Re: [PATCH 4/5] mm/slub: convert object_map_lock to non-raw spinlock

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

On Fri, Aug 12, 2022 at 11:14:25AM +0200, Vlastimil Babka wrote:
> The only remaining user of object_map_lock is list_slab_objects().
> Obtaining the lock there used to happen under slab_lock() which implied
> disabling irqs on PREEMPT_RT, thus it's a raw_spinlock. With the
> slab_lock() removed, we can convert it to a normal spinlock.
> 
> Also remove the get_map()/put_map() wrappers as list_slab_objects()
> became their only remaining user.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/slub.c | 36 ++++++------------------------------
>  1 file changed, 6 insertions(+), 30 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 32b79bc3ae6d..dffb5063acbf 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -565,7 +565,7 @@ static inline bool cmpxchg_double_slab(struct kmem_cache *s, struct slab *slab,
>  
>  #ifdef CONFIG_SLUB_DEBUG
>  static unsigned long object_map[BITS_TO_LONGS(MAX_OBJS_PER_PAGE)];
> -static DEFINE_RAW_SPINLOCK(object_map_lock);
> +static DEFINE_SPINLOCK(object_map_lock);
>  
>  static void __fill_map(unsigned long *obj_map, struct kmem_cache *s,
>  		       struct slab *slab)
> @@ -599,30 +599,6 @@ static bool slab_add_kunit_errors(void)
>  static inline bool slab_add_kunit_errors(void) { return false; }
>  #endif
>  
> -/*
> - * Determine a map of objects in use in a slab.
> - *
> - * Node listlock must be held to guarantee that the slab does
> - * not vanish from under us.
> - */
> -static unsigned long *get_map(struct kmem_cache *s, struct slab *slab)
> -	__acquires(&object_map_lock)
> -{
> -	VM_BUG_ON(!irqs_disabled());
> -
> -	raw_spin_lock(&object_map_lock);
> -
> -	__fill_map(object_map, s, slab);
> -
> -	return object_map;
> -}
> -
> -static void put_map(unsigned long *map) __releases(&object_map_lock)
> -{
> -	VM_BUG_ON(map != object_map);
> -	raw_spin_unlock(&object_map_lock);
> -}
> -
>  static inline unsigned int size_from_object(struct kmem_cache *s)
>  {
>  	if (s->flags & SLAB_RED_ZONE)
> @@ -4368,21 +4344,21 @@ static void list_slab_objects(struct kmem_cache *s, struct slab *slab,
>  {
>  #ifdef CONFIG_SLUB_DEBUG
>  	void *addr = slab_address(slab);
> -	unsigned long flags;
> -	unsigned long *map;
>  	void *p;
>  
>  	slab_err(s, slab, text, s->name);
>  
> -	map = get_map(s, slab);
> +	spin_lock(&object_map_lock);
> +	__fill_map(object_map, s, slab);
> +
>  	for_each_object(p, s, addr, slab->objects) {
>  
> -		if (!test_bit(__obj_to_index(s, addr, p), map)) {
> +		if (!test_bit(__obj_to_index(s, addr, p), object_map)) {
>  			pr_err("Object 0x%p @offset=%tu\n", p, p - addr);
>  			print_tracking(s, p);
>  		}
>  	}
> -	put_map(map);
> +	spin_unlock(&object_map_lock);
>  #endif
>  }
>  
> -- 
> 2.37.1
> 

Looks good to me.
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

-- 
Thanks,
Hyeonggon