sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 407 insertions, 0 deletions

diff --git a/tools/perf/tests/dso-data.c b/tools/perf/tests/dso-data.c
new file mode 100644
index 000000000..46bc3f597
--- /dev/null
+++ b/tools/perf/tests/dso-data.c
@@ -0,0 +1,407 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <dirent.h>
+#include <stdlib.h>
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <api/fs/fs.h>
+#include "dso.h"
+#include "dsos.h"
+#include "machine.h"
+#include "symbol.h"
+#include "tests.h"
+#include "debug.h"
+
+static char *test_file(int size)
+{
+#define TEMPL "/tmp/perf-test-XXXXXX"
+	static char buf_templ[sizeof(TEMPL)];
+	char *templ = buf_templ;
+	int fd, i;
+	unsigned char *buf;
+
+	strcpy(buf_templ, TEMPL);
+#undef TEMPL
+
+	fd = mkstemp(templ);
+	if (fd < 0) {
+		perror("mkstemp failed");
+		return NULL;
+	}
+
+	buf = malloc(size);
+	if (!buf) {
+		close(fd);
+		return NULL;
+	}
+
+	for (i = 0; i < size; i++)
+		buf[i] = (unsigned char) ((int) i % 10);
+
+	if (size != write(fd, buf, size))
+		templ = NULL;
+
+	free(buf);
+	close(fd);
+	return templ;
+}
+
+#define TEST_FILE_SIZE (DSO__DATA_CACHE_SIZE * 20)
+
+struct test_data_offset {
+	off_t offset;
+	u8 data[10];
+	int size;
+};
+
+static struct test_data_offset offsets[] = {
+	/* Fill first cache page. */
+	{
+		.offset = 10,
+		.data   = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
+		.size   = 10,
+	},
+	/* Read first cache page. */
+	{
+		.offset = 10,
+		.data   = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
+		.size   = 10,
+	},
+	/* Fill cache boundary pages. */
+	{
+		.offset = DSO__DATA_CACHE_SIZE - DSO__DATA_CACHE_SIZE % 10,
+		.data   = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
+		.size   = 10,
+	},
+	/* Read cache boundary pages. */
+	{
+		.offset = DSO__DATA_CACHE_SIZE - DSO__DATA_CACHE_SIZE % 10,
+		.data   = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
+		.size   = 10,
+	},
+	/* Fill final cache page. */
+	{
+		.offset = TEST_FILE_SIZE - 10,
+		.data   = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
+		.size   = 10,
+	},
+	/* Read final cache page. */
+	{
+		.offset = TEST_FILE_SIZE - 10,
+		.data   = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 },
+		.size   = 10,
+	},
+	/* Read final cache page. */
+	{
+		.offset = TEST_FILE_SIZE - 3,
+		.data   = { 7, 8, 9, 0, 0, 0, 0, 0, 0, 0 },
+		.size   = 3,
+	},
+};
+
+/* move it from util/dso.c for compatibility */
+static int dso__data_fd(struct dso *dso, struct machine *machine)
+{
+	int fd = -1;
+
+	if (dso__data_get_fd(dso, machine, &fd))
+		dso__data_put_fd(dso);
+
+	return fd;
+}
+
+static void dsos__delete(struct dsos *dsos)
+{
+	for (unsigned int i = 0; i < dsos->cnt; i++) {
+		struct dso *dso = dsos->dsos[i];
+
+		dso__data_close(dso);
+		unlink(dso__name(dso));
+	}
+	dsos__exit(dsos);
+}
+
+static int test__dso_data(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct machine machine;
+	struct dso *dso;
+	char *file = test_file(TEST_FILE_SIZE);
+	size_t i;
+
+	TEST_ASSERT_VAL("No test file", file);
+
+	memset(&machine, 0, sizeof(machine));
+	dsos__init(&machine.dsos);
+
