[PATCH v3 23/24] selftests/sched: Test SCHED_DEADLINE bandwidth across a root domain rebuild

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

Add deadline_rebuild_test, for the previous patch. In each case a task
of 400ms every second runs 380ms, then leaves SCHED_DEADLINE, its 0-lag
time some 570ms ahead; past that time, the one-CPU partition root P must
admit one task of 600ms every second and refuse a second with EBUSY:

 - dies_before_rebuild: the task, in P, exits, and a second partition
   root is made meanwhile, which rebuilds the accounting of every root
   domain;
 - switched_out_before_rebuild: the same, the task switched to
   SCHED_OTHER and asleep in P;
 - moved_after_switch_out: the task, outside P, switches to SCHED_OTHER,
   moves into P and dies there.

A kernel that removes the bandwidth from P's root domain when a rebuild
dropped it, or when P never had it, admits both. Skipped without root,
the cgroup v2 cpuset controller, deadline admission control (that is,
with sched_rt_runtime_us at -1) or 3 CPUs.

In 8 VMs of 8 vCPUs each, three runs in each, v7.4-rc1 fails the three
cases, and so does it with the patches of this series up to
"sched/deadline: Keep departing bandwidth across a root domain rebuild"
excluded; with it, the three pass; every time. v7.3 fails them as well
(2 VMs, three runs in each).

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---
 .../selftests/sched/deadline/.gitignore       |   1 +
 .../testing/selftests/sched/deadline/Makefile |   2 +-
 tools/testing/selftests/sched/deadline/config |   2 +
 .../sched/deadline/deadline_rebuild_test.c    | 462 ++++++++++++++++++
 4 files changed, 466 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/sched/deadline/config
 create mode 100644 tools/testing/selftests/sched/deadline/deadline_rebuild_test.c

diff --git a/tools/testing/selftests/sched/deadline/.gitignore b/tools/testing/selftests/sched/deadline/.gitignore
index 9f203c455b91..bf7dd0da81a9 100644
--- a/tools/testing/selftests/sched/deadline/.gitignore
+++ b/tools/testing/selftests/sched/deadline/.gitignore
@@ -1 +1,2 @@
 deadline_switch_test
+deadline_rebuild_test
diff --git a/tools/testing/selftests/sched/deadline/Makefile b/tools/testing/selftests/sched/deadline/Makefile
index 3f4dc1ec6119..f3a1d1746d22 100644
--- a/tools/testing/selftests/sched/deadline/Makefile
+++ b/tools/testing/selftests/sched/deadline/Makefile
@@ -3,6 +3,6 @@
 CFLAGS += -O2 -Wall -g -I./ $(KHDR_INCLUDES)
 LDLIBS += -lpthread
 
-TEST_GEN_PROGS := deadline_switch_test
+TEST_GEN_PROGS := deadline_switch_test deadline_rebuild_test
 
