mm: slince possible data races about pgdat->kswapd

maillist inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I6PKGM

Reference: https://lore.kernel.org/linux-mm/20220824071909.192535-1-wangkefeng.wang@huawei.com/

--------------------------------

The pgdat->kswapd could be accessed concurrently by kswapd_run() and
kcompactd(), it don't be protected by any lock, which could leads to
data races, adding READ/WRITE_ONCE() to slince it.
Signed-off-by: NKefeng Wang <wangkefeng.wang@huawei.com>

Conflicts:
	mm/compaction.c
	mm/vmscan.c
Signed-off-by: NZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

mm/compaction.c

@@ -1926,7 +1926,9 @@ static inline bool is_via_compact_memory(int order)
 
 static bool kswapd_is_running(pg_data_t *pgdat)
 {
-	return pgdat->kswapd && (pgdat->kswapd->state == TASK_RUNNING);
+	struct task_struct *t = READ_ONCE(pgdat->kswapd);
+
+	return t && (t->state == TASK_RUNNING);
 }
 
 /*

mm/vmscan.c

@@ -4331,7 +4331,7 @@ int kswapd_run(int nid)
 	int ret = 0;
 	struct task_struct *t;
 
-	if (pgdat->kswapd)
+	if (READ_ONCE(pgdat->kswapd))
 		return 0;
 
 	t = kthread_run(kswapd, pgdat, "kswapd%d", nid);
@@ -4341,7 +4341,7 @@ int kswapd_run(int nid)
 		pr_err("Failed to start kswapd on node %d\n", nid);
 		ret = PTR_ERR(t);
 	} else {
-		pgdat->kswapd = t;
+		WRITE_ONCE(pgdat->kswapd, t);
 	}
 	return ret;
 }
@@ -4352,11 +4352,11 @@ int kswapd_run(int nid)
  */
 void kswapd_stop(int nid)
 {
-	struct task_struct *kswapd = NODE_DATA(nid)->kswapd;
+	struct task_struct *kswapd = READ_ONCE(NODE_DATA(nid)->kswapd);
 
 	if (kswapd) {
 		kthread_stop(kswapd);
-		NODE_DATA(nid)->kswapd = NULL;
+		WRITE_ONCE(NODE_DATA(nid)->kswapd, NULL);
 	}
 }