selftests: cgroup: Add basic tests for pids controller

This commit adds (and wires in) new test program for checking basic pids
controller functionality -- restricting tasks in a cgroup and correct
event counting.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

tools/testing/selftests/cgroup/.gitignore

@@ -7,5 +7,6 @@ test_hugetlb_memcg
 test_kill
 test_kmem
 test_memcontrol
+test_pids
 test_zswap
 wait_inotify

tools/testing/selftests/cgroup/Makefile

@@ -15,6 +15,7 @@ TEST_GEN_PROGS += test_hugetlb_memcg
 TEST_GEN_PROGS += test_kill
 TEST_GEN_PROGS += test_kmem
 TEST_GEN_PROGS += test_memcontrol
+TEST_GEN_PROGS += test_pids
 TEST_GEN_PROGS += test_zswap
 
 LOCAL_HDRS += $(selfdir)/clone3/clone3_selftests.h $(selfdir)/pidfd/pidfd.h
@@ -29,4 +30,5 @@ $(OUTPUT)/test_hugetlb_memcg: cgroup_util.c
 $(OUTPUT)/test_kill: cgroup_util.c
 $(OUTPUT)/test_kmem: cgroup_util.c
 $(OUTPUT)/test_memcontrol: cgroup_util.c
+$(OUTPUT)/test_pids: cgroup_util.c
 $(OUTPUT)/test_zswap: cgroup_util.c

tools/testing/selftests/cgroup/test_pids.c

@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0
+#define _GNU_SOURCE
+
+#include <errno.h>
+#include <linux/limits.h>
+#include <signal.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "../kselftest.h"
+#include "cgroup_util.h"
+
+static int run_success(const char *cgroup, void *arg)
+{
+	return 0;
+}
+
+static int run_pause(const char *cgroup, void *arg)
+{
+	return pause();
+}
+
+/*
+ * This test checks that pids.max prevents forking new children above the
+ * specified limit in the cgroup.
+ */
+static int test_pids_max(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *cg_pids;
+	int pid;
+
+	cg_pids = cg_name(root, "pids_test");
+	if (!cg_pids)
+		goto cleanup;
+
+	if (cg_create(cg_pids))
+		goto cleanup;
+
+	if (cg_read_strcmp(cg_pids, "pids.max", "max\n"))
+		goto cleanup;
+
+	if (cg_write(cg_pids, "pids.max", "2"))
+		goto cleanup;
+
+	if (cg_enter_current(cg_pids))
+		goto cleanup;
+
+	pid = cg_run_nowait(cg_pids, run_pause, NULL);
+	if (pid < 0)
+		goto cleanup;
+
+	if (cg_run_nowait(cg_pids, run_success, NULL) != -1 || errno != EAGAIN)
+		goto cleanup;
+
+	if (kill(pid, SIGINT))
+		goto cleanup;
+
+	ret = KSFT_PASS;
+
+cleanup:
+	cg_enter_current(root);
+	cg_destroy(cg_pids);
+	free(cg_pids);
+
+	return ret;
+}
+
+/*
+ * This test checks that pids.events are counted in cgroup associated with pids.max
+ */
+static int test_pids_events(const char *root)
+{
+	int ret = KSFT_FAIL;
+	char *cg_parent = NULL, *cg_child = NULL;
+	int pid;
+
+	cg_parent = cg_name(root, "pids_parent");
+	cg_child = cg_name(cg_parent, "pids_child");
+	if (!cg_parent || !cg_child)
+		goto cleanup;
+
+	if (cg_create(cg_parent))
+		goto cleanup;
+	if (cg_write(cg_parent, "cgroup.subtree_control", "+pids"))
+		goto cleanup;
+	if (cg_create(cg_child))
+		goto cleanup;
+
+	if (cg_write(cg_parent, "pids.max", "2"))
+		goto cleanup;
+
+	if (cg_read_strcmp(cg_child, "pids.max", "max\n"))
+		goto cleanup;
+
+	if (cg_enter_current(cg_child))
+		goto cleanup;
+
+	pid = cg_run_nowait(cg_child, run_pause, NULL);
+	if (pid < 0)
+		goto cleanup;
+
+	if (cg_run_nowait(cg_child, run_success, NULL) != -1 || errno != EAGAIN)
+		goto cleanup;
+
+	if (kill(pid, SIGINT))
+		goto cleanup;
+
+	if (cg_read_key_long(cg_child, "pids.events", "max ") != 0)
+		goto cleanup;
+	if (cg_read_key_long(cg_parent, "pids.events", "max ") != 1)
+		goto cleanup;
+
+
+	ret = KSFT_PASS;
+
+cleanup:
+	cg_enter_current(root);
+	if (cg_child)
+		cg_destroy(cg_child);
+	if (cg_parent)
+		cg_destroy(cg_parent);
+	free(cg_child);
+	free(cg_parent);
+
+	return ret;
+}
+
+
+
+#define T(x) { x, #x }
+struct pids_test {
+	int (*fn)(const char *root);
+	const char *name;
+} tests[] = {
+	T(test_pids_max),
+	T(test_pids_events),
+};
+#undef T
+
+int main(int argc, char **argv)
+{
+	char root[PATH_MAX];
+
+	ksft_print_header();
+	ksft_set_plan(ARRAY_SIZE(tests));
+	if (cg_find_unified_root(root, sizeof(root), NULL))
+		ksft_exit_skip("cgroup v2 isn't mounted\n");
+
+	/*
+	 * Check that pids controller is available:
+	 * pids is listed in cgroup.controllers
+	 */
+	if (cg_read_strstr(root, "cgroup.controllers", "pids"))
+		ksft_exit_skip("pids controller isn't available\n");
+
+	if (cg_read_strstr(root, "cgroup.subtree_control", "pids"))
+		if (cg_write(root, "cgroup.subtree_control", "+pids"))
+			ksft_exit_skip("Failed to set pids controller\n");
+
+	for (int i = 0; i < ARRAY_SIZE(tests); i++) {
+		switch (tests[i].fn(root)) {
+		case KSFT_PASS:
+			ksft_test_result_pass("%s\n", tests[i].name);
+			break;
+		case KSFT_SKIP:
+			ksft_test_result_skip("%s\n", tests[i].name);
+			break;
+		default:
+			ksft_test_result_fail("%s\n", tests[i].name);
+			break;
+		}
+	}
+
+	ksft_finished();
+}