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, 330 insertions, 0 deletions

diff --git a/lib/math/test_div64.c b/lib/math/test_div64.c
new file mode 100644
index 000000000..3cd699b65
--- /dev/null
+++ b/lib/math/test_div64.c
@@ -0,0 +1,330 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2021  Maciej W. Rozycki
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/ktime.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+#include <linux/time64.h>
+#include <linux/types.h>
+
+#include <asm/div64.h>
+
+#define TEST_DIV64_N_ITER 1024
+
+static const u64 test_div64_dividends[] = {
+	0x00000000ab275080,
+	0x0000000fe73c1959,
+	0x000000e54c0a74b1,
+	0x00000d4398ff1ef9,
+	0x0000a18c2ee1c097,
+	0x00079fb80b072e4a,
+	0x0072db27380dd689,
+	0x0842f488162e2284,
+	0xf66745411d8ab063,
+	0xfffffffffffffffb,
+	0xfffffffffffffffc,
+	0xffffffffffffffff,
+};
+#define SIZE_DIV64_DIVIDENDS ARRAY_SIZE(test_div64_dividends)
+
+#define TEST_DIV64_DIVISOR_0 0x00000009
+#define TEST_DIV64_DIVISOR_1 0x0000007c
+#define TEST_DIV64_DIVISOR_2 0x00000204
+#define TEST_DIV64_DIVISOR_3 0x0000cb5b
+#define TEST_DIV64_DIVISOR_4 0x00010000
+#define TEST_DIV64_DIVISOR_5 0x0008a880
+#define TEST_DIV64_DIVISOR_6 0x003fd3ae
+#define TEST_DIV64_DIVISOR_7 0x0b658fac
+#define TEST_DIV64_DIVISOR_8 0x80000001
+#define TEST_DIV64_DIVISOR_9 0xdc08b349
+#define TEST_DIV64_DIVISOR_A 0xfffffffe
+#define TEST_DIV64_DIVISOR_B 0xffffffff
+
+static const u32 test_div64_divisors[] = {
+	TEST_DIV64_DIVISOR_0,
+	TEST_DIV64_DIVISOR_1,
+	TEST_DIV64_DIVISOR_2,
+	TEST_DIV64_DIVISOR_3,
+	TEST_DIV64_DIVISOR_4,
+	TEST_DIV64_DIVISOR_5,
+	TEST_DIV64_DIVISOR_6,
+	TEST_DIV64_DIVISOR_7,
+	TEST_DIV64_DIVISOR_8,
+	TEST_DIV64_DIVISOR_9,
+	TEST_DIV64_DIVISOR_A,
+	TEST_DIV64_DIVISOR_B,
+};
+#define SIZE_DIV64_DIVISORS ARRAY_SIZE(test_div64_divisors)
+
+static const struct {
+	u64 quotient;
+	u32 remainder;
+} test_div64_results[SIZE_DIV64_DIVIDENDS][SIZE_DIV64_DIVISORS] = {
+	{
+		{ 0x0000000013045e47, 0x00000001 },
+		{ 0x000000000161596c, 0x00000030 },
+		{ 0x000000000054e9d4, 0x00000130 },
+		{ 0x000000000000d776, 0x0000278e },
+		{ 0x000000000000ab27, 0x00005080 },
+		{ 0x00000000000013c4, 0x0004ce80 },
+		{ 0x00000000000002ae, 0x001e143c },
+		{ 0x000000000000000f, 0x0033e56c },
+		{ 0x0000000000000001, 0x2b27507f },
+		{ 0x0000000000000000, 0xab275080 },
+		{ 0x0000000000000000, 0xab275080 },
+		{ 0x0000000000000000, 0xab275080 },
+	}, {
+		{ 0x00000001c45c02d1, 0x00000000 },
+		{ 0x0000000020d5213c, 0x00000049 },
+		{ 0x0000000007e3d65f, 0x000001dd },
+		{ 0x0000000000140531, 0x000065ee },
+		{ 0x00000000000fe73c, 0x00001959 },
+		{ 0x000000000001d637, 0x0004e5d9 },
+		{ 0x0000000000003fc9, 0x000713bb },
+		{ 0x0000000000000165, 0x029abe7d },
+		{ 0x000000000000001f, 0x673c193a },
+		{ 0x0000000000000012, 0x6e9f7e37 },
+		{ 0x000000000000000f, 0xe73c1977 },
+		{ 0x000000000000000f, 0xe73c1968 },
+	}, {
+		{ 0x000000197a3a0cf7, 0x00000002 },
+		{ 0x00000001d9632e5c, 0x00000021 },
+		{ 0x0000000071c28039, 0x000001cd },
+		{ 0x000000000120a844, 0x0000b885 },
+		{ 0x0000000000e54c0a, 0x000074b1 },
