From: Yasuaki Ishimatsu <isimatu.yasu...@jp.fujitsu.com>

If system supports memory hot-remove, online_pages() may online removed pages.
So online_pages() need to check whether onlining pages are present or not.

CC: David Rientjes <rient...@google.com>
CC: Jiang Liu <liu...@gmail.com>
CC: Len Brown <len.br...@intel.com>
CC: Benjamin Herrenschmidt <b...@kernel.crashing.org>
CC: Paul Mackerras <pau...@samba.org>
CC: Christoph Lameter <c...@linux.com>
Cc: Minchan Kim <minchan....@gmail.com>
CC: Andrew Morton <a...@linux-foundation.org>
CC: KOSAKI Motohiro <kosaki.motoh...@jp.fujitsu.com>
CC: Wen Congyang <we...@cn.fujitsu.com>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasu...@jp.fujitsu.com>
---
 include/linux/mmzone.h |   19 +++++++++++++++++++
 mm/memory_hotplug.c    |   13 +++++++++++++
 2 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 2daa54f..ac3ae30 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1180,6 +1180,25 @@ void sparse_init(void);
 #define sparse_index_init(_sec, _nid)  do {} while (0)
 #endif /* CONFIG_SPARSEMEM */
 
+#ifdef CONFIG_SPARSEMEM
+static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
+{
+       int i;
+       for (i = 0; i < nr_pages; i++) {
+               if (pfn_present(pfn + i))
+                       continue;
+               else
+                       return -EINVAL;
+       }
+       return 0;
+}
+#else
+static inline int pfns_present(unsigned long pfn, unsigned long nr_pages)
+{
+       return 0;
+}
+#endif /* CONFIG_SPARSEMEM*/
+
 #ifdef CONFIG_NODES_SPAN_OTHER_NODES
 bool early_pfn_in_nid(unsigned long pfn, int nid);
 #else
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 49f7747..299747d 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -467,6 +467,19 @@ int __ref online_pages(unsigned long pfn, unsigned long 
nr_pages)
        struct memory_notify arg;
 
        lock_memory_hotplug();
+       /*
+        * If system supports memory hot-remove, the memory may have been
+        * removed. So we check whether the memory has been removed or not.
+        *
+        * Note: When CONFIG_SPARSEMEM is defined, pfns_present() become
+        *       effective. If CONFIG_SPARSEMEM is not defined, pfns_present()
+        *       always returns 0.
+        */
+       ret = pfns_present(pfn, nr_pages);
+       if (ret) {
+               unlock_memory_hotplug();
+               return ret;
+       }
        arg.start_pfn = pfn;
        arg.nr_pages = nr_pages;
        arg.status_change_nid = -1;
-- 
1.7.1

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