On Mon 06-03-23 23:41:37, Yue Zhao wrote:
> The knob for cgroup v1 memory controller: memory.oom_control
> is not protected by any locking so it can be modified while it is used.
> This is not an actual problem because races are unlikely.
> But it is better to use READ_ONCE/WRITE_ONCE to prevent compiler from
> doing anything funky.
>
> The access of memcg->oom_kill_disable is lockless,
> so it can be concurrently set at the same time as we are
> trying to read it.
>
> Signed-off-by: Yue Zhao <findns94@xxxxxxxxx>
> ---
> mm/memcontrol.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index dca895c66a9b..26605b2f51b1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4515,7 +4515,7 @@ static int mem_cgroup_oom_control_read(struct seq_file *sf, void *v)
> {
> struct mem_cgroup *memcg = mem_cgroup_from_seq(sf);
>
> - seq_printf(sf, "oom_kill_disable %d\n", memcg->oom_kill_disable);
> + seq_printf(sf, "oom_kill_disable %d\n", READ_ONCE(memcg->oom_kill_disable));
> seq_printf(sf, "under_oom %d\n", (bool)memcg->under_oom);
> seq_printf(sf, "oom_kill %lu\n",
> atomic_long_read(&memcg->memory_events[MEMCG_OOM_KILL]));
> @@ -4531,7 +4531,7 @@ static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
> if (mem_cgroup_is_root(memcg) || !((val == 0) || (val == 1)))
> return -EINVAL;
>
> - memcg->oom_kill_disable = val;
> + WRITE_ONCE(memcg->oom_kill_disable, val);
> if (!val)
> memcg_oom_recover(memcg);
Any specific reasons you haven't covered other accesses
(mem_cgroup_css_alloc, mem_cgroup_oom, mem_cgroup_oom_synchronize)?
>
> --
> 2.17.1
--
Michal Hocko
SUSE Labs
