[PATCH 1/10] memory-hotplug : check whether memory is offline or not when removing memory

[Yasuaki Ishimatsu]

When calling remove_memory(), the memory should be offline. If the function
is used to online memory, kernel panic may occur.

So the patch checks whether memory is offline or not.

CC: David Rientjes <rientjes at google.com>
CC: Jiang Liu <liuj97 at gmail.com>
CC: Len Brown <len.brown at intel.com>
CC: Christoph Lameter <cl at linux.com>
Cc: Minchan Kim <minchan.kim at gmail.com>
CC: Andrew Morton <akpm at linux-foundation.org>
CC: KOSAKI Motohiro <kosaki.motohiro at jp.fujitsu.com> 
Signed-off-by: Wen Congyang <wency at cn.fujitsu.com>
Signed-off-by: Yasuaki Ishimatsu <isimatu.yasuaki at jp.fujitsu.com>

---
 drivers/base/memory.c  |   39 +++++++++++++++++++++++++++++++++++++++
 include/linux/memory.h |    5 +++++
 mm/memory_hotplug.c    |   17 +++++++++++++++--
 3 files changed, 59 insertions(+), 2 deletions(-)

Index: linux-3.6/drivers/base/memory.c
===================================================================
--- linux-3.6.orig/drivers/base/memory.c	2012-10-04 14:22:57.000000000 +0900
+++ linux-3.6/drivers/base/memory.c	2012-10-04 14:45:46.653585860 +0900
@@ -70,6 +70,45 @@ void unregister_memory_isolate_notifier(
 }
 EXPORT_SYMBOL(unregister_memory_isolate_notifier);
 
+bool is_memblk_offline(unsigned long start, unsigned long size)
+{
+	struct memory_block *mem = NULL;
+	struct mem_section *section;
+	unsigned long start_pfn, end_pfn;
+	unsigned long pfn, section_nr;
+
+	start_pfn = PFN_DOWN(start);
+	end_pfn = PFN_UP(start + size);
+
+	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+		section_nr = pfn_to_section_nr(pfn);
+		if (!present_section_nr(section_nr))
+			continue;
+
+		section = __nr_to_section(section_nr);
+		/* same memblock? */
+		if (mem)
+			if ((section_nr >= mem->start_section_nr) &&
+			    (section_nr <= mem->end_section_nr))
+				continue;
+
+		mem = find_memory_block_hinted(section, mem);
+		if (!mem)
+			continue;
+		if (mem->state == MEM_OFFLINE)
+			continue;
+
+		kobject_put(&mem->dev.kobj);
+		return false;
+	}
+
+	if (mem)
+		kobject_put(&mem->dev.kobj);
+
+	return true;
+}
+EXPORT_SYMBOL(is_memblk_offline);
+
 /*
  * register_memory - Setup a sysfs device for a memory block
  */
Index: linux-3.6/include/linux/memory.h
===================================================================
--- linux-3.6.orig/include/linux/memory.h	2012-10-02 18:00:22.000000000 +0900
+++ linux-3.6/include/linux/memory.h	2012-10-04 14:44:40.902581028 +0900
@@ -106,6 +106,10 @@ static inline int memory_isolate_notify(
 {
 	return 0;
 }
+static inline bool is_memblk_offline(unsigned long start, unsigned long size)
+{
+	return false;
+}
 #else
 extern int register_memory_notifier(struct notifier_block *nb);
 extern void unregister_memory_notifier(struct notifier_block *nb);
@@ -120,6 +124,7 @@ extern int memory_isolate_notify(unsigne
 extern struct memory_block *find_memory_block_hinted(struct mem_section *,
 							struct memory_block *);
 extern struct memory_block *find_memory_block(struct mem_section *);
+extern bool is_memblk_offline(unsigned long start, unsigned long size);
 #define CONFIG_MEM_BLOCK_SIZE	(PAGES_PER_SECTION<<PAGE_SHIFT)
 enum mem_add_context { BOOT, HOTPLUG };
 #endif /* CONFIG_MEMORY_HOTPLUG_SPARSE */
Index: linux-3.6/mm/memory_hotplug.c
===================================================================
--- linux-3.6.orig/mm/memory_hotplug.c	2012-10-04 14:31:08.000000000 +0900
+++ linux-3.6/mm/memory_hotplug.c	2012-10-04 14:58:22.449687986 +0900
@@ -1045,8 +1045,21 @@ int offline_memory(u64 start, u64 size)
 
 int remove_memory(int nid, u64 start, u64 size)
 {
-	/* It is not implemented yet*/
-	return 0;
+	int ret = 0;
+	lock_memory_hotplug();
+	/*
+	 * The memory might become online by other task, even if you offine it.
+	 * So we check whether the memory has been onlined or not.
+	 */
+	if (!is_memblk_offline(start, size)) {
+		pr_warn("memory removing [mem %#010llx-%#010llx] failed, "
+			"because the memmory range is online\n",
+			start, start + size);
+		ret = -EAGAIN;
+	}
+
+	unlock_memory_hotplug();
+	return ret;
 }
 EXPORT_SYMBOL_GPL(remove_memory);
 #else