From: Yue Zhao Date: Mon, 6 Mar 2023 15:41:38 +0000 (+0800) Subject: mm, memcg: Prevent memory.soft_limit_in_bytes load/store tearing X-Git-Tag: v6.6.17~4989^2~324 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=2178e20c24406548c97b18a2d9781d16c35b8881;p=platform%2Fkernel%2Flinux-rpi.git mm, memcg: Prevent memory.soft_limit_in_bytes load/store tearing 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|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. All occurrences of memcg->soft_limit are updated with [READ|WRITE]_ONCE. [findns94@gmail.com: v3] Link: https://lkml.kernel.org/r/20230308162555.14195-5-findns94@gmail.com Link: https://lkml.kernel.org/r/20230306154138.3775-5-findns94@gmail.com Signed-off-by: Yue Zhao Acked-by: Shakeel Butt Acked-by: Roman Gushchin Acked-by: Michal Hocko Cc: Johannes Weiner Cc: Matthew Wilcox (Oracle) Cc: Muchun Song Cc: Tang Yizhou Signed-off-by: Andrew Morton --- diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5b7062d..13ec89c 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; @@ -5347,7 +5347,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) return ERR_CAST(memcg); page_counter_set_high(&memcg->memory, PAGE_COUNTER_MAX); - memcg->soft_limit = PAGE_COUNTER_MAX; + WRITE_ONCE(memcg->soft_limit, PAGE_COUNTER_MAX); #if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_ZSWAP) memcg->zswap_max = PAGE_COUNTER_MAX; #endif @@ -5502,7 +5502,7 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css) page_counter_set_min(&memcg->memory, 0); page_counter_set_low(&memcg->memory, 0); page_counter_set_high(&memcg->memory, PAGE_COUNTER_MAX); - memcg->soft_limit = PAGE_COUNTER_MAX; + WRITE_ONCE(memcg->soft_limit, PAGE_COUNTER_MAX); page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX); memcg_wb_domain_size_changed(memcg); }