From 82b3aa2681ca92421c4b508e7c390000273c53fe Mon Sep 17 00:00:00 2001 From: Yue Zhao Date: Mon, 6 Mar 2023 23:41:36 +0800 Subject: mm, memcg: Prevent memory.swappiness load/store tearing The knob for cgroup v1 memory controller: memory.swappiness 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->swappiness and vm_swappiness is lockless, so both of them can be concurrently set at the same time as we are trying to read them. All occurrences of memcg->swappiness and vm_swappiness are updated with [READ|WRITE]_ONCE. [findns94@gmail.com: v3] Link: https://lkml.kernel.org/r/20230308162555.14195-3-findns94@gmail.com Link: https://lkml.kernel.org/r/20230306154138.3775-3-findns94@gmail.com Signed-off-by: Yue Zhao Acked-by: Michal Hocko Acked-by: Shakeel Butt Acked-by: Roman Gushchin Cc: Johannes Weiner Cc: Matthew Wilcox (Oracle) Cc: Muchun Song Cc: Tang Yizhou Signed-off-by: Andrew Morton --- mm/memcontrol.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'mm/memcontrol.c') diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 06821e5f7604..1b0112afcad3 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4179,9 +4179,9 @@ static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css, return -EINVAL; if (!mem_cgroup_is_root(memcg)) - memcg->swappiness = val; + WRITE_ONCE(memcg->swappiness, val); else - vm_swappiness = val; + WRITE_ONCE(vm_swappiness, val); return 0; } @@ -5353,7 +5353,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) #endif page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX); if (parent) { - memcg->swappiness = mem_cgroup_swappiness(parent); + WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent)); memcg->oom_kill_disable = parent->oom_kill_disable; page_counter_init(&memcg->memory, &parent->memory); -- cgit v1.2.3