Merge tag 'slab-for-6.0-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab

Pull slab fix from Vlastimil Babka:

 - A fix from Waiman Long to avoid a theoretical deadlock reported by
   lockdep.

* tag 'slab-for-6.0-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/vbabka/slab:
  mm/slab_common: Deleting kobject in kmem_cache_destroy() without holding slab_mutex/cpu_hotplug_lock

Author: torvalds

mm/slab_common.c

@@ -392,6 +392,28 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align,
 }
 EXPORT_SYMBOL(kmem_cache_create);
 
+#ifdef SLAB_SUPPORTS_SYSFS
+/*
+ * For a given kmem_cache, kmem_cache_destroy() should only be called
+ * once or there will be a use-after-free problem. The actual deletion
+ * and release of the kobject does not need slab_mutex or cpu_hotplug_lock
+ * protection. So they are now done without holding those locks.
+ *
+ * Note that there will be a slight delay in the deletion of sysfs files
+ * if kmem_cache_release() is called indrectly from a work function.
+ */
+static void kmem_cache_release(struct kmem_cache *s)
+{
+	sysfs_slab_unlink(s);
+	sysfs_slab_release(s);
+}
+#else
+static void kmem_cache_release(struct kmem_cache *s)
+{
+	slab_kmem_cache_release(s);
+}
+#endif
+
 static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
 {
 	LIST_HEAD(to_destroy);
@@ -418,11 +440,7 @@ static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
 	list_for_each_entry_safe(s, s2, &to_destroy, list) {
 		debugfs_slab_release(s);
 		kfence_shutdown_cache(s);
-#ifdef SLAB_SUPPORTS_SYSFS
-		sysfs_slab_release(s);
-#else
-		slab_kmem_cache_release(s);
-#endif
+		kmem_cache_release(s);
 	}
 }
 
@@ -437,20 +455,11 @@ static int shutdown_cache(struct kmem_cache *s)
 	list_del(&s->list);
 
 	if (s->flags & SLAB_TYPESAFE_BY_RCU) {
-#ifdef SLAB_SUPPORTS_SYSFS
-		sysfs_slab_unlink(s);
-#endif
 		list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
 		schedule_work(&slab_caches_to_rcu_destroy_work);
 	} else {
 		kfence_shutdown_cache(s);
 		debugfs_slab_release(s);
-#ifdef SLAB_SUPPORTS_SYSFS
-		sysfs_slab_unlink(s);
-		sysfs_slab_release(s);
-#else
-		slab_kmem_cache_release(s);
-#endif
 	}
 
 	return 0;
@@ -465,14 +474,16 @@ void slab_kmem_cache_release(struct kmem_cache *s)
 
 void kmem_cache_destroy(struct kmem_cache *s)
 {
+	int refcnt;
+
 	if (unlikely(!s) || !kasan_check_byte(s))
 		return;
 
 	cpus_read_lock();
 	mutex_lock(&slab_mutex);
 
-	s->refcount--;
-	if (s->refcount)
+	refcnt = --s->refcount;
+	if (refcnt)
 		goto out_unlock;
 
 	WARN(shutdown_cache(s),
@@ -481,6 +492,8 @@ void kmem_cache_destroy(struct kmem_cache *s)
 out_unlock:
 	mutex_unlock(&slab_mutex);
 	cpus_read_unlock();
+	if (!refcnt && !(s->flags & SLAB_TYPESAFE_BY_RCU))
+		kmem_cache_release(s);
 }
 EXPORT_SYMBOL(kmem_cache_destroy);