[PATCH] selftests: cgroup: test memcg OOM on a process whose leader has exited

[Zhan Xusheng <zhanxusheng1024@gmail.com>]

From: Zhan Xusheng <zhanxusheng@xiaomi.com>

Moving a process whose thread group leader has exited leaves the leader
behind, so its live threads sit in the destination memcg with nothing
listed in cgroup.procs.  Check that an OOM there still kills the process.

Without "mm: memcontrol: don't miss processes whose leader has exited in
OOM scans" no task is selected and the test fails after five seconds.

Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
---
 .../selftests/cgroup/test_memcontrol.c        | 123 ++++++++++++++++++
 1 file changed, 123 insertions(+)

diff --git a/tools/testing/selftests/cgroup/test_memcontrol.c b/tools/testing/selftests/cgroup/test_memcontrol.c
index bb673012dcf0..bddbe923fa42 100644
--- a/tools/testing/selftests/cgroup/test_memcontrol.c
+++ b/tools/testing/selftests/cgroup/test_memcontrol.c
@@ -4,6 +4,8 @@
 #include <linux/limits.h>
 #include <linux/oom.h>
 #include <fcntl.h>
+#include <sched.h>
+#include <signal.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -18,6 +20,7 @@
 #include <netdb.h>
 #include <errno.h>
 #include <sys/mman.h>
+#include <sys/syscall.h>
 #include <sys/sysinfo.h>
 
 #include "kselftest.h"
@@ -1417,6 +1420,125 @@ static bool memcg_sockets_disabled(void)
  * The TCP client interleaves reads from the socket with check whether
  * memory.current and memory.stat.sock are similar.
  */
+static int exited_leader_pipe[2];
+
+static int exited_leader_thread(void *arg)
+{
+	char c;
+
+	/* Wait until the process has been moved, then fill memory. */
+	if (read(exited_leader_pipe[0], &c, 1) == 1)
+		alloc_anon(NULL, (void *)MB(100));
+	for (;;)
+		pause();
+	return 0;
+}
+
+/* Start a thread and exit only the thread group leader. */
+static int exited_leader_fn(const char *cgroup, void *arg)
+{
+	const size_t stack_size = 64 * 1024;
+	char *stack = malloc(stack_size);
+
+	if (!stack)
+		return EXIT_FAILURE;
+
+	if (clone(exited_leader_thread, stack + stack_size,
+		  CLONE_VM | CLONE_FS | CLONE_FILES | CLONE_SIGHAND |
+		  CLONE_THREAD | CLONE_SYSVSEM, NULL) < 0)
+		return EXIT_FAILURE;
+
+	syscall(SYS_exit, 0);
+	return EXIT_FAILURE;
+}
+
+/*
+ * Moving a process whose leader has exited leaves the leader behind, so
+ * the destination's cgroup.procs is empty.  Check that the destination's
+ * OOM killer still finds the process using its memory.
+ */
+static int test_memcg_oom_exited_leader(const char *root)
+{
+	char *parent = NULL, *src = NULL, *dst = NULL;
+	int ret = KSFT_FAIL;
+	pid_t pid = -ESRCH;
+	int i;
+
+	if (pipe(exited_leader_pipe))
+		return KSFT_FAIL;
+
+	parent = cg_name(root, "memcg_test_exited_leader");
+	if (!parent)
+		goto cleanup;
+	src = cg_name(parent, "src");
+	if (!src)
+		goto cleanup;
+	dst = cg_name(parent, "dst");
+	if (!dst)
+		goto cleanup;
+
+	if (cg_create(parent))
+		goto cleanup;
+	if (cg_write(parent, "cgroup.subtree_control", "+memory"))
+		goto cleanup;
+	if (cg_create(src) || cg_create(dst))
+		goto cleanup;
+	if (cg_write(dst, "memory.max", "30M"))
+		goto cleanup;
+	if (cg_write(dst, "memory.swap.max", "0"))
+		goto cleanup;
+
+	pid = cg_run_nowait(src, exited_leader_fn, NULL);
+	if (pid < 0)
+		goto cleanup;
+
+	for (i = 0; i < 100; i++) {
+		if (!proc_read_strstr(pid, false, "stat", ") Z "))
+			break;
+		usleep(10000);
+	}
+	if (i == 100)
+		goto cleanup;
+
+	/* The exited leader stays in src, the live thread moves. */
+	if (cg_enter(dst, pid))
+		goto cleanup;
+	if (cg_read_strcmp(dst, "cgroup.procs", ""))
+		goto cleanup;
+
+	if (write(exited_leader_pipe[1], "x", 1) != 1)
+		goto cleanup;
+
+	if (cg_read_key_long_poll(dst, "memory.events", "oom_kill ", 1,
+				  50, 100000) != 1)
+		goto cleanup;
+
+	if (cg_read_strcmp_wait(dst, "cgroup.events", "populated 0\n"))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	if (dst)
+		cg_write(dst, "cgroup.kill", "1");
+	if (pid > 0) {
+		kill(pid, SIGKILL);
+		waitpid(pid, NULL, 0);
+	}
+	close(exited_leader_pipe[0]);
+	close(exited_leader_pipe[1]);
+	if (dst)
+		cg_destroy(dst);
+	if (src)
+		cg_destroy(src);
+	if (parent)
+		cg_destroy(parent);
+	free(dst);
+	free(src);
+	free(parent);
+	return ret;
+}
+
 static int test_memcg_sock(const char *root)
 {
 	int bind_retries = 5, ret = KSFT_FAIL, pid, err;
@@ -1816,6 +1938,7 @@ struct memcg_test {
 	T(test_memcg_oom_group_leaf_events),
 	T(test_memcg_oom_group_parent_events),
 	T(test_memcg_oom_group_score_events),
+	T(test_memcg_oom_exited_leader),
 	T(test_memcg_inotify_delete_file),
 	T(test_memcg_inotify_delete_dir),
 };

base-commit: d135ab453a7400a34930bdda1ef4bdc8acfac80e
-- 
2.43.0