From: Chris Down <chris@xxxxxxxxxxxxxx> Subject: mm, memcg: prevent memory.min load/store tearing This can be set concurrently with reads, which may cause the wrong value to be propagated. Link: http://lkml.kernel.org/r/e809b4e6b0c1626dac6945970de06409a180ee65.1584034301.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 | 5 +++-- mm/page_counter.c | 9 +++++---- 2 files changed, 8 insertions(+), 6 deletions(-) --- a/mm/memcontrol.c~mm-memcg-prevent-memorymin-load-store-tearing +++ a/mm/memcontrol.c @@ -6389,7 +6389,7 @@ enum mem_cgroup_protection mem_cgroup_pr return MEMCG_PROT_NONE; if (parent == root) { - memcg->memory.emin = memcg->memory.min; + memcg->memory.emin = READ_ONCE(memcg->memory.min); memcg->memory.elow = memcg->memory.low; goto out; } @@ -6397,7 +6397,8 @@ enum mem_cgroup_protection mem_cgroup_pr parent_usage = page_counter_read(&parent->memory); memcg->memory.emin = effective_protection(usage, parent_usage, - memcg->memory.min, READ_ONCE(parent->memory.emin), + READ_ONCE(memcg->memory.min), + READ_ONCE(parent->memory.emin), atomic_long_read(&parent->memory.children_min_usage)); memcg->memory.elow = effective_protection(usage, parent_usage, --- a/mm/page_counter.c~mm-memcg-prevent-memorymin-load-store-tearing +++ a/mm/page_counter.c @@ -17,14 +17,15 @@ static void propagate_protected_usage(st unsigned long usage) { unsigned long protected, old_protected; - unsigned long low; + unsigned long low, min; long delta; if (!c->parent) return; - if (c->min || atomic_long_read(&c->min_usage)) { - protected = min(usage, c->min); + min = READ_ONCE(c->min); + if (min || atomic_long_read(&c->min_usage)) { + protected = min(usage, min); old_protected = atomic_long_xchg(&c->min_usage, protected); delta = protected - old_protected; if (delta) @@ -207,7 +208,7 @@ void page_counter_set_min(struct page_co { struct page_counter *c; - counter->min = nr_pages; + WRITE_ONCE(counter->min, nr_pages); for (c = counter; c; c = c->parent) propagate_protected_usage(c, atomic_long_read(&c->usage)); _