 include ../../lib.mk
diff --git a/tools/testing/selftests/sched/deadline/config b/tools/testing/selftests/sched/deadline/config
new file mode 100644
index 000000000000..d5bb793d742b
--- /dev/null
+++ b/tools/testing/selftests/sched/deadline/config
@@ -0,0 +1,2 @@
+CONFIG_CGROUPS=y
+CONFIG_CPUSETS=y
diff --git a/tools/testing/selftests/sched/deadline/deadline_rebuild_test.c b/tools/testing/selftests/sched/deadline/deadline_rebuild_test.c
new file mode 100644
index 000000000000..ccf462f27dd0
--- /dev/null
+++ b/tools/testing/selftests/sched/deadline/deadline_rebuild_test.c
@@ -0,0 +1,462 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * The bandwidth of a SCHED_DEADLINE task that leaves the policy, or dies,
+ * before its 0-lag time stays allocated in its root domain until the
+ * inactive timer removes it. It must be removed once, from the root
+ * domain that keeps it:
+ *
+ *  - dies: a task of a one-CPU partition root P dies, and a second
+ *    partition root Q is made meanwhile, which rebuilds the accounting
+ *    of every root domain;
+ *  - switched out: the same, the task switched to SCHED_OTHER;
+ *  - moved: a task outside P switched to SCHED_OTHER, then moved into P
+ *    before its 0-lag time.
+ *
+ * Then P, past the timer, must admit one task of 600ms every second and
+ * refuse a second one (EBUSY). A kernel that removes the bandwidth from
+ * P's root domain when the rebuild dropped it, or when P never held it,
+ * leaves it negative: it admits both.
+ *
+ * Needs root, the cgroup v2 cpuset controller, deadline admission
+ * control and 3 CPUs.
+ */
+#define _GNU_SOURCE
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <sched.h>
+#include <signal.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <sys/syscall.h>
+#include <sys/sysinfo.h>
+#include <sys/wait.h>
+#include <time.h>
+#include <unistd.h>
+
+#include "../../kselftest.h"
+
+#ifndef SCHED_DEADLINE
+#define SCHED_DEADLINE	6
+#endif
+
+#define NSEC_PER_MSEC	1000000ULL
+#define NSEC_PER_SEC	1000000000ULL
+
+struct dl_attr {
+	uint32_t size;
+	uint32_t sched_policy;
+	uint64_t sched_flags;
+	int32_t sched_nice;
+	uint32_t sched_priority;
+	uint64_t sched_runtime;
+	uint64_t sched_deadline;
+	uint64_t sched_period;
+};
+
+static char root[PATH_MAX], cg_p[PATH_MAX], cg_q[PATH_MAX];
+static int ncpus;
+
+static int set_deadline(pid_t pid, uint64_t runtime)
+{
+	struct dl_attr attr = {
+		.size = sizeof(attr),
+		.sched_policy = SCHED_DEADLINE,
+		.sched_runtime = runtime,
+		.sched_deadline = NSEC_PER_SEC,
+		.sched_period = NSEC_PER_SEC,
+	};
+
+	return syscall(__NR_sched_setattr, pid, &attr, 0) ? -errno : 0;
+}
+
+static int set_other(pid_t pid)
+{
+	struct sched_param sp = { .sched_priority = 0 };
+
+	return sched_setscheduler(pid, SCHED_OTHER, &sp) ? -errno : 0;
+}
+
+/* These clocks cannot fail: both are always supported, the pointer is valid. */
+static uint64_t now_ns(void)
+{
+	struct timespec ts;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	return ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec;
+}
+
+static void sleep_ns(uint64_t ns)
+{
