From: Peter Zijlstra <a.p.zijlstra@chello.nl> 
Subject: [PATCH 01/31] mm: serialize access to min_free_kbytes
Patch-mainline: not yet

There is a small race between the procfs caller and the memory hotplug caller
of setup_per_zone_wmarks(). Not a big deal, but the next patch will add yet
another caller. Time to close the gap.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Suresh Jayaraman <sjayaraman@suse.de>
---
 mm/page_alloc.c |   16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -148,6 +148,7 @@ static char * const zone_names[MAX_NR_ZO
 	 "Movable",
 };
 
+static DEFINE_SPINLOCK(min_free_lock);
 int min_free_kbytes = 1024;
 
 static unsigned long __meminitdata nr_kernel_pages;
@@ -4609,13 +4610,13 @@ static void setup_per_zone_lowmem_reserv
 }
 
 /**
- * setup_per_zone_wmarks - called when min_free_kbytes changes
+ * __setup_per_zone_wmarks - called when min_free_kbytes changes
  * or when memory is hot-{added|removed}
  *
  * Ensures that the watermark[min,low,high] values for each zone are set
  * correctly with respect to min_free_kbytes.
  */
-void setup_per_zone_wmarks(void)
+static void __setup_per_zone_wmarks(void)
 {
 	unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);
 	unsigned long lowmem_pages = 0;
@@ -4713,6 +4714,15 @@ static void __init setup_per_zone_inacti
 		calculate_zone_inactive_ratio(zone);
 }
 
+void setup_per_zone_wmarks(void)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&min_free_lock, flags);
+	__setup_per_zone_wmarks();
+	spin_unlock_irqrestore(&min_free_lock, flags);
+}
+
 /*
  * Initialise min_free_kbytes.
  *
@@ -4748,7 +4758,7 @@ static int __init init_per_zone_wmark_mi
 		min_free_kbytes = 128;
 	if (min_free_kbytes > 65536)
 		min_free_kbytes = 65536;
-	setup_per_zone_wmarks();
+	__setup_per_zone_wmarks();
 	setup_per_zone_lowmem_reserve();
 	setup_per_zone_inactive_ratio();
 	return 0;
