memory hotplug: one more lock on memory hotplug

Now, memory_hotplug_(un)lock() is used for add/remove/offline pages
for avoiding races with hibernation. But this should be held in
online_pages(), too. It seems asymmetric.

There are cases where one has to avoid a race with memory hotplug
notifier and his own local code, and hotplug v.s. hotplug.
This will add a generic solution for avoiding races. In other view,
having lock here has no big impacts. online pages is tend to be
done by udev script at el against each memory section one by one.

Then, it's better to have lock here, too.

Cc: <stable@kernel.org> # 2.6.37
Reviewed-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 31c237a00c48e472b7c8e6c435fe66de9b0e232a..12b9eb5a36c311474c9caf077d96e4f4d31c8163 100644 (file)
--- 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 2c6523af54738faba3dd37eef938315503275de4..83163c096a7580645b6b281257fb3128cde93bc2 100644 (file)
--- 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;
 }