+	struct timespec ts = { .tv_sec = ns / NSEC_PER_SEC, .tv_nsec = ns % NSEC_PER_SEC };
+
+	while (nanosleep(&ts, &ts) && errno == EINTR)
+		;
+}
+
+static void reap(pid_t pid)
+{
+	int status;
+
+	if (pid <= 0)
+		return;
+	if (kill(pid, SIGKILL) && errno != ESRCH)
+		ksft_print_msg("kill %d: %s\n", pid, strerror(errno));
+	set_other(pid);			/* gone already: nothing to switch */
+	while (waitpid(pid, &status, 0) != pid) {
+		if (errno == EINTR)
+			continue;
+		ksft_print_msg("waitpid %d: %s\n", pid, strerror(errno));
+		break;
+	}
+}
+
+static int write_file(const char *dir, const char *name, const char *val)
+{
+	char path[PATH_MAX];
+	int fd, err = 0;
+	ssize_t n;
+
+	if (snprintf(path, sizeof(path), "%s/%s", dir, name) >= (int)sizeof(path))
+		return -ENAMETOOLONG;
+	fd = open(path, O_WRONLY);
+	if (fd < 0)
+		return -errno;
+	n = write(fd, val, strlen(val));
+	if (n < 0)
+		err = -errno;
+	else if (n != (ssize_t)strlen(val))
+		err = -EIO;
+	if (close(fd) && !err)
+		err = -errno;
+	return err;
+}
+
+static int read_file(const char *path, char *buf, size_t len)
+{
+	int fd = open(path, O_RDONLY);
+	ssize_t n;
+
+	if (fd < 0)
+		return -1;
+	do {
+		n = read(fd, buf, len - 1);
+	} while (n < 0 && errno == EINTR);
+	close(fd);
+	if (n < 0)
+		return -1;
+	buf[n] = 0;
+	return 0;
+}
+
+static int enter(const char *cg, pid_t pid)
+{
+	char buf[16];
+
+	snprintf(buf, sizeof(buf), "%d", pid);
+	return write_file(cg, "cgroup.procs", buf);
+}
+
+/* A partition root of the one CPU @cpu, or -1. */
+static int make_partition(const char *cg, int cpu)
+{
+	char path[PATH_MAX], buf[32];
+
+	if (mkdir(cg, 0755) && errno != EEXIST)
+		return -1;
+	snprintf(buf, sizeof(buf), "%d", cpu);
+	if (write_file(cg, "cpuset.cpus", buf) || write_file(cg, "cpuset.cpus.partition", "root"))
+		return -1;
+	snprintf(path, sizeof(path), "%s/cpuset.cpus.partition", cg);
+	if (read_file(path, buf, sizeof(buf)) || strcmp(buf, "root\n"))
+		return -1;
+	return 0;
+}
+
+static void remove_partition(const char *cg)
+{
+	int err = write_file(cg, "cpuset.cpus.partition", "member");
+	uint64_t end;
+
+	if (err && err != -ENOENT)
+		ksft_print_msg("%s back to a member: %s\n", cg, strerror(-err));
+	/* A cgroup whose last task just died takes a moment to empty. */
+	end = now_ns() + NSEC_PER_SEC;
+	while (rmdir(cg)) {
+		if (errno == ENOENT)
+			return;
+		if (errno != EBUSY || now_ns() > end) {
+			ksft_print_msg("rmdir %s: %s\n", cg, strerror(errno));
+			return;
+		}
+		sleep_ns(10 * NSEC_PER_MSEC);
+	}
+}
+
+/* Both clocks are always supported and the pointer is valid: no error. */
+static uint64_t cpu_time_ns(void)
+{
+	struct timespec ts;
+
+	clock_gettime(CLOCK_THREAD_CPUTIME_ID, &ts);
+	return ts.tv_sec * NSEC_PER_SEC + ts.tv_nsec;
+}
+
+enum depart { DIES, SWITCHED_OUT };
+
+/*
+ * In @cg if given, made SCHED_DEADLINE at 400ms every second, the child
+ * runs 380ms of it, then dies or switches to SCHED_OTHER and sleeps:
+ * its 0-lag time is then some 570ms ahead. The pipe @fd gets a byte once
+ * it is out of the policy; for one that dies, its exit status tells. The
+ * caller keeps the read end alone.
+ */
