From: Chris Down <chris@xxxxxxxxxxxxxx> Subject: mm, memcg: prevent mem_cgroup_protected store tearing The read side of this is all protected, but we can still tear if multiple iterations of mem_cgroup_protected are going at the same time. There's some intentional racing in mem_cgroup_protected which is ok, but load/store tearing should be avoided. Link: http://lkml.kernel.org/r/d1e9fbc0379fe8db475d82c8b6fbe048876e12ae.1584034301.git.chris@xxxxxxxxxxxxxx Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Roman Gushchin <guro@xxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/memcontrol.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/mm/memcontrol.c~mm-memcg-prevent-mem_cgroup_protected-store-tearing +++ a/mm/memcontrol.c @@ -6396,14 +6396,14 @@ enum mem_cgroup_protection mem_cgroup_pr parent_usage = page_counter_read(&parent->memory); - memcg->memory.emin = effective_protection(usage, parent_usage, + WRITE_ONCE(memcg->memory.emin, effective_protection(usage, parent_usage, READ_ONCE(memcg->memory.min), READ_ONCE(parent->memory.emin), - atomic_long_read(&parent->memory.children_min_usage)); + atomic_long_read(&parent->memory.children_min_usage))); - memcg->memory.elow = effective_protection(usage, parent_usage, + WRITE_ONCE(memcg->memory.elow, effective_protection(usage, parent_usage, memcg->memory.low, READ_ONCE(parent->memory.elow), - atomic_long_read(&parent->memory.children_low_usage)); + atomic_long_read(&parent->memory.children_low_usage))); out: if (usage <= memcg->memory.emin) _