+	dso = dso__new(file);
+	TEST_ASSERT_VAL("Failed to add dso", !dsos__add(&machine.dsos, dso));
+	TEST_ASSERT_VAL("Failed to access to dso",
+			dso__data_fd(dso, &machine) >= 0);
+
+	/* Basic 10 bytes tests. */
+	for (i = 0; i < ARRAY_SIZE(offsets); i++) {
+		struct test_data_offset *data = &offsets[i];
+		ssize_t size;
+		u8 buf[10];
+
+		memset(buf, 0, 10);
+		size = dso__data_read_offset(dso, &machine, data->offset,
+				     buf, 10);
+
+		TEST_ASSERT_VAL("Wrong size", size == data->size);
+		TEST_ASSERT_VAL("Wrong data", !memcmp(buf, data->data, 10));
+	}
+
+	/* Read cross multiple cache pages. */
+	{
+		ssize_t size;
+		int c;
+		u8 *buf;
+
+		buf = malloc(TEST_FILE_SIZE);
+		TEST_ASSERT_VAL("ENOMEM\n", buf);
+
+		/* First iteration to fill caches, second one to read them. */
+		for (c = 0; c < 2; c++) {
+			memset(buf, 0, TEST_FILE_SIZE);
+			size = dso__data_read_offset(dso, &machine, 10,
+						     buf, TEST_FILE_SIZE);
+
+			TEST_ASSERT_VAL("Wrong size",
+				size == (TEST_FILE_SIZE - 10));
+
+			for (i = 0; i < (size_t)size; i++)
+				TEST_ASSERT_VAL("Wrong data",
+					buf[i] == (i % 10));
+		}
+
+		free(buf);
+	}
+
+	dso__put(dso);
+	dsos__delete(&machine.dsos);
+	unlink(file);
+	return 0;
+}
+
+static long open_files_cnt(void)
+{
+	char path[PATH_MAX];
+	struct dirent *dent;
+	DIR *dir;
+	long nr = 0;
+
+	scnprintf(path, PATH_MAX, "%s/self/fd", procfs__mountpoint());
+	pr_debug("fd path: %s\n", path);
+
+	dir = opendir(path);
+	TEST_ASSERT_VAL("failed to open fd directory", dir);
+
+	while ((dent = readdir(dir)) != NULL) {
+		if (!strcmp(dent->d_name, ".") ||
+		    !strcmp(dent->d_name, ".."))
+			continue;
+
+		nr++;
+	}
+
+	closedir(dir);
+	return nr - 1;
+}
+
+static int dsos__create(int cnt, int size, struct dsos *dsos)
+{
+	int i;
+
+	dsos__init(dsos);
+
+	for (i = 0; i < cnt; i++) {
+		struct dso *dso;
+		char *file = test_file(size);
+
+		TEST_ASSERT_VAL("failed to get dso file", file);
+		dso = dso__new(file);
+		TEST_ASSERT_VAL("failed to get dso", dso);
+		TEST_ASSERT_VAL("failed to add dso", !dsos__add(dsos, dso));
+		dso__put(dso);
+	}
+
+	return 0;
+}
+
+static int set_fd_limit(int n)
+{
+	struct rlimit rlim;
+
+	if (getrlimit(RLIMIT_NOFILE, &rlim))
+		return -1;
+
+	pr_debug("file limit %ld, new %d\n", (long) rlim.rlim_cur, n);
+
+	rlim.rlim_cur = n;
+	return setrlimit(RLIMIT_NOFILE, &rlim);
+}
+
+static int test__dso_data_cache(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct machine machine;
+	long nr_end, nr = open_files_cnt();
+	int dso_cnt, limit, i, fd;
+
+	/* Rest the internal dso open counter limit. */
+	reset_fd_limit();
+
+	memset(&machine, 0, sizeof(machine));
+
+	/* set as system limit */
+	limit = nr * 4;
+	TEST_ASSERT_VAL("failed to set file limit", !set_fd_limit(limit));
+
+	/* and this is now our dso open FDs limit */
+	dso_cnt = limit / 2;
+	TEST_ASSERT_VAL("failed to create dsos\n",
+			!dsos__create(dso_cnt, TEST_FILE_SIZE, &machine.dsos));
+
+	for (i = 0; i < (dso_cnt - 1); i++) {
+		struct dso *dso = machine.dsos.dsos[i];
+
+		/*
+		 * Open dsos via dso__data_fd(), it opens the data
+		 * file and keep it open (unless open file limit).
