From: Yue Zhao Date: Mon, 6 Mar 2023 15:41:36 +0000 (+0800) Subject: mm, memcg: Prevent memory.swappiness load/store tearing X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=82b3aa2681ca92421c4b508e7c390000273c53fe;p=linux.git 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 --- diff --git a/include/linux/swap.h b/include/linux/swap.h index d5d0b54e90e8d..bfc3b06b5f8fa 100644 --- a/include/linux/swap.h +++ b/include/linux/swap.h @@ -620,18 +620,18 @@ static inline int mem_cgroup_swappiness(struct mem_cgroup *memcg) { /* Cgroup2 doesn't have per-cgroup swappiness */ if (cgroup_subsys_on_dfl(memory_cgrp_subsys)) - return vm_swappiness; + return READ_ONCE(vm_swappiness); /* root ? */ if (mem_cgroup_disabled() || mem_cgroup_is_root(memcg)) - return vm_swappiness; + return READ_ONCE(vm_swappiness); - return memcg->swappiness; + return READ_ONCE(memcg->swappiness); } #else static inline int mem_cgroup_swappiness(struct mem_cgroup *mem) { - return vm_swappiness; + return READ_ONCE(vm_swappiness); } #endif diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 06821e5f7604f..1b0112afcad3f 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);