cpu/mem hotplug: add try_online_node() for cpu_up()

cpu_up() has #ifdef CONFIG_MEMORY_HOTPLUG code blocks, which call
mem_online_node() to put its node online if offlined and then call
build_all_zonelists() to initialize the zone list.

These steps are specific to memory hotplug, and should be managed in
mm/memory_hotplug.c.  lock_memory_hotplug() should also be held for the
whole steps.

For this reason, this patch replaces mem_online_node() with
try_online_node(), which performs the whole steps with
lock_memory_hotplug() held.  try_online_node() is named after
try_offline_node() as they have similar purpose.

There is no functional change in this patch.

Signed-off-by: Toshi Kani <toshi.kani@hp.com>
Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 24 insertions, 29 deletions

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index dd38e62b84d2..22203c293f07 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -94,6 +94,8 @@ extern void __online_page_set_limits(struct page *page);
 extern void __online_page_increment_counters(struct page *page);
 extern void __online_page_free(struct page *page);
 
+extern int try_online_node(int nid);
+
 #ifdef CONFIG_MEMORY_HOTREMOVE
 extern bool is_pageblock_removable_nolock(struct page *page);
 extern int arch_remove_memory(u64 start, u64 size);
@@ -225,6 +227,11 @@ static inline void register_page_bootmem_info_node(struct pglist_data *pgdat)
 {
 }
 
+static inline int try_online_node(int nid)
+{
+        return 0;
+}
+
 static inline void lock_memory_hotplug(void) {}
 static inline void unlock_memory_hotplug(void) {}
 
@@ -256,7 +263,6 @@ static inline void remove_memory(int nid, u64 start, u64 size) {}
 
 extern int walk_memory_range(unsigned long start_pfn, unsigned long end_pfn,
                 void *arg, int (*func)(struct memory_block *, void *));
-extern int mem_online_node(int nid);
 extern int add_memory(int nid, u64 start, u64 size);
 extern int arch_add_memory(int nid, u64 start, u64 size);
 extern int offline_pages(unsigned long start_pfn, unsigned long nr_pages);
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 63aa50d7ce1e..973d034acf84 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -437,11 +437,6 @@ int cpu_up(unsigned int cpu)
 {
         int err = 0;
 
-#ifdef  CONFIG_MEMORY_HOTPLUG
-        int nid;
-        pg_data_t       *pgdat;
-#endif
-
         if (!cpu_possible(cpu)) {
                 printk(KERN_ERR "can't online cpu %d because it is not "
                         "configured as may-hotadd at boot time\n", cpu);
@@ -452,27 +447,9 @@ int cpu_up(unsigned int cpu)
                 return -EINVAL;
         }
 
-#ifdef  CONFIG_MEMORY_HOTPLUG
-        nid = cpu_to_node(cpu);
-        if (!node_online(nid)) {
-                err = mem_online_node(nid);
-                if (err)
-                        return err;
-        }
-
-        pgdat = NODE_DATA(nid);
-        if (!pgdat) {
-                printk(KERN_ERR
-                        "Can't online cpu %d due to NULL pgdat\n", cpu);
-                return -ENOMEM;
-        }
-
-        if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
-                mutex_lock(&zonelists_mutex);
-                build_all_zonelists(NULL, NULL);
-                mutex_unlock(&zonelists_mutex);
-        }
-#endif
+        err = try_online_node(cpu_to_node(cpu));
+        if (err)
+                return err;
 
         cpu_maps_update_begin();
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 5118028468eb..8285346be663 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1043,17 +1043,23 @@ static void rollback_node_hotadd(int nid, pg_data_t *pgdat)
 }
 
 
-/*
+/**
+ * try_online_node - online a node if offlined
+ *
  * called by cpu_up() to online a node without onlined memory.
  */
-int mem_online_node(int nid)
+int try_online_node(int nid)
 {
         pg_data_t       *pgdat;
         int     ret;
 
+        if (node_online(nid))
+                return 0;
+
         lock_memory_hotplug();
         pgdat = hotadd_new_pgdat(nid, 0);
         if (!pgdat) {
+                pr_err("Cannot online node %d due to NULL pgdat\n", nid);
                 ret = -ENOMEM;
                 goto out;
         }
@@ -1061,6 +1067,12 @@ int mem_online_node(int nid)
         ret = register_one_node(nid);
         BUG_ON(ret);
 
+        if (pgdat->node_zonelists->_zonerefs->zone == NULL) {
+                mutex_lock(&zonelists_mutex);
+                build_all_zonelists(NULL, NULL);
+                mutex_unlock(&zonelists_mutex);
+        }
+
 out:
         unlock_memory_hotplug();
         return ret;