+static pid_t departing(const char *cg, enum depart how, int fd[2])
+{
+	pid_t pid = fork();
+
+	if (pid < 0)
+		ksft_print_msg("fork: %s\n", strerror(errno));
+	if (!pid) {
+		uint64_t t0;
+
+		close(fd[0]);
+		if (cg && enter(cg, getpid()))
+			_exit(2);
+		if (set_deadline(0, 400 * NSEC_PER_MSEC))
+			_exit(3);
+		t0 = cpu_time_ns();
+		while (cpu_time_ns() - t0 < 380 * NSEC_PER_MSEC)
+			;
+		if (how == DIES)
+			_exit(0);
+		if (set_other(0) || write(fd[1], "x", 1) != 1)
+			_exit(4);
+		for (;;)
+			pause();
+	}
+	close(fd[1]);
+	fd[1] = -1;
+	return pid;
+}
+
+/* Wait until the child is out of SCHED_DEADLINE, dead or switched out. */
+static int departed(pid_t *pid, enum depart how, int fd)
+{
+	int status;
+	char c;
+
+	if (*pid < 0)
+		return -1;
+	/* No byte: the child failed, and its exit status tells. */
+	if (how == SWITCHED_OUT) {
+		ssize_t n;
+
+		do {
+			n = read(fd, &c, 1);
+		} while (n < 0 && errno == EINTR);
+		if (n == 1)
+			return 0;
+	}
+	if (waitpid(*pid, &status, 0) != *pid)
+		return -1;
+	*pid = -1;
+	return WIFEXITED(status) ? WEXITSTATUS(status) : -1;
+}
+
+/*
+ * A child that enters @cg and sleeps there, or -1. It moves itself, so
+ * that it last ran on a CPU of @cg, and says so once it is there.
+ */
+static pid_t sleeper(const char *cg)
+{
+	int fd[2];
+	pid_t pid;
+	char c;
+
+	if (pipe(fd))
+		return -1;
+	pid = fork();
+	if (pid < 0)
+		ksft_print_msg("fork: %s\n", strerror(errno));
+	if (!pid) {
+		close(fd[0]);
+		if (enter(cg, getpid()) || write(fd[1], "x", 1) != 1)
+			_exit(1);
+		for (;;)
+			pause();
+	}
+	close(fd[1]);
+	if (pid > 0 && read(fd[0], &c, 1) != 1) {
+		reap(pid);
+		pid = -1;
+	}
+	close(fd[0]);
+	return pid;
+}
+
+/* P, past every timer, admits one task of 600ms every second, not two. */
+static int check_p(void)
+{
+	pid_t a = sleeper(cg_p), b = sleeper(cg_p);
+	int ret = KSFT_FAIL, e1, e2;
+
+	if (a < 0 || b < 0) {
+		ksft_print_msg("no task could enter P\n");
+		goto out;
+	}
+	e1 = set_deadline(a, 600 * NSEC_PER_MSEC);
+	e2 = set_deadline(b, 600 * NSEC_PER_MSEC);
+	if (e1)
+		ksft_print_msg("a first task refused in P: %s\n", strerror(-e1));
+	else if (!e2)
+		ksft_print_msg("1.2 CPUs of deadline tasks admitted in a partition of one CPU\n");
+	else if (e2 != -EBUSY)
+		ksft_print_msg("the second task refused with %s, not EBUSY\n", strerror(-e2));
+	else
+		ret = KSFT_PASS;
+out:
+	reap(a);
+	reap(b);
+	return ret;
+}
+
+/* A task of P leaves, and Q is made before its 0-lag time. */
+static int test_rebuild(enum depart how)
+{
+	int ret = KSFT_FAIL, fd[2], err;
+	pid_t pid = -1;
+
+	if (pipe(fd))
+		return KSFT_FAIL;
+	if (make_partition(cg_p, ncpus - 1)) {
+		ksft_print_msg("no partition root on CPU %d\n", ncpus - 1);
+		ret = KSFT_SKIP;
+		goto out;
+	}
+	pid = departing(cg_p, how, fd);
+	err = departed(&pid, how, fd[0]);
+	if (err) {
+		ksft_print_msg("the deadline task failed (%d)\n", err);
+		goto out;
+	}
+	if (make_partition(cg_q, ncpus - 2)) {
+		ksft_print_msg("no partition root on CPU %d\n", ncpus - 2);
+		ret = KSFT_SKIP;
+		goto out;
+	}
+	/* Past the 0-lag time; one switched out sleeps on in P. */
+	sleep_ns(1500 * NSEC_PER_MSEC);
