mm/slab_common: Improve error handling in kmem_cache_create

Instead of using s == NULL use an errorcode. This allows much more
detailed diagnostics as to what went wrong. As we add more functionality
from the slab allocators to the common kmem_cache_create() function we will
also add more error conditions.

Print the error code during the panic as well as in a warning if the module
can handle failure. The API for kmem_cache_create() currently does not allow
the returning of an error code. Return NULL but log the cause of the problem
in the syslog.
Reviewed-by: NGlauber Costa <glommer@parallels.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Signed-off-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NPekka Enberg <penberg@kernel.org>

mm/slab_common.c

@@ -98,16 +98,36 @@ struct kmem_cache *kmem_cache_create(const char *name, size_t size, size_t align
 		unsigned long flags, void (*ctor)(void *))
 {
 	struct kmem_cache *s = NULL;
+	int err = 0;
 
 	get_online_cpus();
 	mutex_lock(&slab_mutex);
-	if (kmem_cache_sanity_check(name, size) == 0)
-		s = __kmem_cache_create(name, size, align, flags, ctor);
+
+	if (!kmem_cache_sanity_check(name, size) == 0)
+		goto out_locked;
+
+
+	s = __kmem_cache_create(name, size, align, flags, ctor);
+	if (!s)
+		err = -ENOSYS; /* Until __kmem_cache_create returns code */
+
+out_locked:
 	mutex_unlock(&slab_mutex);
 	put_online_cpus();
 
-	if (!s && (flags & SLAB_PANIC))
-		panic("kmem_cache_create: Failed to create slab '%s'\n", name);
+	if (err) {
+
+		if (flags & SLAB_PANIC)
+			panic("kmem_cache_create: Failed to create slab '%s'. Error %d\n",
+				name, err);
+		else {
+			printk(KERN_WARNING "kmem_cache_create(%s) failed with error %d",
+				name, err);
+			dump_stack();
+		}
+
+		return NULL;
+	}
 
 	return s;
 }