memory-hotplug: don't BUG() in register_memory_resource()

Out of memory condition is not a bug and while we can't add new memory
in such case crashing the system seems wrong.  Propagating the return
value from register_memory_resource() requires interface change.
Signed-off-by: NVitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: NIgor Mammedov <imammedo@redhat.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Xishi Qiu <qiuxishi@huawei.com>
Cc: Sheng Yong <shengyong1@huawei.com>
Cc: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -131,7 +131,8 @@ static struct resource *register_memory_resource(u64 start, u64 size)
 {
 	struct resource *res;
 	res = kzalloc(sizeof(struct resource), GFP_KERNEL);
-	BUG_ON(!res);
+	if (!res)
+		return ERR_PTR(-ENOMEM);
 
 	res->name = "System RAM";
 	res->start = start;
@@ -140,7 +141,7 @@ static struct resource *register_memory_resource(u64 start, u64 size)
 	if (request_resource(&iomem_resource, res) < 0) {
 		pr_debug("System RAM resource %pR cannot be added\n", res);
 		kfree(res);
-		res = NULL;
+		return ERR_PTR(-EEXIST);
 	}
 	return res;
 }
@@ -1312,8 +1313,8 @@ int __ref add_memory(int nid, u64 start, u64 size)
 	int ret;
 
 	res = register_memory_resource(start, size);
-	if (!res)
-		return -EEXIST;
+	if (IS_ERR(res))
+		return PTR_ERR(res);
 
 	ret = add_memory_resource(nid, res);
 	if (ret < 0)