mm/memory_hotplug.c: make add_memory_resource use __try_online_node

This is a small cleanup for the memhotplug code.  A lot more could be
done, but it is better to start somewhere.  I tried to unify/remove
duplicated code.

The following is what this patchset does:

1) add_memory_resource() has code to allocate a node in case it was
   offline.  Since try_online_node has some code for that as well, I just
   made add_memory_resource() to use that so we can remove duplicated
   code..  This is better explained in patch 1/4.

2) register_mem_sect_under_node() will be called only from
   link_mem_sections()

3) Make register_mem_sect_under_node() a callback of
   walk_memory_range()

4) Drop unnecessary checks from register_mem_sect_under_node()

I have done some tests and I could not see anything broken because of
this patchset.

add_memory_resource() contains code to allocate a new node in case it is
necessary.  Since try_online_node() also has some code for this purpose,
let us make use of that and remove duplicate code.

This introduces __try_online_node(), which is called by
add_memory_resource() and try_online_node().  __try_online_node() has
two new parameters, start_addr of the node, and if the node should be
onlined and registered right away.  This is always wanted if we are
calling from do_cpu_up(), but not when we are calling from memhotplug
code.  Nothing changes from the point of view of the users of
try_online_node(), since try_online_node passes start_addr=0 and
online_node=true to __try_online_node().

Link: http://lkml.kernel.org/r/20180622111839.10071-2-osalvador@techadventures.net
Signed-off-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Pavel Tatashin <pasha.tatashin@oracle.com>
Tested-by: Reza Arbab <arbab@linux.vnet.ibm.com>
Tested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Pasha Tatashin <Pavel.Tatashin@microsoft.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -1034,8 +1034,10 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 	return pgdat;
 }
 
-static void rollback_node_hotadd(int nid, pg_data_t *pgdat)
+static void rollback_node_hotadd(int nid)
 {
+	pg_data_t *pgdat = NODE_DATA(nid);
+
 	arch_refresh_nodedata(nid, NULL);
 	free_percpu(pgdat->per_cpu_nodestats);
 	arch_free_nodedata(pgdat);
@@ -1046,28 +1048,48 @@ static void rollback_node_hotadd(int nid, pg_data_t *pgdat)
 /**
  * try_online_node - online a node if offlined
  * @nid: the node ID
- *
+ * @start: start addr of the node
+ * @set_node_online: Whether we want to online the node
  * called by cpu_up() to online a node without onlined memory.
+ *
+ * Returns:
+ * 1 -> a new node has been allocated
+ * 0 -> the node is already online
+ * -ENOMEM -> the node could not be allocated
  */
-int try_online_node(int nid)
+static int __try_online_node(int nid, u64 start, bool set_node_online)
 {
-	pg_data_t	*pgdat;
-	int	ret;
+	pg_data_t *pgdat;
+	int ret = 1;
 
 	if (node_online(nid))
 		return 0;
 
-	mem_hotplug_begin();
-	pgdat = hotadd_new_pgdat(nid, 0);
+	pgdat = hotadd_new_pgdat(nid, start);
 	if (!pgdat) {
 		pr_err("Cannot online node %d due to NULL pgdat\n", nid);
 		ret = -ENOMEM;
 		goto out;
 	}
-	node_set_online(nid);
-	ret = register_one_node(nid);
-	BUG_ON(ret);
+
+	if (set_node_online) {
+		node_set_online(nid);
+		ret = register_one_node(nid);
+		BUG_ON(ret);
+	}
 out:
+	return ret;
+}
+
+/*
+ * Users of this function always want to online/register the node
+ */
+int try_online_node(int nid)
+{
+	int ret;
+
+	mem_hotplug_begin();
+	ret =  __try_online_node(nid, 0, true);
 	mem_hotplug_done();
 	return ret;
 }
@@ -1099,9 +1121,7 @@ static int online_memory_block(struct memory_block *mem, void *arg)
 int __ref add_memory_resource(int nid, struct resource *res, bool online)
 {
 	u64 start, size;
-	pg_data_t *pgdat = NULL;
-	bool new_pgdat;
-	bool new_node;
+	bool new_node = false;
 	int ret;
 
 	start = res->start;
@@ -1111,11 +1131,6 @@ int __ref add_memory_resource(int nid, struct resource *res, bool online)
 	if (ret)
 		return ret;
 
-	{	/* Stupid hack to suppress address-never-null warning */
-		void *p = NODE_DATA(nid);
-		new_pgdat = !p;
-	}
-
 	mem_hotplug_begin();
 
 	/*
@@ -1126,17 +1141,13 @@ int __ref add_memory_resource(int nid, struct resource *res, bool online)
 	 */
 	memblock_add_node(start, size, nid);
 
-	new_node = !node_online(nid);
-	if (new_node) {
-		pgdat = hotadd_new_pgdat(nid, start);
-		ret = -ENOMEM;
-		if (!pgdat)
-			goto error;
-	}
+	ret = __try_online_node(nid, start, false);
+	if (ret < 0)
+		goto error;
+	new_node = ret;
 
 	/* call arch's memory hotadd */
 	ret = arch_add_memory(nid, start, size, NULL, true);
-
 	if (ret < 0)
 		goto error;
 
@@ -1180,8 +1191,8 @@ register_fail:
 
 error:
 	/* rollback pgdat allocation and others */
-	if (new_pgdat && pgdat)
-		rollback_node_hotadd(nid, pgdat);
+	if (new_node)
+		rollback_node_hotadd(nid);
 	memblock_remove(start, size);
 
 out: