mm/slab: restructure kmem_cache_create() debug checks

kmem_cache_create() does cache integrity checks when CONFIG_DEBUG_VM is
defined.  These checks interspersed with the regular code path has lead
to compile time warnings when compiled without CONFIG_DEBUG_VM defined.
Restructuring the code to move the integrity checks in to a new function
would eliminate the current compile warning problem and also will allow
for future changes to the debug only code to evolve without introducing
new warnings in the regular path.

This restructuring work is based on the discussion in the following
thread:

https://lkml.org/lkml/2012/7/13/424

[akpm@linux-foundation.org: fix build, cleanup]
Signed-off-by: Shuah Khan <shuah.khan@hp.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slab_common.c

@@ -23,6 +23,52 @@ enum slab_state slab_state;
 LIST_HEAD(slab_caches);
 DEFINE_MUTEX(slab_mutex);
 
+#ifdef CONFIG_DEBUG_VM
+static int kmem_cache_sanity_check(const char *name, size_t size)
+{
+	struct kmem_cache *s = NULL;
+
+	if (!name || in_interrupt() || size < sizeof(void *) ||
+		size > KMALLOC_MAX_SIZE) {
+		pr_err("kmem_cache_create(%s) integrity check failed\n", name);
+		return -EINVAL;
+	}
+
+	list_for_each_entry(s, &slab_caches, list) {
+		char tmp;
+		int res;
+
+		/*
+		 * This happens when the module gets unloaded and doesn't
+		 * destroy its slab cache and no-one else reuses the vmalloc
+		 * area of the module.  Print a warning.
+		 */
+		res = probe_kernel_address(s->name, tmp);
+		if (res) {
+			pr_err("Slab cache with size %d has lost its name\n",
+			       s->object_size);
+			continue;
+		}
+
+		if (!strcmp(s->name, name)) {
+			pr_err("%s (%s): Cache name already exists.\n",
+			       __func__, name);
+			dump_stack();
+			s = NULL;
+			return -EINVAL;
+		}
+	}
+
+	WARN_ON(strchr(name, ' '));	/* It confuses parsers */
+	return 0;
+}
+#else
+static inline int kmem_cache_sanity_check(const char *name, size_t size)
+{
+	return 0;
+}
+#endif
+
 /*
  * kmem_cache_create - Create a cache.
  * @name: A string which is used in /proc/slabinfo to identify this cache.
@@ -53,60 +99,13 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
 {
 	struct kmem_cache *s = NULL;
 
-#ifdef CONFIG_DEBUG_VM
-	if (!name || in_interrupt() || size < sizeof(void *) ||
-		size > KMALLOC_MAX_SIZE) {
-		printk(KERN_ERR "kmem_cache_create(%s) integrity check"
-			" failed\n", name);
-		goto out;
-	}
-#endif
-
 	get_online_cpus();
 	mutex_lock(&slab_mutex);
-
-#ifdef CONFIG_DEBUG_VM
-	list_for_each_entry(s, &slab_caches, list) {
-		char tmp;
-		int res;
-
-		/*
-		 * This happens when the module gets unloaded and doesn't
-		 * destroy its slab cache and no-one else reuses the vmalloc
-		 * area of the module.  Print a warning.
-		 */
-		res = probe_kernel_address(s->name, tmp);
-		if (res) {
-			printk(KERN_ERR
-			       "Slab cache with size %d has lost its name\n",
-			       s->object_size);
-			continue;
-		}
-
-		if (!strcmp(s->name, name)) {
-			printk(KERN_ERR "kmem_cache_create(%s): Cache name"
-				" already exists.\n",
-				name);
-			dump_stack();
-			s = NULL;
-			goto oops;
-		}
-	}
-
-	WARN_ON(strchr(name, ' '));	/* It confuses parsers */
-#endif
-
+	if (kmem_cache_sanity_check(name, size) == 0)
 		s = __kmem_cache_create(name, size, align, flags, ctor);
-
-#ifdef CONFIG_DEBUG_VM
-oops:
-#endif
 	mutex_unlock(&slab_mutex);
 	put_online_cpus();
 
-#ifdef CONFIG_DEBUG_VM
-out:
-#endif
 	if (!s && (flags & SLAB_PANIC))
 		panic("kmem_cache_create: Failed to create slab '%s'\n", name);