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

Yue Zhao
2023-02-20T15:17:30Z

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@gmail.com>
---
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