@@ -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
@@ -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);
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. Signed-off-by: Yue Zhao <findns94@gmail.com> --- include/linux/swap.h | 8 ++++---- mm/memcontrol.c | 6 +++--- 2 files changed, 7 insertions(+), 7 deletions(-)