+	ret = check_p();
+out:
+	reap(pid);
+	remove_partition(cg_q);
+	remove_partition(cg_p);
+	close(fd[0]);
+	if (fd[1] >= 0)
+		close(fd[1]);
+	return ret;
+}
+
+/* A task outside P switches out, then moves into P before its 0-lag time. */
+static int test_move(void)
+{
+	int ret = KSFT_FAIL, fd[2], err;
+	pid_t pid = -1;
+
+	if (pipe(fd))
+		return KSFT_FAIL;
+	if (make_partition(cg_p, ncpus - 1)) {
+		ksft_print_msg("no partition root on CPU %d\n", ncpus - 1);
+		ret = KSFT_SKIP;
+		goto out;
+	}
+	pid = departing(NULL, SWITCHED_OUT, fd);
+	err = departed(&pid, SWITCHED_OUT, fd[0]);
+	if (err) {
+		ksft_print_msg("the deadline task failed (%d)\n", err);
+		goto out;
+	}
+	if (enter(cg_p, pid)) {
+		ksft_print_msg("the task cannot move into P\n");
+		goto out;
+	}
+	/* It wakes up, and dies, on P's CPU, before its 0-lag time. */
+	reap(pid);
+	pid = -1;
+	sleep_ns(1500 * NSEC_PER_MSEC);
+	ret = check_p();
+out:
+	reap(pid);
+	remove_partition(cg_p);
+	close(fd[0]);
+	if (fd[1] >= 0)
+		close(fd[1]);
+	return ret;
+}
+
+static int find_cgroup2(void)
+{
+	char line[PATH_MAX + 64], dev[64], dir[PATH_MAX], type[64];
+	FILE *f = fopen("/proc/self/mounts", "r");
+	int found = 0;
+
+	while (f && !found && fgets(line, sizeof(line), f)) {
+		if (sscanf(line, "%63s %4095s %63s", dev, dir, type) == 3 &&
+		    !strcmp(type, "cgroup2")) {
+			snprintf(root, sizeof(root), "%s", dir);
+			found = 1;
+		}
+	}
+	if (f)
+		fclose(f);
+	return found ? 0 : -1;
+}
+
+static void report(const char *name, int ret)
+{
+	if (ret == KSFT_PASS)
+		ksft_test_result_pass("%s\n", name);
+	else if (ret == KSFT_SKIP)
+		ksft_test_result_skip("%s\n", name);
+	else
+		ksft_test_result_fail("%s\n", name);
+}
+
+int main(void)
+{
+	char buf[256], path[PATH_MAX + 32];
+	int added;
+
+	ksft_print_header();
+	if (geteuid())
+		ksft_exit_skip("needs root\n");
+	ncpus = get_nprocs();
+	if (ncpus < 3)
+		ksft_exit_skip("needs 3 CPUs\n");
+	if (read_file("/proc/sys/kernel/sched_rt_runtime_us", buf, sizeof(buf)) || atol(buf) < 0)
+		ksft_exit_skip("no deadline admission control\n");
+	if (find_cgroup2())
+		ksft_exit_skip("cgroup v2 is not mounted\n");
+	/* The cpuset controller for the root's children while the test runs. */
+	snprintf(path, sizeof(path), "%s/cgroup.subtree_control", root);
+	if (read_file(path, buf, sizeof(buf)))
+		ksft_exit_skip("no cgroup.subtree_control\n");
+	added = !strstr(buf, "cpuset");
+	if (added && write_file(root, "cgroup.subtree_control", "+cpuset"))
+		ksft_exit_skip("no cpuset controller\n");
+	if (snprintf(cg_p, sizeof(cg_p), "%s/deadline_rebuild_p", root) >= (int)sizeof(cg_p) ||
+	    snprintf(cg_q, sizeof(cg_q), "%s/deadline_rebuild_q", root) >= (int)sizeof(cg_q))
+		ksft_exit_skip("cgroup v2 mount path too long\n");
+
+	ksft_set_plan(3);
+	report("dies_before_rebuild", test_rebuild(DIES));
+	report("switched_out_before_rebuild", test_rebuild(SWITCHED_OUT));
+	report("moved_after_switch_out", test_move());
+	if (added && write_file(root, "cgroup.subtree_control", "-cpuset"))
+		ksft_print_msg("the cpuset controller stays enabled\n");
+	ksft_finished();
+}
-- 
2.47.3