[PATCH 2/3] mm/memory_hotplug: harden try_offline_node against bogus nid

[Jia He]

When testing the remove_memory path of dax pmem, there will be a panic with
call trace:
  try_remove_memory+0x84/0x170
  remove_memory+0x38/0x58
  dev_dax_kmem_remove+0x3c/0x84 [kmem]
  device_release_driver_internal+0xfc/0x1c8
  device_release_driver+0x28/0x38
  bus_remove_device+0xd4/0x158
  device_del+0x160/0x3a0
  unregister_dev_dax+0x30/0x68
  devm_action_release+0x20/0x30
  release_nodes+0x150/0x240
  devres_release_all+0x6c/0x1d0
  device_release_driver_internal+0x10c/0x1c8
  driver_detach+0xac/0x170
  bus_remove_driver+0x64/0x130
  driver_unregister+0x34/0x60
  dax_pmem_exit+0x14/0xffc4 [dax_pmem]
  __arm64_sys_delete_module+0x18c/0x2d0
  el0_svc_common.constprop.2+0x78/0x168
  do_el0_svc+0x34/0xa0
  el0_sync_handler+0xe0/0x188
  el0_sync+0x164/0x180

It is caused by the bogus nid (-1). Although the root cause is pmem dax
translates from pxm to node_id incorrectly due to numa_off, it is worth
hardening the codes in try_offline_node(), quiting if !pgdat.

Signed-off-by: Jia He <justin.he at arm.com>
---
 mm/memory_hotplug.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index da374cd3d45b..e1e290577b45 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1680,6 +1680,9 @@ void try_offline_node(int nid)
 	pg_data_t *pgdat = NODE_DATA(nid);
 	int rc;
 
+	if (WARN_ON(!pgdat))
+		return;
+
 	/*
 	 * If the node still spans pages (especially ZONE_DEVICE), don't
 	 * offline it. A node spans memory after move_pfn_range_to_zone(),
-- 
2.17.1