[LTP] [PATCH v2] memcg/memcontrol04: Fix judgment for recursive_protection

[Jin Guojie]

V2:
* Change the expected events in F depending on memory_recursiveprot

In Patch v1[1], the role of recursive_protection in cgoup v2 was not considered.

By carefully reading the algorithm in the kernel function
effective_protection(). When memory_recursiveprot is enabled, a
subgroup with usage > 0 can get unclaimed greater than 0.

The purpose of doing this should be to achieve the essential purpose
of recursive_protection: the sum of all subgroups' unprotected values
is equal to parent's unprotected values.

Even though the documentation does not give an explicit description
for recursive_memoryprot, it looks like the kernel's processing
algorithm is reasonable.

Based on the idea of [2], Patch v2 is rewritten to determine whether
memory_recursiveprot is enabled.

On distributions with memory_recursiveprot enabled by default (from
Ubuntu 22.04 to 24.10), running this passes:

memcontrol04.c:208: TPASS: Expect: (C oom events=0) == 0
memcontrol04.c:211: TPASS: Expect: (C low events=966) > 0
memcontrol04.c:208: TPASS: Expect: (D oom events=0) == 0
memcontrol04.c:211: TPASS: Expect: (D low events=966) > 0
memcontrol04.c:208: TPASS: Expect: (E oom events=0) == 0
memcontrol04.c:214: TPASS: Expect: (E low events=0) == 0
memcontrol04.c:208: TPASS: Expect: (F oom events=0) == 0
memcontrol04.c:211: TPASS: Expect: (F low events=874) > 0

[1] https://lists.linux.it/pipermail/ltp/2024-November/040946.html
[2] https://lore.kernel.org/ltp/20220222144511.GA12037@blackbody.suse.cz/

Signed-off-by: Jin Guojie <guojie.jin@gmail.com>
Suggested-by: Richard Palethorpe <rpalethorpe@suse.com>
Suggested-by: Michal Koutný <mkoutny@suse.com>
---
 include/tst_cgroup.h                              |  2 ++
 lib/tst_cgroup.c                                  | 12 ++++++++++++
 testcases/kernel/controllers/memcg/memcontrol04.c |  2 +-
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/include/tst_cgroup.h b/include/tst_cgroup.h
index d23a8e652..068ff8306 100644
--- a/include/tst_cgroup.h
+++ b/include/tst_cgroup.h
@@ -256,4 +256,6 @@ int safe_cg_occursin(const char *file, const int lineno,
                         const char *const file_name,
                         const char *const needle);

+int tst_cg_memory_recursiveprot(struct tst_cg_group *cg);
+
 #endif /* TST_CGROUP_H */
diff --git a/lib/tst_cgroup.c b/lib/tst_cgroup.c
index 6055015eb..9e3b21ed0 100644
--- a/lib/tst_cgroup.c
+++ b/lib/tst_cgroup.c
@@ -76,6 +76,8 @@ struct cgroup_root {
        int we_mounted_it:1;
        /* cpuset is in compatability mode */
        int no_cpuset_prefix:1;
+
+       int memory_recursiveprot:1;
 };

 /* Controller sub-systems */
@@ -592,6 +594,7 @@ static void cgroup_root_scan(const char *const mnt_type,
        }
        for (tok = strtok(mnt_opts, ","); tok; tok = strtok(NULL, ",")) {
                nsdelegate |= !strcmp("nsdelegate", tok);
+               root->memory_recursiveprot |=
!strcmp("memory_recursiveprot", tok);
        }

        if (root->ver && ctrl_field == root->ctrl_field)
@@ -718,6 +721,7 @@ mount:
                tst_res(TINFO, "Mounted V2 CGroups on %s", mnt_path);
                tst_cg_scan();
                roots[0].we_mounted_it = 1;
+               roots[0].memory_recursiveprot = 1;
                return;
        }

@@ -1509,3 +1513,11 @@ int safe_cg_occursin(const char *const file,
const int lineno,

        return !!strstr(buf, needle);
 }
+
+int tst_cg_memory_recursiveprot(struct tst_cg_group *cg)
+{
+       if (cg && cg->dirs_by_ctrl[0]->dir_root)
+               return cg->dirs_by_ctrl[0]->dir_root->memory_recursiveprot;
+       return 0;
+}
+
diff --git a/testcases/kernel/controllers/memcg/memcontrol04.c
b/testcases/kernel/controllers/memcg/memcontrol04.c
index 1b8d115f8..9e9d6ab6e 100644
--- a/testcases/kernel/controllers/memcg/memcontrol04.c
+++ b/testcases/kernel/controllers/memcg/memcontrol04.c
@@ -207,7 +207,7 @@ static void test_memcg_low(void)

                TST_EXP_EXPR(oom == 0, "(%c oom events=%ld) == 0", id, oom);

-               if (i < E) {
+               if (i < E || ((i == F) &&
tst_cg_memory_recursiveprot(leaf_cg[F]))) {
                        TST_EXP_EXPR(low > 0,
                                     "(%c low events=%ld) > 0", id, low);
                } else {
--
2.34.1