[PATCH 1/4] mmzone: make holding lock_memory_hotplug() a requirement for updating pgdat size

[Cody P Schafer <cody@linux.vnet.ibm.com>]

All updaters of pgdat size (spanned_pages, start_pfn, and
present_pages) currently also hold lock_memory_hotplug() (in addition
to pgdat_resize_lock()).

Document this and make holding of that lock a requirement on the update
side for now, but keep the pgdat_resize_lock() around for readers that
can't lock a mutex.

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
---
 include/linux/mmzone.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 5c76737..09ac172 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -716,6 +716,9 @@ typedef struct pglist_data {
 	 * or node_spanned_pages stay constant.  Holding this will also
 	 * guarantee that any pfn_valid() stays that way.
 	 *
+	 * Updaters of any of these fields also must hold
+	 * lock_memory_hotplug().
+	 *
 	 * Nests above zone->lock and zone->size_seqlock.
 	 */
 	spinlock_t node_size_lock;
-- 
1.8.2.2

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