[RESEND -v2][PATCH 3/3] mem-hotplug: fix potential race while buildingzonelist for new populated zone

[Haicheng Li]

Christoph Lameter wrote:
> On Tue, 18 May 2010, Haicheng Li wrote:
>
> > +extern struct mutex zonelists_pageset_mutex;
>
> The mutext is used for multiple serializations having to do with zones.
> "pageset" suggests its only for pagesets.

hmm yes, "pageset" sounds a little bit confusing.

> So
>
> 	zones_mutex?
>
> or
>
> 	zonelists_mutex?

I prefer zonelists_mutex.

Christoph, how about below patch? Thanks.

---
From 3ccfd04d6ae9127bf0f5472db0b266e7b3f158bd Mon Sep 17 00:00:00 2001
From: Haicheng Li <haicheng.li@xxxxxxxxxxxxxxx>
Date: Wed, 19 May 2010 11:07:21 +0800
Subject: [PATCH] mem-hotplug: fix potential race while building zonelist for new populated zone

Add global mutex zonelists_mutex to fix the possible race:

    CPU0                                  CPU1                    CPU2
(1) zone->present_pages += online_pages;
(2)                                       build_all_zonelists();
(3)                                                               alloc_page();
(4)                                                               free_page();
(5) build_all_zonelists();
(6)   __build_all_zonelists();
(7)     zone->pageset = alloc_percpu();

In step (3,4), zone->pageset still points to boot_pageset, so bad
things may happen if 2+ nodes are in this state. Even if only 1 node
is accessing the boot_pageset, (3) may still consume too much memory
to fail the memory allocations in step (7).

Besides, atomic operation ensures alloc_percpu() in step (7) will never fail
since there is a new fresh memory block added in step(6).

Signed-off-by: Haicheng Li <haicheng.li@xxxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Reviewed-by: Andi Kleen <andi.kleen@xxxxxxxxx>
---
 include/linux/mmzone.h |    1 +
 mm/memory_hotplug.c    |   11 +++--------
 mm/page_alloc.c        |   15 ++++++++++++++-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index dbbcd50..4d87baa 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -641,6 +641,7 @@ typedef struct pglist_data {

 #include <linux/memory_hotplug.h>

+extern struct mutex zonelists_mutex;
 void get_zone_counts(unsigned long *active, unsigned long *inactive,
 			unsigned long *free);
 void build_all_zonelists(void *data);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index b564b6a..bc4a942 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -389,11 +389,6 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
 	int nid;
 	int ret;
 	struct memory_notify arg;
-	/*
-	 * mutex to protect zone->pageset when it's still shared
-	 * in onlined_pages()
-	 */
-	static DEFINE_MUTEX(zone_pageset_mutex);

 	arg.start_pfn = pfn;
 	arg.nr_pages = nr_pages;
@@ -420,14 +415,14 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
 	 * This means the page allocator ignores this zone.
 	 * So, zonelist must be updated after online.
 	 */
-	mutex_lock(&zone_pageset_mutex);
+	mutex_lock(&zonelists_mutex);
 	if (!populated_zone(zone))
 		need_zonelists_rebuild = 1;

 	ret = walk_system_ram_range(pfn, nr_pages, &onlined_pages,
 		online_pages_range);
 	if (ret) {
-		mutex_unlock(&zone_pageset_mutex);
+		mutex_unlock(&zonelists_mutex);
 		printk(KERN_DEBUG "online_pages %lx at %lx failed\n",
 			nr_pages, pfn);
 		memory_notify(MEM_CANCEL_ONLINE, &arg);
@@ -441,7 +436,7 @@ int online_pages(unsigned long pfn, unsigned long nr_pages)
 	else
 		zone_pcp_update(zone);

-	mutex_unlock(&zone_pageset_mutex);
+	mutex_unlock(&zonelists_mutex);
 	setup_per_zone_wmarks();
 	calculate_zone_inactive_ratio(zone);
 	if (onlined_pages) {
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 72c1211..c8e6146 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2434,8 +2434,11 @@ int numa_zonelist_order_handler(ctl_table *table, int write,
 			strncpy((char*)table->data, saved_string,
 				NUMA_ZONELIST_ORDER_LEN);
 			user_zonelist_order = oldval;
-		} else if (oldval != user_zonelist_order)
+		} else if (oldval != user_zonelist_order) {
+			mutex_lock(&zonelists_mutex);
 			build_all_zonelists(NULL);
+			mutex_unlock(&zonelists_mutex);
+		}
 	}
 out:
 	mutex_unlock(&zl_order_mutex);
@@ -2778,6 +2781,12 @@ static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch);
 static DEFINE_PER_CPU(struct per_cpu_pageset, boot_pageset);
 static void setup_zone_pageset(struct zone *zone);

+/*
+ * Global mutex to protect against size modification of zonelists
+ * as well as to serialize pageset setup for the new populated zone.
+ */
+DEFINE_MUTEX(zonelists_mutex);
+
 /* return values int ....just for stop_machine() */
 static __init_refok int __build_all_zonelists(void *data)
 {
@@ -2821,6 +2830,10 @@ static __init_refok int __build_all_zonelists(void *data)
 	return 0;
 }

+/*
+ * Called with zonelists_mutex held always
+ * unless system_state == SYSTEM_BOOTING.
+ */
 void build_all_zonelists(void *data)
 {
 	set_zonelist_order();
--
1.5.6.1




-haicheng
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