On Mon 06-03-23 23:41:38, Yue Zhao wrote:
> The knob for cgroup v1 memory controller: memory.soft_limit_in_bytes
> 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->soft_limit is lockless,
> so it can be concurrently set at the same time as we are
> trying to read it.
Similar here. mem_cgroup_css_reset and mem_cgroup_css_alloc are not
covered.
>
> 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 26605b2f51b1..20566f59bbcb 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3728,7 +3728,7 @@ static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
> case RES_FAILCNT:
> return counter->failcnt;
> case RES_SOFT_LIMIT:
> - return (u64)memcg->soft_limit * PAGE_SIZE;
> + return (u64)READ_ONCE(memcg->soft_limit) * PAGE_SIZE;
> default:
> BUG();
> }
> @@ -3870,7 +3870,7 @@ static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
> if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
> ret = -EOPNOTSUPP;
> } else {
> - memcg->soft_limit = nr_pages;
> + WRITE_ONCE(memcg->soft_limit, nr_pages);
> ret = 0;
> }
> break;
> --
> 2.17.1
--
Michal Hocko
SUSE Labs
