+ cgroup-removing-racy-check-in-test_memcg_sock.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: cgroup: removing racy check in test_memcg_sock()
has been added to the -mm tree.  Its filename is
     cgroup-removing-racy-check-in-test_memcg_sock.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/cgroup-removing-racy-check-in-test_memcg_sock.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/cgroup-removing-racy-check-in-test_memcg_sock.patch

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------------------------------------------------------
From: David Vernet <void@manifault.com>
Subject: cgroup: removing racy check in test_memcg_sock()

test_memcg_sock() in the cgroup memcg tests, verifies expected memory
accounting for sockets.  The test forks a process which functions as a TCP
server, and sends large buffers back and forth between itself (as the TCP
client) and the forked TCP server.  While doing so, it verifies that
memory.current and memory.stat.sock look correct.

There is currently a check in tcp_client() which asserts memory.current >=
memory.stat.sock.  This check is racy, as between memory.current and
memory.stat.sock being queried, a packet could come in which causes
mem_cgroup_charge_skmem() to be invoked.  This could cause
memory.stat.sock to exceed memory.current.  Reversing the order of
querying doesn't address the problem either, as memory may be reclaimed
between the two calls.  Instead, this patch just removes that assertion
altogether, and instead relies on the values_close() check that follows to
validate the expected accounting.

Link: https://lkml.kernel.org/r/20220422155728.3055914-5-void@manifault.com
Signed-off-by: David Vernet <void@manifault.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/cgroup/test_memcontrol.c |    3 ---
 1 file changed, 3 deletions(-)

--- a/tools/testing/selftests/cgroup/test_memcontrol.c~cgroup-removing-racy-check-in-test_memcg_sock
+++ a/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -993,9 +993,6 @@ static int tcp_client(const char *cgroup
 		if (current < 0 || sock < 0)
 			goto close_sk;
 
-		if (current < sock)
-			goto close_sk;
-
 		if (values_close(current, sock, 10)) {
 			ret = KSFT_PASS;
 			break;
_

Patches currently in -mm which might be from void@manifault.com are

cgroups-refactor-children-cgroups-in-memcg-tests.patch
cgroup-account-for-memory_recursiveprot-in-test_memcg_low.patch
cgroup-account-for-memory_localevents-in-test_memcg_oom_group_leaf_events.patch
cgroup-removing-racy-check-in-test_memcg_sock.patch
cgroup-fix-racy-check-in-alloc_pagecache_max_30m-helper-function.patch