parameter alloc_debug_processing() from
> int to bool and correct the !SLUB_DEBUG variant to return true and not
> false. This didn't matter until now, but will in the following changes.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/slub.c | 154 +++++++++++++++++++++++++++++-------------------------
>  1 file changed, 83 insertions(+), 71 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index bf726dd00f7d..fd56d7cca9c2 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1368,7 +1368,7 @@ static inline int alloc_consistency_checks(struct kmem_cache *s,
>  	return 1;
>  }
>  
> -static noinline int alloc_debug_processing(struct kmem_cache *s,
> +static noinline bool alloc_debug_processing(struct kmem_cache *s,
>  			struct slab *slab, void *object, int orig_size)
>  {
>  	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
> @@ -1380,7 +1380,7 @@ static noinline int alloc_debug_processing(struct kmem_cache *s,
>  	trace(s, slab, object, 1);
>  	set_orig_size(s, object, orig_size);
>  	init_object(s, object, SLUB_RED_ACTIVE);
> -	return 1;
> +	return true;
>  
>  bad:
>  	if (folio_test_slab(slab_folio(slab))) {
> @@ -1393,7 +1393,7 @@ static noinline int alloc_debug_processing(struct kmem_cache *s,
>  		slab->inuse = slab->objects;
>  		slab->freelist = NULL;
>  	}
> -	return 0;
> +	return false;
>  }
>  
>  static inline int free_consistency_checks(struct kmem_cache *s,
> @@ -1646,17 +1646,17 @@ static inline void setup_object_debug(struct kmem_cache *s, void *object) {}
>  static inline
>  void setup_slab_debug(struct kmem_cache *s, struct slab *slab, void *addr) {}
>  
> -static inline int alloc_debug_processing(struct kmem_cache *s,
> -	struct slab *slab, void *object, int orig_size) { return 0; }
> +static inline bool alloc_debug_processing(struct kmem_cache *s,
> +	struct slab *slab, void *object, int orig_size) { return true; }
>  
> -static inline void free_debug_processing(
> -	struct kmem_cache *s, struct slab *slab,
> -	void *head, void *tail, int bulk_cnt,
> -	unsigned long addr) {}
> +static inline bool free_debug_processing(struct kmem_cache *s,
> +	struct slab *slab, void *head, void *tail, int *bulk_cnt,
> +	unsigned long addr, depot_stack_handle_t handle) { return true; }
>  
>  static inline void slab_pad_check(struct kmem_cache *s, struct slab *slab) {}
>  static inline int check_object(struct kmem_cache *s, struct slab *slab,
>  			void *object, u8 val) { return 1; }
> +static inline depot_stack_handle_t set_track_prepare(void) { return 0; }
>  static inline void set_track(struct kmem_cache *s, void *object,
>  			     enum track_item alloc, unsigned long addr) {}
>  static inline void add_full(struct kmem_cache *s, struct kmem_cache_node *n,
> @@ -2833,38 +2833,28 @@ static inline unsigned long node_nr_objs(struct kmem_cache_node *n)
>  }
>  
>  /* Supports checking bulk free of a constructed freelist */
> -static noinline void free_debug_processing(
> -	struct kmem_cache *s, struct slab *slab,
> -	void *head, void *tail, int bulk_cnt,
> -	unsigned long addr)
> +static inline bool free_debug_processing(struct kmem_cache *s,
> +	struct slab *slab, void *head, void *tail, int *bulk_cnt,
> +	unsigned long addr, depot_stack_handle_t handle)
>  {
> -	struct kmem_cache_node *n = get_node(s, slab_nid(slab));
> -	struct slab *slab_free = NULL;
> +	bool checks_ok = false;
>  	void *object = head;
>  	int cnt = 0;
> -	unsigned long flags;
> -	bool checks_ok = false;
> -	depot_stack_handle_t handle = 0;
> -
> -	if (s->flags & SLAB_STORE_USER)
> -		handle = set_track_prepare();
> -
> -	spin_lock_irqsave(&n->list_lock, flags);
>  
>  	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
>  		if (!check_slab(s, slab))
>  			goto out;
>  	}
>  
> -	if (slab->inuse < bulk_cnt) {
> +	if (slab->inuse < *bulk_cnt) {
>  		slab_err(s, slab, "Slab has %d allocated objects but %d are to be freed\n",
> -			 slab->inuse, bulk_cnt);
> +			 slab->inuse, *bulk_cnt);
>  		goto out;
>  	}
>  
>  next_object:
>  
> -	if (++cnt > bulk_cnt)
> +	if (++cnt > *bulk_cnt)
