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, 343 insertions, 0 deletions

diff --git a/tools/perf/tests/api-io.c b/tools/perf/tests/api-io.c
new file mode 100644
index 000000000..0ba3d5cce
--- /dev/null
+++ b/tools/perf/tests/api-io.c
@@ -0,0 +1,343 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "debug.h"
+#include "tests.h"
+#include <api/io.h>
+#include <linux/kernel.h>
+#include <linux/zalloc.h>
+
+#define TEMPL "/tmp/perf-test-XXXXXX"
+
+#define EXPECT_EQUAL(val, expected)                             \
+do {								\
+	if (val != expected) {					\
+		pr_debug("%s:%d: %d != %d\n",			\
+			__FILE__, __LINE__, val, expected);	\
+		ret = -1;					\
+	}							\
+} while (0)
+
+#define EXPECT_EQUAL64(val, expected)                           \
+do {								\
+	if (val != expected) {					\
+		pr_debug("%s:%d: %lld != %lld\n",		\
+			__FILE__, __LINE__, val, expected);	\
+		ret = -1;					\
+	}							\
+} while (0)
+
+static int make_test_file(char path[PATH_MAX], const char *contents)
+{
+	ssize_t contents_len = strlen(contents);
+	int fd;
+
+	strcpy(path, TEMPL);
+	fd = mkstemp(path);
+	if (fd < 0) {
+		pr_debug("mkstemp failed");
+		return -1;
+	}
+	if (write(fd, contents, contents_len) < contents_len) {
+		pr_debug("short write");
+		close(fd);
+		unlink(path);
+		return -1;
+	}
+	close(fd);
+	return 0;
+}
+
+static int setup_test(char path[PATH_MAX], const char *contents,
+		      size_t buf_size, struct io *io)
+{
+	if (make_test_file(path, contents))
+		return -1;
+
+	io->fd = open(path, O_RDONLY);
+	if (io->fd < 0) {
+		pr_debug("Failed to open '%s'\n", path);
+		unlink(path);
+		return -1;
+	}
+	io->buf = malloc(buf_size);
+	if (io->buf == NULL) {
+		pr_debug("Failed to allocate memory");
+		close(io->fd);
+		unlink(path);
+		return -1;
+	}
+	io__init(io, io->fd, io->buf, buf_size);
+	return 0;
+}
+
+static void cleanup_test(char path[PATH_MAX], struct io *io)
+{
+	zfree(&io->buf);
+	close(io->fd);
+	unlink(path);
+}
+
+static int do_test_get_char(const char *test_string, size_t buf_size)
+{
+	char path[PATH_MAX];
+	struct io io;
+	int ch, ret = 0;
+	size_t i;
+
+	if (setup_test(path, test_string, buf_size, &io))
+		return -1;
+
+	for (i = 0; i < strlen(test_string); i++) {
+		ch = io__get_char(&io);
+
+		EXPECT_EQUAL(ch, test_string[i]);
+		EXPECT_EQUAL(io.eof, false);
+	}
+	ch = io__get_char(&io);
+	EXPECT_EQUAL(ch, -1);
+	EXPECT_EQUAL(io.eof, true);
+
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test_get_char(void)
+{
+	int i, ret = 0;
+	size_t j;
+
+	static const char *const test_strings[] = {
+		"12345678abcdef90",
+		"a\nb\nc\nd\n",
+		"\a\b\t\v\f\r",
+	};
+	for (i = 0; i <= 10; i++) {
+		for (j = 0; j < ARRAY_SIZE(test_strings); j++) {
+			if (do_test_get_char(test_strings[j], 1 << i))
+				ret = -1;
+		}
+	}
+	return ret;
+}
+
+static int do_test_get_hex(const char *test_string,
+			__u64 val1, int ch1,
+			__u64 val2, int ch2,
+			__u64 val3, int ch3,
+			bool end_eof)
+{
+	char path[PATH_MAX];
+	struct io io;
+	int ch, ret = 0;
+	__u64 hex;
+
+	if (setup_test(path, test_string, 4, &io))
+		return -1;
+
+	ch = io__get_hex(&io, &hex);
+	EXPECT_EQUAL64(hex, val1);
+	EXPECT_EQUAL(ch, ch1);
+
+	ch = io__get_hex(&io, &hex);
+	EXPECT_EQUAL64(hex, val2);
+	EXPECT_EQUAL(ch, ch2);
+
+	ch = io__get_hex(&io, &hex);
+	EXPECT_EQUAL64(hex, val3);
+	EXPECT_EQUAL(ch, ch3);
+
