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

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Date: Wed, 20 Mar 2024 18:03:30 +0800
From: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
To: Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Shakeel Butt <shakeel.butt@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: Vladimir Davydov <vdavydov.dev@...il.com>,
	cgroups@...r.kernel.org,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel@...nvz.org,
	Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
Subject: [PATCH] mm/memcontrol: stop resize loop if limit was changed again

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@...tuozzo.com>
---
 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