On Thu 12-03-20 17:33:01, Chris Down wrote:
> This can be set concurrently with reads, which may cause the wrong value
> to be propagated.
>
> Signed-off-by: Chris Down <chris@xxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Roman Gushchin <guro@xxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: cgroups@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Cc: kernel-team@xxxxxx
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
> ---
> mm/memcontrol.c | 4 ++--
> mm/page_counter.c | 9 ++++++---
> 2 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index aca2964ea494..c85a304fa4a1 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6262,7 +6262,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
> return MEMCG_PROT_NONE;
>
> emin = memcg->memory.min;
> - elow = memcg->memory.low;
> + elow = READ_ONCE(memcg->memory.low);
>
> parent = parent_mem_cgroup(memcg);
> /* No parent means a non-hierarchical mode on v1 memcg */
> @@ -6291,7 +6291,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
> if (elow && parent_elow) {
> unsigned long low_usage, siblings_low_usage;
>
> - low_usage = min(usage, memcg->memory.low);
> + low_usage = min(usage, READ_ONCE(memcg->memory.low));
> siblings_low_usage = atomic_long_read(
> &parent->memory.children_low_usage);
>
> diff --git a/mm/page_counter.c b/mm/page_counter.c
> index 50184929b61f..18b7f779f2e2 100644
> --- a/mm/page_counter.c
> +++ b/mm/page_counter.c
> @@ -17,6 +17,7 @@ static void propagate_protected_usage(struct page_counter *c,
> unsigned long usage)
> {
> unsigned long protected, old_protected;
> + unsigned long low;
> long delta;
>
> if (!c->parent)
> @@ -34,8 +35,10 @@ static void propagate_protected_usage(struct page_counter *c,
> atomic_long_add(delta, &c->parent->children_min_usage);
> }
>
> - if (c->low || atomic_long_read(&c->low_usage)) {
> - if (usage <= c->low)
> + low = READ_ONCE(c->low);
> +
> + if (low || atomic_long_read(&c->low_usage)) {
> + if (usage <= low)
> protected = usage;
> else
> protected = 0;
> @@ -231,7 +234,7 @@ void page_counter_set_low(struct page_counter *counter, unsigned long nr_pages)
> {
> struct page_counter *c;
>
> - counter->low = nr_pages;
> + WRITE_ONCE(counter->low, nr_pages);
>
> for (c = counter; c; c = c->parent)
> propagate_protected_usage(c, atomic_long_read(&c->usage));
> --
> 2.25.1
>
--
Michal Hocko
SUSE Labs
