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    SubjectRe: [PATCH 4/6] mm, memcg: Prevent memory.min load/store tearing
    On Thu 12-03-20 17:33:07, 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@chrisdown.name>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Johannes Weiner <hannes@cmpxchg.org>
    > Cc: Roman Gushchin <guro@fb.com>
    > Cc: Tejun Heo <tj@kernel.org>
    > Cc: linux-mm@kvack.org
    > Cc: cgroups@vger.kernel.org
    > Cc: linux-kernel@vger.kernel.org
    > Cc: kernel-team@fb.com

    Acked-by: Michal Hocko <mhocko@suse.com>

    > ---
    > mm/memcontrol.c | 4 ++--
    > mm/page_counter.c | 10 ++++++----
    > 2 files changed, 8 insertions(+), 6 deletions(-)
    >
    > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
    > index c85a304fa4a1..e0ed790a2a8c 100644
    > --- a/mm/memcontrol.c
    > +++ b/mm/memcontrol.c
    > @@ -6261,7 +6261,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
    > if (!usage)
    > return MEMCG_PROT_NONE;
    >
    > - emin = memcg->memory.min;
    > + emin = READ_ONCE(memcg->memory.min);
    > elow = READ_ONCE(memcg->memory.low);
    >
    > parent = parent_mem_cgroup(memcg);
    > @@ -6277,7 +6277,7 @@ enum mem_cgroup_protection mem_cgroup_protected(struct mem_cgroup *root,
    > if (emin && parent_emin) {
    > unsigned long min_usage, siblings_min_usage;
    >
    > - min_usage = min(usage, memcg->memory.min);
    > + min_usage = min(usage, READ_ONCE(memcg->memory.min));
    > siblings_min_usage = atomic_long_read(
    > &parent->memory.children_min_usage);
    >
    > diff --git a/mm/page_counter.c b/mm/page_counter.c
    > index 18b7f779f2e2..ae471c7d255f 100644
    > --- a/mm/page_counter.c
    > +++ b/mm/page_counter.c
    > @@ -17,14 +17,16 @@ static void propagate_protected_usage(struct page_counter *c,
    > 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)) {
    > - if (usage <= c->min)
    > + min = READ_ONCE(c->min);
    > +
    > + if (min || atomic_long_read(&c->min_usage)) {
    > + if (usage <= min)
    > protected = usage;
    > else
    > protected = 0;
    > @@ -217,7 +219,7 @@ void page_counter_set_min(struct page_counter *counter, unsigned long nr_pages)
    > {
    > 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));
    > --
    > 2.25.1
    >

    --
    Michal Hocko
    SUSE Labs

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