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Subject[PATCH 4/6] mm, memcg: Prevent memory.min load/store tearing
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
---
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
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