2 files changed, 10 insertions, 0 deletions

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 31c237a00c48..12b9eb5a36c3 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -161,6 +161,12 @@ extern void register_page_bootmem_info_node(struct pglist_data *pgdat);
 extern void put_page_bootmem(struct page *page);
 #endif
 
+/*
+ * Lock for memory hotplug guarantees 1) all callbacks for memory hotplug
+ * notifier will be called under this. 2) offline/online/add/remove memory
+ * will not run simultaneously.
+ */
+
 void lock_memory_hotplug(void);
 void unlock_memory_hotplug(void);
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 2c6523af5473..83163c096a75 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -407,6 +407,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
         int ret;
         struct memory_notify arg;
 
+        lock_memory_hotplug();
         arg.start_pfn = pfn;
         arg.nr_pages = nr_pages;
         arg.status_change_nid = -1;
@@ -419,6 +420,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
         ret = notifier_to_errno(ret);
         if (ret) {
                 memory_notify(MEM_CANCEL_ONLINE, &arg);
+                unlock_memory_hotplug();
                 return ret;
         }
         /*
@@ -443,6 +445,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
                 printk(KERN_DEBUG "online_pages %lx at %lx failed\n",
                         nr_pages, pfn);
                 memory_notify(MEM_CANCEL_ONLINE, &arg);
+                unlock_memory_hotplug();
                 return ret;
         }
 
@@ -467,6 +470,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
 
         if (onlined_pages)
                 memory_notify(MEM_ONLINE, &arg);
+        unlock_memory_hotplug();
 
         return 0;
 }