Commit 6360d444 authored Dec 03, 2025 by Guopeng Zhang Committed by Tejun Heo Dec 08, 2025

selftests: cgroup: make test_memcg_sock robust against delayed sock stats



test_memcg_sock() currently requires that memory.stat's "sock " counter
is exactly zero immediately after the TCP server exits. On a busy system
this assumption is too strict:

  - Socket memory may be freed with a small delay (e.g. RCU callbacks).
  - memcg statistics are updated asynchronously via the rstat flushing
    worker, so the "sock " value in memory.stat can stay non-zero for a
    short period of time even after all socket memory has been uncharged.

As a result, test_memcg_sock() can intermittently fail even though socket
memory accounting is working correctly.

Make the test more robust by polling memory.stat for the "sock "
counter and allowing it some time to drop to zero instead of checking
it only once. The timeout is set to 3 seconds to cover the periodic
rstat flush interval (FLUSH_TIME = 2*HZ by default) plus some
scheduling slack. If the counter does not become zero within the
timeout, the test still fails as before.

On my test system, running test_memcontrol 50 times produced:

  - Before this patch:  6/50 runs passed.
  - After this patch:  50/50 runs passed.

Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
Suggested-by: Lance Yang <lance.yang@linux.dev>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

parent 311ead1b

tools/testing/selftests/cgroup/test_memcontrol.c

+19 −1

Original line number	Diff line number	Diff line
		@@ -21,6 +21,8 @@
		#include "kselftest.h"
		#include "cgroup_util.h"

		#define MEMCG_SOCKSTAT_WAIT_RETRIES 30

		static bool has_localevents;
		static bool has_recursiveprot;

		@@ -1384,6 +1386,7 @@ static int test_memcg_sock(const char *root)
		int bind_retries = 5, ret = KSFT_FAIL, pid, err;
		unsigned short port;
		char *memcg;
		long sock_post = -1;

		memcg = cg_name(root, "memcg_test");
		if (!memcg)
		@@ -1432,7 +1435,22 @@ static int test_memcg_sock(const char *root)
		if (cg_read_long(memcg, "memory.current") < 0)
		goto cleanup;

		if (cg_read_key_long(memcg, "memory.stat", "sock "))
		/*
		* memory.stat is updated asynchronously via the memcg rstat
		* flushing worker, which runs periodically (every 2 seconds,
		* see FLUSH_TIME). On a busy system, the "sock " counter may
		* stay non-zero for a short period of time after the TCP
		* connection is closed and all socket memory has been
		* uncharged.
		*
		* Poll memory.stat for up to 3 seconds (~FLUSH_TIME plus some
		* scheduling slack) and require that the "sock " counter
		* eventually drops to zero.
		*/
		sock_post = cg_read_key_long_poll(memcg, "memory.stat", "sock ", 0,
		MEMCG_SOCKSTAT_WAIT_RETRIES,
		DEFAULT_WAIT_INTERVAL_US);
		if (sock_post)
		goto cleanup;

		ret = KSFT_PASS;