+		 */
+		fd = dso__data_fd(dso, &machine);
+		TEST_ASSERT_VAL("failed to get fd", fd > 0);
+
+		if (i % 2) {
+			#define BUFSIZE 10
+			u8 buf[BUFSIZE];
+			ssize_t n;
+
+			n = dso__data_read_offset(dso, &machine, 0, buf, BUFSIZE);
+			TEST_ASSERT_VAL("failed to read dso", n == BUFSIZE);
+		}
+	}
+
+	/* verify the first one is already open */
+	TEST_ASSERT_VAL("dsos[0] is not open", dso__data(machine.dsos.dsos[0])->fd != -1);
+
+	/* open +1 dso to reach the allowed limit */
+	fd = dso__data_fd(machine.dsos.dsos[i], &machine);
+	TEST_ASSERT_VAL("failed to get fd", fd > 0);
+
+	/* should force the first one to be closed */
+	TEST_ASSERT_VAL("failed to close dsos[0]", dso__data(machine.dsos.dsos[0])->fd == -1);
+
+	/* cleanup everything */
+	dsos__delete(&machine.dsos);
+
+	/* Make sure we did not leak any file descriptor. */
+	nr_end = open_files_cnt();
+	pr_debug("nr start %ld, nr stop %ld\n", nr, nr_end);
+	TEST_ASSERT_VAL("failed leaking files", nr == nr_end);
+	return 0;
+}
+
+static long new_limit(int count)
+{
+	int fd = open("/dev/null", O_RDONLY);
+	long ret = fd;
+	if (count > 0)
+		ret = new_limit(--count);
+	close(fd);
+	return ret;
+}
+
+static int test__dso_data_reopen(struct test_suite *test __maybe_unused, int subtest __maybe_unused)
+{
+	struct machine machine;
+	long nr_end, nr = open_files_cnt(), lim = new_limit(3);
+	int fd, fd_extra;
+
+#define dso_0 (machine.dsos.dsos[0])
+#define dso_1 (machine.dsos.dsos[1])
+#define dso_2 (machine.dsos.dsos[2])
+
+	/* Rest the internal dso open counter limit. */
+	reset_fd_limit();
+
+	memset(&machine, 0, sizeof(machine));
+
+	/*
+	 * Test scenario:
+	 * - create 3 dso objects
+	 * - set process file descriptor limit to current
+	 *   files count + 3
+	 * - test that the first dso gets closed when we
+	 *   reach the files count limit
+	 */
+
+	/* Make sure we are able to open 3 fds anyway */
+	TEST_ASSERT_VAL("failed to set file limit",
+			!set_fd_limit((lim)));
+
+	TEST_ASSERT_VAL("failed to create dsos\n",
+			!dsos__create(3, TEST_FILE_SIZE, &machine.dsos));
+
+	/* open dso_0 */
+	fd = dso__data_fd(dso_0, &machine);
+	TEST_ASSERT_VAL("failed to get fd", fd > 0);
+
+	/* open dso_1 */
+	fd = dso__data_fd(dso_1, &machine);
+	TEST_ASSERT_VAL("failed to get fd", fd > 0);
+
+	/*
+	 * open extra file descriptor and we just
+	 * reached the files count limit
+	 */
+	fd_extra = open("/dev/null", O_RDONLY);
+	TEST_ASSERT_VAL("failed to open extra fd", fd_extra > 0);
+
+	/* open dso_2 */
+	fd = dso__data_fd(dso_2, &machine);
+	TEST_ASSERT_VAL("failed to get fd", fd > 0);
+
+	/*
+	 * dso_0 should get closed, because we reached
+	 * the file descriptor limit
+	 */
+	TEST_ASSERT_VAL("failed to close dso_0", dso__data(dso_0)->fd == -1);
+
+	/* open dso_0 */
+	fd = dso__data_fd(dso_0, &machine);
+	TEST_ASSERT_VAL("failed to get fd", fd > 0);
+
+	/*
+	 * dso_1 should get closed, because we reached
+	 * the file descriptor limit
+	 */
+	TEST_ASSERT_VAL("failed to close dso_1", dso__data(dso_1)->fd == -1);
+
+	/* cleanup everything */
+	close(fd_extra);
+	dsos__delete(&machine.dsos);
+
+	/* Make sure we did not leak any file descriptor. */
+	nr_end = open_files_cnt();
+	pr_debug("nr start %ld, nr stop %ld\n", nr, nr_end);
+	TEST_ASSERT_VAL("failed leaking files", nr == nr_end);
+	return 0;
+}
+
+
+static struct test_case tests__dso_data[] = {
+	TEST_CASE("read", dso_data),
+	TEST_CASE("cache", dso_data_cache),
+	TEST_CASE("reopen", dso_data_reopen),
+	{	.name = NULL, }
+};
+
+struct test_suite suite__dso_data = {
+	.desc = "DSO data tests",
+	.test_cases = tests__dso_data,
+};