linux-kernel - [PATCH 2/2] mem-hotplug: Fix wrong check for zone->pageset initialization in online

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Date:	Fri, 31 Oct 2014 17:46:52 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	<akpm@...ux-foundation.org>, <santosh.shilimkar@...com>,
	<grygorii.strashko@...com>, <yinghai@...nel.org>,
	<isimatu.yasuaki@...fujitsu.co>, <fabf@...net.be>,
	<nzimmer@....com>, <wangnan0@...wei.com>, <vdavydov@...allels.com>,
	<toshi.kani@...com>, <phacht@...ux.vnet.ibm.com>, <tj@...nel.org>,
	<kirill.shutemov@...ux.intel.com>, <riel@...hat.com>,
	<luto@...capital.net>, <hpa@...ux.intel.com>,
	<aarcange@...hat.com>, <qiuxishi@...wei.com>, <mgorman@...e.de>,
	<rientjes@...gle.com>, <hannes@...xchg.org>
CC:	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	<tangchen@...fujitsu.com>, Gu Zheng <guz.fnst@...fujitsu.com>
Subject: [PATCH 2/2] mem-hotplug: Fix wrong check for zone->pageset initialization in online_pages().

When we are doing memory hot-add, the following functions are called:

add_memory()
|--> hotadd_new_pgdat()
     |--> free_area_init_node()
          |--> free_area_init_core()
               |--> zone->present_pages = realsize;           /* 1. zone is populated */
                    |--> zone_pcp_init()
                         |--> zone->pageset = &boot_pageset;  /* 2. zone->pageset is set to boot_pageset */

There are two problems here:
1. Zones could be populated before any memory is onlined.
2. All the zones on a newly added node have the same pageset pointing to boot_pageset.

The above two problems will result in the following problem:
When we online memory on one node, e.g node2, the following code is executed:

online_pages()
{
        ......
        if (!populated_zone(zone)) {
                need_zonelists_rebuild = 1;
                build_all_zonelists(NULL, zone);
        }
        ......
}

Because of problem 1, the zone has been populated, and the build_all_zonelists()
                      will never called. zone->pageset won't be updated.
Because of problem 2, All the zones on a newly added node have the same pageset
                      pointing to boot_pageset.
And as a result, when we online memory on node2, node3's meminfo will corrupt.
Pages on node2 may be freed to node3.

# for ((i = 2048; i < 2064; i++)); do echo online_movable > /sys/devices/system/node/node2/memory$i/state; done
# cat /sys/devices/system/node/node2/meminfo
Node 2 MemTotal:       33554432 kB
Node 2 MemFree:        33549092 kB
Node 2 MemUsed:            5340 kB
......
# cat /sys/devices/system/node/node3/meminfo
Node 3 MemTotal:              0 kB
Node 3 MemFree:               248 kB                    /* corrupted */
Node 3 MemUsed:               0 kB
......

We have to populate some zones before onlining memory, otherwise no memory could be onlined.
So when onlining pages, we should also check if zone->pageset is pointing to boot_pageset.

Signed-off-by: Gu Zheng <guz.fnst@...fujitsu.com>
Signed-off-by: Tang Chen <tangchen@...fujitsu.com>
---
 include/linux/mm.h  | 1 +
 mm/memory_hotplug.c | 6 +++++-
 mm/page_alloc.c     | 5 +++++
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 02d11ee..83e6505 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1732,6 +1732,7 @@ void warn_alloc_failed(gfp_t gfp_mask, int order, const char *fmt, ...);
 
 extern void setup_per_cpu_pageset(void);
 
+extern bool zone_pcp_initialized(struct zone *zone);
 extern void zone_pcp_update(struct zone *zone);
 extern void zone_pcp_reset(struct zone *zone);
 
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 3ab01b2..bc0de0f 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1013,9 +1013,13 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
 	 * If this zone is not populated, then it is not in zonelist.
 	 * This means the page allocator ignores this zone.
 	 * So, zonelist must be updated after online.
+	 *
+	 * If this zone is populated, zone->pageset could be initialized
+	 * to boot_pageset for the first time a node is added. If so,
+	 * zone->pageset should be allocated.
 	 */
 	mutex_lock(&zonelists_mutex);
-	if (!populated_zone(zone)) {
+	if (!populated_zone(zone) || !zone_pcp_initialized(zone)) {
 		need_zonelists_rebuild = 1;
 		build_all_zonelists(NULL, zone);
 	}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 736d8e1..4ff1540 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -6456,6 +6456,11 @@ void __meminit zone_pcp_update(struct zone *zone)
 }
 #endif
 
+bool zone_pcp_initialized(struct zone *zone)
+{
+	return (zone->pageset != &boot_pageset);
+}
+
 void zone_pcp_reset(struct zone *zone)
 {
 	unsigned long flags;
-- 
1.8.3.1

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