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

[Chris Down]

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
---
 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