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From:   Wei Yang <richardw.yang@linux.intel.com>
To:     akpm@linux-foundation.org, osalvador@suse.de, mhocko@suse.com
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Wei Yang <richardw.yang@linux.intel.com>
Subject: [PATCH] mm/hotplug: prevent memory leak when reuse pgdat
Date:   Tue, 13 Aug 2019 10:06:08 +0800
Message-Id: <20190813020608.10194-1-richardw.yang@linux.intel.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

When offline a node in try_offline_node, pgdat is not released. So that
pgdat could be reused in hotadd_new_pgdat. While we re-allocate
pgdat->per_cpu_nodestats if this pgdat is reused.

This patch prevents the memory leak by just allocate per_cpu_nodestats
when it is a new pgdat.

NOTE: This is not tested since I didn't manage to create a case to
offline a whole node. If my analysis is not correct, please let me know.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
---
 mm/memory_hotplug.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index c73f09913165..efaf9e6f580a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -933,8 +933,11 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 		if (!pgdat)
 			return NULL;
 
+		pgdat->per_cpu_nodestats =
+			alloc_percpu(struct per_cpu_nodestat);
 		arch_refresh_nodedata(nid, pgdat);
 	} else {
+		int cpu;
 		/*
 		 * Reset the nr_zones, order and classzone_idx before reuse.
 		 * Note that kswapd will init kswapd_classzone_idx properly
@@ -943,6 +946,12 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 		pgdat->nr_zones = 0;
 		pgdat->kswapd_order = 0;
 		pgdat->kswapd_classzone_idx = 0;
+		for_each_online_cpu(cpu) {
+			struct per_cpu_nodestat *p;
+
+			p = per_cpu_ptr(pgdat->per_cpu_nodestats, cpu);
+			memset(p, 0, sizeof(*p));
+		}
 	}
 
 	/* we can use NODE_DATA(nid) from here */
@@ -952,7 +961,6 @@ static pg_data_t __ref *hotadd_new_pgdat(int nid, u64 start)
 
 	/* init node's zones as empty zones, we don't have any present pages.*/
 	free_area_init_core_hotplug(nid);
-	pgdat->per_cpu_nodestats = alloc_percpu(struct per_cpu_nodestat);
 
 	/*
 	 * The node we allocated has no zone fallback lists. For avoiding
-- 
2.17.1