mm, hotplug: protect zonelist building with zonelists_mutex

Commit 959ecc48fc75 ("mm/memory_hotplug.c: fix building of node hotplug
zonelist") does not protect the build_all_zonelists() call with
zonelists_mutex as needed.  This can lead to races in constructing
zonelist ordering if a concurrent build is underway.  Protecting this
with lock_memory_hotplug() is insufficient since zonelists can be
rebuild though sysfs as well.

Signed-off-by: David Rientjes <rientjes@google.com>
Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 78dba9f04b5b..c46887b5a11e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -498,7 +498,9 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
          * The node we allocated has no zone fallback lists. For avoiding
          * to access not-initialized zonelist, build here.
          */
+        mutex_lock(&zonelists_mutex);
         build_all_zonelists(NULL);
+        mutex_unlock(&zonelists_mutex);
 
         return pgdat;
 }