mm/memory_hotplug.c: call register_mem_sect_under_node()

When hotplugging memory, it is possible that two calls are being made to
register_mem_sect_under_node().

One comes from __add_section()->hotplug_memory_register() and the other
from add_memory_resource()->link_mem_sections() if we had to register a
new node.

In case we had to register a new node, hotplug_memory_register() will
only handle/allocate the memory_block's since
register_mem_sect_under_node() will return right away because the node
it is not online yet.

I think it is better if we leave hotplug_memory_register() to
handle/allocate only memory_block's and make link_mem_sections() to call
register_mem_sect_under_node().

So this patch removes the call to register_mem_sect_under_node() from
hotplug_memory_register(), and moves the call to link_mem_sections() out
of the condition, so it will always be called.  In this way we only have
one place where the memory sections are registered.

Link: http://lkml.kernel.org/r/20180622111839.10071-3-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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/base/memory.c

@@ -736,8 +736,6 @@ int hotplug_memory_register(int nid, struct mem_section *section)
 		mem->section_count++;
 	}
 
-	if (mem->section_count == sections_per_block)
-		ret = register_mem_sect_under_node(mem, nid, false);
 out:
 	mutex_unlock(&mem_sysfs_mutex);
 	return ret;

mm/memory_hotplug.c

@@ -1123,6 +1123,7 @@ int __ref add_memory_resource(int nid, struct resource *res, bool online)
 	u64 start, size;
 	bool new_node = false;
 	int ret;
+	unsigned long start_pfn, nr_pages;
 
 	start = res->start;
 	size = resource_size(res);
@@ -1151,34 +1152,23 @@ int __ref add_memory_resource(int nid, struct resource *res, bool online)
 	if (ret < 0)
 		goto error;
 
-	/* we online node here. we can't roll back from here. */
-	node_set_online(nid);
-
 	if (new_node) {
-		unsigned long start_pfn = start >> PAGE_SHIFT;
-		unsigned long nr_pages = size >> PAGE_SHIFT;
-
-		ret = __register_one_node(nid);
-		if (ret)
-			goto register_fail;
-
-		/*
-		 * link memory sections under this node. This is already
-		 * done when creatig memory section in register_new_memory
-		 * but that depends to have the node registered so offline
-		 * nodes have to go through register_node.
-		 * TODO clean up this mess.
-		 */
-		ret = link_mem_sections(nid, start_pfn, nr_pages, false);
-register_fail:
-		/*
-		 * If sysfs file of new node can't create, cpu on the node
+		/* If sysfs file of new node can't be created, cpu on the node
 		 * can't be hot-added. There is no rollback way now.
 		 * So, check by BUG_ON() to catch it reluctantly..
+		 * We online node here. We can't roll back from here.
 		 */
+		node_set_online(nid);
+		ret = __register_one_node(nid);
 		BUG_ON(ret);
 	}
 
+	/* link memory sections under this node.*/
+	start_pfn = start >> PAGE_SHIFT;
+	nr_pages = size >> PAGE_SHIFT;
+	ret = link_mem_sections(nid, start_pfn, nr_pages, false);
+	BUG_ON(ret);
+
 	/* create new memmap entry */
 	firmware_map_add_hotplug(start, start + size, "System RAM");