Commit 41bec7c3 authored by Vlastimil Babka's avatar Vlastimil Babka
Browse files

mm/slub: remove slab_lock() usage for debug operations 



All alloc and free operations on debug caches are now serialized by
n->list_lock, so we can remove slab_lock() usage in validate_slab()
and list_slab_objects() as those also happen under n->list_lock.

Note the usage in list_slab_objects() could happen even on non-debug
caches, but only during cache shutdown time, so there should not be any
parallel freeing activity anymore. Except for buggy slab users, but in
that case the slab_lock() would not help against the common cmpxchg
based fast paths (in non-debug caches) anyway.

Also adjust documentation comments accordingly.

Suggested-by: default avatarHyeonggon Yoo <42.hyeyoo@gmail.com>
Signed-off-by: default avatarVlastimil Babka <vbabka@suse.cz>
Reviewed-by: default avatarHyeonggon Yoo <42.hyeyoo@gmail.com>
Acked-by: default avatarDavid Rientjes <rientjes@google.com>
parent c7323a5a

mm/slub.c

+8 −11
Original line number Diff line number Diff line
@@ -50,7 +50,7 @@ 
 *   1. slab_mutex (Global Mutex)

 *   2. node->list_lock (Spinlock)

 *   3. kmem_cache->cpu_slab->lock (Local lock)

 *   4. slab_lock(slab) (Only on some arches or for debugging)

 *   4. slab_lock(slab) (Only on some arches)

 *   5. object_map_lock (Only for debugging)

 *

 *   slab_mutex
@@ -64,8 +64,9 @@ 
 *   The slab_lock is a wrapper around the page lock, thus it is a bit

 *   spinlock.

 *

 *   The slab_lock is only used for debugging and on arches that do not

 *   have the ability to do a cmpxchg_double. It only protects:

 *   The slab_lock is only used on arches that do not have the ability

 *   to do a cmpxchg_double. It only protects:

 *

 *	A. slab->freelist	-> List of free objects in a slab

 *	B. slab->inuse		-> Number of objects in use

 *	C. slab->objects	-> Number of objects in slab
@@ -94,6 +95,9 @@ 
 *   allocating a long series of objects that fill up slabs does not require

 *   the list lock.

 *

 *   For debug caches, all allocations are forced to go through a list_lock

 *   protected region to serialize against concurrent validation.

 *

 *   cpu_slab->lock local lock

 *

 *   This locks protect slowpath manipulation of all kmem_cache_cpu fields
@@ -4369,7 +4373,6 @@ static void list_slab_objects(struct kmem_cache *s, struct slab *slab, 
	void *p;



	slab_err(s, slab, text, s->name);

	slab_lock(slab, &flags);



	map = get_map(s, slab);

	for_each_object(p, s, addr, slab->objects) {
@@ -4380,7 +4383,6 @@ static void list_slab_objects(struct kmem_cache *s, struct slab *slab, 
		}

	}

	put_map(map);

	slab_unlock(slab, &flags);

#endif

}
@@ -5108,12 +5110,9 @@ static void validate_slab(struct kmem_cache *s, struct slab *slab, 
{

	void *p;

	void *addr = slab_address(slab);

	unsigned long flags;



	slab_lock(slab, &flags);



	if (!check_slab(s, slab) || !on_freelist(s, slab, NULL))

		goto unlock;

		return;



	/* Now we know that a valid freelist exists */

	__fill_map(obj_map, s, slab);
@@ -5124,8 +5123,6 @@ static void validate_slab(struct kmem_cache *s, struct slab *slab, 
		if (!check_object(s, slab, p, val))

			break;

	}

unlock:

	slab_unlock(slab, &flags);

}



static int validate_slab_node(struct kmem_cache *s,