+	EXPECT_EQUAL(io.eof, end_eof);
+
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test_get_hex(void)
+{
+	int ret = 0;
+
+	if (do_test_get_hex("12345678abcdef90",
+				0x12345678abcdef90, -1,
+				0, -1,
+				0, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_hex("1\n2\n3\n",
+				1, '\n',
+				2, '\n',
+				3, '\n',
+				false))
+		ret = -1;
+
+	if (do_test_get_hex("12345678ABCDEF90;a;b",
+				0x12345678abcdef90, ';',
+				0xa, ';',
+				0xb, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_hex("0x1x2x",
+				0, 'x',
+				1, 'x',
+				2, 'x',
+				false))
+		ret = -1;
+
+	if (do_test_get_hex("x1x",
+				0, -2,
+				1, 'x',
+				0, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_hex("10000000000000000000000000000abcdefgh99i",
+				0xabcdef, 'g',
+				0, -2,
+				0x99, 'i',
+				false))
+		ret = -1;
+
+	return ret;
+}
+
+static int do_test_get_dec(const char *test_string,
+			__u64 val1, int ch1,
+			__u64 val2, int ch2,
+			__u64 val3, int ch3,
+			bool end_eof)
+{
+	char path[PATH_MAX];
+	struct io io;
+	int ch, ret = 0;
+	__u64 dec;
+
+	if (setup_test(path, test_string, 4, &io))
+		return -1;
+
+	ch = io__get_dec(&io, &dec);
+	EXPECT_EQUAL64(dec, val1);
+	EXPECT_EQUAL(ch, ch1);
+
+	ch = io__get_dec(&io, &dec);
+	EXPECT_EQUAL64(dec, val2);
+	EXPECT_EQUAL(ch, ch2);
+
+	ch = io__get_dec(&io, &dec);
+	EXPECT_EQUAL64(dec, val3);
+	EXPECT_EQUAL(ch, ch3);
+
+	EXPECT_EQUAL(io.eof, end_eof);
+
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test_get_dec(void)
+{
+	int ret = 0;
+
+	if (do_test_get_dec("12345678abcdef90",
+				12345678, 'a',
+				0, -2,
+				0, -2,
+				false))
+		ret = -1;
+
+	if (do_test_get_dec("1\n2\n3\n",
+				1, '\n',
+				2, '\n',
+				3, '\n',
+				false))
+		ret = -1;
+
+	if (do_test_get_dec("12345678;1;2",
+				12345678, ';',
+				1, ';',
+				2, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_dec("0x1x2x",
+				0, 'x',
+				1, 'x',
+				2, 'x',
+				false))
+		ret = -1;
+
+	if (do_test_get_dec("x1x",
+				0, -2,
+				1, 'x',
+				0, -1,
+				true))
+		ret = -1;
+
+	if (do_test_get_dec("10000000000000000000000000000000000000000000000000000000000123456789ab99c",
+				123456789, 'a',
+				0, -2,
+				99, 'c',
+				false))
+		ret = -1;
+
+	return ret;
+}
+
+static int test_get_line(void)
+{
+	char path[PATH_MAX];
+	struct io io;
+	char test_string[1024];
+	char *line = NULL;
+	size_t i, line_len = 0;
+	size_t buf_size = 128;
+	int ret = 0;
+
+	for (i = 0; i < 512; i++)
+		test_string[i] = 'a';
+	test_string[512] = '\n';
+	for (i = 513; i < 1023; i++)
+		test_string[i] = 'b';
+	test_string[1023] = '\0';
+
+	if (setup_test(path, test_string, buf_size, &io))
+		return -1;
+
+	EXPECT_EQUAL((int)io__getline(&io, &line, &line_len), 513);
+	EXPECT_EQUAL((int)strlen(line), 513);
+	for (i = 0; i < 512; i++)
+		EXPECT_EQUAL(line[i], 'a');
+	EXPECT_EQUAL(line[512], '\n');
+	EXPECT_EQUAL((int)io__getline(&io, &line, &line_len), 510);
+	for (i = 0; i < 510; i++)
+		EXPECT_EQUAL(line[i], 'b');
+
+	free(line);
+	cleanup_test(path, &io);
+	return ret;
+}
+
+static int test__api_io(struct test_suite *test __maybe_unused,
+			int subtest __maybe_unused)
+{
+	int ret = 0;
+
+	if (test_get_char())
+		ret = TEST_FAIL;
+	if (test_get_hex())
+		ret = TEST_FAIL;
+	if (test_get_dec())
+		ret = TEST_FAIL;
+	if (test_get_line())
+		ret = TEST_FAIL;
+	return ret;
+}
+
+DEFINE_SUITE("Test api io", api_io);