>  		goto out_cnt;
>  
>  	if (s->flags & SLAB_CONSISTENCY_CHECKS) {
> @@ -2886,57 +2876,18 @@ static noinline void free_debug_processing(
>  	checks_ok = true;
>  
>  out_cnt:
> -	if (cnt != bulk_cnt)
> +	if (cnt != *bulk_cnt) {
>  		slab_err(s, slab, "Bulk free expected %d objects but found %d\n",
> -			 bulk_cnt, cnt);
> -
> -out:
> -	if (checks_ok) {
> -		void *prior = slab->freelist;
> -
> -		/* Perform the actual freeing while we still hold the locks */
> -		slab->inuse -= cnt;
> -		set_freepointer(s, tail, prior);
> -		slab->freelist = head;
> -
> -		/*
> -		 * If the slab is empty, and node's partial list is full,
> -		 * it should be discarded anyway no matter it's on full or
> -		 * partial list.
> -		 */
> -		if (slab->inuse == 0 && n->nr_partial >= s->min_partial)
> -			slab_free = slab;
> -
> -		if (!prior) {
> -			/* was on full list */
> -			remove_full(s, n, slab);
> -			if (!slab_free) {
> -				add_partial(n, slab, DEACTIVATE_TO_TAIL);
> -				stat(s, FREE_ADD_PARTIAL);
> -			}
> -		} else if (slab_free) {
> -			remove_partial(n, slab);
> -			stat(s, FREE_REMOVE_PARTIAL);
> -		}
> +			 *bulk_cnt, cnt);
> +		*bulk_cnt = cnt;
>  	}
>  
> -	if (slab_free) {
> -		/*
> -		 * Update the counters while still holding n->list_lock to
> -		 * prevent spurious validation warnings
> -		 */
> -		dec_slabs_node(s, slab_nid(slab_free), slab_free->objects);
> -	}
> -
> -	spin_unlock_irqrestore(&n->list_lock, flags);
> +out:
>  
>  	if (!checks_ok)
>  		slab_fix(s, "Object at 0x%p not freed", object);
>  
> -	if (slab_free) {
> -		stat(s, FREE_SLAB);
> -		free_slab(s, slab_free);
> -	}
> +	return checks_ok;
>  }
>  #endif /* CONFIG_SLUB_DEBUG */
>  
> @@ -3453,6 +3404,67 @@ void *kmem_cache_alloc_node(struct kmem_cache *s, gfp_t gfpflags, int node)
>  }
>  EXPORT_SYMBOL(kmem_cache_alloc_node);
>  
> +static noinline void free_to_partial_list(
> +	struct kmem_cache *s, struct slab *slab,
> +	void *head, void *tail, int bulk_cnt,
> +	unsigned long addr)
> +{
> +	struct kmem_cache_node *n = get_node(s, slab_nid(slab));
> +	struct slab *slab_free = NULL;
> +	int cnt = bulk_cnt;
> +	unsigned long flags;
> +	depot_stack_handle_t handle = 0;
> +
> +	if (s->flags & SLAB_STORE_USER)
> +		handle = set_track_prepare();
> +
> +	spin_lock_irqsave(&n->list_lock, flags);
> +
> +	if (free_debug_processing(s, slab, head, tail, &cnt, addr, handle)) {
> +		void *prior = slab->freelist;
> +
> +		/* Perform the actual freeing while we still hold the locks */
> +		slab->inuse -= cnt;
> +		set_freepointer(s, tail, prior);
> +		slab->freelist = head;
> +
> +		/*
> +		 * If the slab is empty, and node's partial list is full,
> +		 * it should be discarded anyway no matter it's on full or
> +		 * partial list.
> +		 */
> +		if (slab->inuse == 0 && n->nr_partial >= s->min_partial)
> +			slab_free = slab;
> +
> +		if (!prior) {
> +			/* was on full list */
> +			remove_full(s, n, slab);
> +			if (!slab_free) {
> +				add_partial(n, slab, DEACTIVATE_TO_TAIL);
> +				stat(s, FREE_ADD_PARTIAL);
> +			}
> +		} else if (slab_free) {
> +			remove_partial(n, slab);
> +			stat(s, FREE_REMOVE_PARTIAL);
> +		}
> +	}
> +
> +	if (slab_free) {
> +		/*
> +		 * Update the counters while still holding n->list_lock to
> +		 * prevent spurious validation warnings
> +		 */
> +		dec_slabs_node(s, slab_nid(slab_free), slab_free->objects);
> +	}
> +
> +	spin_unlock_irqrestore(&n->list_lock, flags);
> +
> +	if (slab_free) {
> +		stat(s, FREE_SLAB);
> +		free_slab(s, slab_free);
> +	}
> +}
> +
>  /*
>   * Slow path handling. This may still be called frequently since objects
>   * have a longer lifetime than the cpu slabs in most processing loads.
> @@ -3479,7 +3491,7 @@ static void __slab_free(struct kmem_cache *s, struct slab *slab,
>  		return;
>  
>  	if (kmem_cache_debug(s)) {
> -		free_debug_processing(s, slab, head, tail, cnt, addr);
> +		free_to_partial_list(s, slab, head, tail, cnt, addr);
>  		return;
>  	}
>  
> -- 
> 2.38.1
>

Looks good to me.

Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

-- 
Thanks,
Hyeonggon