memory-hotplug: clear pgdat which is allocated by bootmem in try_offline_node()

When hot adding the same memory after hot removal, the following
messages are shown:

  WARNING: CPU: 20 PID: 6 at mm/page_alloc.c:4968 free_area_init_node+0x3fe/0x426()
  ...
  Call Trace:
    dump_stack+0x46/0x58
    warn_slowpath_common+0x81/0xa0
    warn_slowpath_null+0x1a/0x20
    free_area_init_node+0x3fe/0x426
    hotadd_new_pgdat+0x90/0x110
    add_memory+0xd4/0x200
    acpi_memory_device_add+0x1aa/0x289
    acpi_bus_attach+0xfd/0x204
    acpi_bus_attach+0x178/0x204
    acpi_bus_scan+0x6a/0x90
    acpi_device_hotplug+0xe8/0x418
    acpi_hotplug_work_fn+0x1f/0x2b
    process_one_work+0x14e/0x3f0
    worker_thread+0x11b/0x510
    kthread+0xe1/0x100
    ret_from_fork+0x7c/0xb0

The detaled explanation is as follows:

When hot removing memory, pgdat is set to 0 in try_offline_node().  But
if the pgdat is allocated by bootmem allocator, the clearing step is
skipped.

And when hot adding the same memory, the uninitialized pgdat is reused.
But free_area_init_node() checks wether pgdat is set to zero.  As a
result, free_area_init_node() hits WARN_ON().

This patch clears pgdat which is allocated by bootmem allocator in
try_offline_node().

Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Zhang Zhen <zhenzhang.zhang@huawei.com>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Tang Chen <tangchen@cn.fujitsu.com>
Reviewed-by: Toshi Kani <toshi.kani@hp.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memory_hotplug.c

@@ -1912,7 +1912,6 @@ void try_offline_node(int nid)
 	unsigned long start_pfn = pgdat->node_start_pfn;
 	unsigned long end_pfn = start_pfn + pgdat->node_spanned_pages;
 	unsigned long pfn;
-	struct page *pgdat_page = virt_to_page(pgdat);
 	int i;
 
 	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
@@ -1941,10 +1940,6 @@ void try_offline_node(int nid)
 	node_set_offline(nid);
 	unregister_one_node(nid);
 
-	if (!PageSlab(pgdat_page) && !PageCompound(pgdat_page))
-		/* node data is allocated from boot memory */
-		return;
-
 	/* free waittable in each zone */
 	for (i = 0; i < MAX_NR_ZONES; i++) {
 		struct zone *zone = pgdat->node_zones + i;