[PATCH] mm/memcontrol: stop resize loop if limit was changed again

[Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx>]

In memory_max_write() we first set memcg->memory.max and only then
try to enforce it in loop. What if while we are in loop someone else
have changed memcg->memory.max but we are still trying to enforce
the old value? I believe this can lead to nasty consequence like getting
an oom on perfectly fine cgroup within it's limits or excess reclaim.

We also have exactly the same thing in memory_high_write().

So let's stop enforcing old limits if we already have a new ones.

Signed-off-by: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx>
---
 mm/memcontrol.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 61932c9215e7..81b303728491 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -6769,6 +6769,9 @@ static ssize_t memory_high_write(struct kernfs_open_file *of,
 		unsigned long nr_pages = page_counter_read(&memcg->memory);
 		unsigned long reclaimed;
 
+		if (memcg->memory.high != high)
+			break;
+
 		if (nr_pages <= high)
 			break;
 
@@ -6817,6 +6820,9 @@ static ssize_t memory_max_write(struct kernfs_open_file *of,
 	for (;;) {
 		unsigned long nr_pages = page_counter_read(&memcg->memory);
 
+		if (memcg->memory.max != max)
+			break;
+
 		if (nr_pages <= max)
 			break;
 
-- 
2.43.0