[PATCH] mm: change memcg->oom_group access with atomic operations

[Yue Zhao <findns94-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

The knob for cgroup v2 memory controller: memory.oom.group
will be read and written simultaneously by user space
programs, thus we'd better change memcg->oom_group access
with atomic operations to avoid concurrency problems.

Signed-off-by: Yue Zhao <findns94-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
---
 mm/memcontrol.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 73afff8062f9..e4695fb80bda 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2057,7 +2057,7 @@ struct mem_cgroup *mem_cgroup_get_oom_group(struct task_struct *victim,
 	 * highest-level memory cgroup with oom.group set.
 	 */
 	for (; memcg; memcg = parent_mem_cgroup(memcg)) {
-		if (memcg->oom_group)
+		if (READ_ONCE(memcg->oom_group))
 			oom_group = memcg;
 
 		if (memcg == oom_domain)
@@ -6569,7 +6569,7 @@ static int memory_oom_group_show(struct seq_file *m, void *v)
 {
 	struct mem_cgroup *memcg = mem_cgroup_from_seq(m);
 
-	seq_printf(m, "%d\n", memcg->oom_group);
+	seq_printf(m, "%d\n", READ_ONCE(memcg->oom_group));
 
 	return 0;
 }
@@ -6591,7 +6591,7 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
 	if (oom_group != 0 && oom_group != 1)
 		return -EINVAL;
 
-	memcg->oom_group = oom_group;
+	WRITE_ONCE(memcg->oom_group, oom_group);
 
 	return nbytes;
 }
-- 
2.17.1