slub: Allow removal of slab caches during boot

Serialize kmem_cache_create and kmem_cache_destroy using the slub_lock. Only
possible after the use of the slub_lock during dynamic dma creation has been
removed.

Then make sure that the setup of the slab sysfs entries does not race
with kmem_cache_create and kmem_cache destroy.

If a slab cache is removed before we have setup sysfs then simply skip over
the sysfs handling.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Roland Dreier <rdreier@cisco.com>
Signed-off-by: Christoph Lameter <cl@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi>

mm/slub.c

@@ -2491,7 +2491,6 @@ void kmem_cache_destroy(struct kmem_cache *s)
 	s->refcount--;
 	if (!s->refcount) {
 		list_del(&s->list);
-		up_write(&slub_lock);
 		if (kmem_cache_close(s)) {
 			printk(KERN_ERR "SLUB %s: %s called for cache that "
 				"still has objects.\n", s->name, __func__);
@@ -2500,8 +2499,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
 		if (s->flags & SLAB_DESTROY_BY_RCU)
 			rcu_barrier();
 		sysfs_slab_remove(s);
-	} else
-		up_write(&slub_lock);
+	}
+	up_write(&slub_lock);
 }
 EXPORT_SYMBOL(kmem_cache_destroy);
 
@@ -3227,14 +3226,12 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 		 */
 		s->objsize = max(s->objsize, (int)size);
 		s->inuse = max_t(int, s->inuse, ALIGN(size, sizeof(void *)));
-		up_write(&slub_lock);
 
 		if (sysfs_slab_alias(s, name)) {
-			down_write(&slub_lock);
 			s->refcount--;
-			up_write(&slub_lock);
 			goto err;
 		}
+		up_write(&slub_lock);
 		return s;
 	}
 
@@ -3243,14 +3240,12 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size,
 		if (kmem_cache_open(s, GFP_KERNEL, name,
 				size, align, flags, ctor)) {
 			list_add(&s->list, &slab_caches);
-			up_write(&slub_lock);
 			if (sysfs_slab_add(s)) {
-				down_write(&slub_lock);
 				list_del(&s->list);
-				up_write(&slub_lock);
 				kfree(s);
 				goto err;
 			}
+			up_write(&slub_lock);
 			return s;
 		}
 		kfree(s);
@@ -4498,6 +4493,13 @@ static int sysfs_slab_add(struct kmem_cache *s)
 
 static void sysfs_slab_remove(struct kmem_cache *s)
 {
+	if (slab_state < SYSFS)
+		/*
+		 * Sysfs has not been setup yet so no need to remove the
+		 * cache from sysfs.
+		 */
+		return;
+
 	kobject_uevent(&s->kobj, KOBJ_REMOVE);
 	kobject_del(&s->kobj);
 	kobject_put(&s->kobj);
@@ -4543,8 +4545,11 @@ static int __init slab_sysfs_init(void)
 	struct kmem_cache *s;
 	int err;
 
+	down_write(&slub_lock);
+
 	slab_kset = kset_create_and_add("slab", &slab_uevent_ops, kernel_kobj);
 	if (!slab_kset) {
+		up_write(&slub_lock);
 		printk(KERN_ERR "Cannot register slab subsystem.\n");
 		return -ENOSYS;
 	}
@@ -4569,6 +4574,7 @@ static int __init slab_sysfs_init(void)
 		kfree(al);
 	}
 
+	up_write(&slub_lock);
 	resiliency_test();
 	return 0;
 }