+		{ 0x00000000001a7bb3, 0x00072331 },
+		{ 0x00000000000397ad, 0x0002c61b },
+		{ 0x000000000000141e, 0x06ea2e89 },
+		{ 0x00000000000001ca, 0x4c0a72e7 },
+		{ 0x000000000000010a, 0xab002ad7 },
+		{ 0x00000000000000e5, 0x4c0a767b },
+		{ 0x00000000000000e5, 0x4c0a7596 },
+	}, {
+		{ 0x0000017949e37538, 0x00000001 },
+		{ 0x0000001b62441f37, 0x00000055 },
+		{ 0x0000000694a3391d, 0x00000085 },
+		{ 0x0000000010b2a5d2, 0x0000a753 },
+		{ 0x000000000d4398ff, 0x00001ef9 },
+		{ 0x0000000001882ec6, 0x0005cbf9 },
+		{ 0x000000000035333b, 0x0017abdf },
+		{ 0x00000000000129f1, 0x0ab4520d },
+		{ 0x0000000000001a87, 0x18ff0472 },
+		{ 0x0000000000000f6e, 0x8ac0ce9b },
+		{ 0x0000000000000d43, 0x98ff397f },
+		{ 0x0000000000000d43, 0x98ff2c3c },
+	}, {
+		{ 0x000011f321a74e49, 0x00000006 },
+		{ 0x0000014d8481d211, 0x0000005b },
+		{ 0x0000005025cbd92d, 0x000001e3 },
+		{ 0x00000000cb5e71e3, 0x000043e6 },
+		{ 0x00000000a18c2ee1, 0x0000c097 },
+		{ 0x0000000012a88828, 0x00036c97 },
+		{ 0x000000000287f16f, 0x002c2a25 },
+		{ 0x00000000000e2cc7, 0x02d581e3 },
+		{ 0x0000000000014318, 0x2ee07d7f },
+		{ 0x000000000000bbf4, 0x1ba08c03 },
+		{ 0x000000000000a18c, 0x2ee303af },
+		{ 0x000000000000a18c, 0x2ee26223 },
+	}, {
+		{ 0x0000d8db8f72935d, 0x00000005 },
+		{ 0x00000fbd5aed7a2e, 0x00000002 },
+		{ 0x000003c84b6ea64a, 0x00000122 },
+		{ 0x0000000998fa8829, 0x000044b7 },
+		{ 0x000000079fb80b07, 0x00002e4a },
+		{ 0x00000000e16b20fa, 0x0002a14a },
+		{ 0x000000001e940d22, 0x00353b2e },
+		{ 0x0000000000ab40ac, 0x06fba6ba },
+		{ 0x00000000000f3f70, 0x0af7eeda },
+		{ 0x000000000008debd, 0x72d98365 },
+		{ 0x0000000000079fb8, 0x0b166dba },
+		{ 0x0000000000079fb8, 0x0b0ece02 },
+	}, {
+		{ 0x000cc3045b8fc281, 0x00000000 },
+		{ 0x0000ed1f48b5c9fc, 0x00000079 },
+		{ 0x000038fb9c63406a, 0x000000e1 },
+		{ 0x000000909705b825, 0x00000a62 },
+		{ 0x00000072db27380d, 0x0000d689 },
+		{ 0x0000000d43fce827, 0x00082b09 },
+		{ 0x00000001ccaba11a, 0x0037e8dd },
+		{ 0x000000000a13f729, 0x0566dffd },
+		{ 0x0000000000e5b64e, 0x3728203b },
+		{ 0x000000000085a14b, 0x23d36726 },
+		{ 0x000000000072db27, 0x38f38cd7 },
+		{ 0x000000000072db27, 0x3880b1b0 },
+	}, {
+		{ 0x00eafeb9c993592b, 0x00000001 },
+		{ 0x00110e5befa9a991, 0x00000048 },
+		{ 0x00041947b4a1d36a, 0x000000dc },
+		{ 0x00000a6679327311, 0x0000c079 },
+		{ 0x00000842f488162e, 0x00002284 },
+		{ 0x000000f4459740fc, 0x00084484 },
+		{ 0x0000002122c47bf9, 0x002ca446 },
+		{ 0x00000000b9936290, 0x004979c4 },
+		{ 0x000000001085e910, 0x05a83974 },
+		{ 0x00000000099ca89d, 0x9db446bf },
+		{ 0x000000000842f488, 0x26b40b94 },
+		{ 0x000000000842f488, 0x1e71170c },
+	}, {
+		{ 0x1b60cece589da1d2, 0x00000001 },
+		{ 0x01fcb42be1453f5b, 0x0000004f },
+		{ 0x007a3f2457df0749, 0x0000013f },
+		{ 0x0001363130e3ec7b, 0x000017aa },
+		{ 0x0000f66745411d8a, 0x0000b063 },
+		{ 0x00001c757dfab350, 0x00048863 },
+		{ 0x000003dc4979c652, 0x00224ea7 },
+		{ 0x000000159edc3144, 0x06409ab3 },
+		{ 0x00000001ecce8a7e, 0x30bc25e5 },
+		{ 0x000000011eadfee3, 0xa99c48a8 },
+		{ 0x00000000f6674543, 0x0a593ae9 },
+		{ 0x00000000f6674542, 0x13f1f5a5 },
+	}, {
+		{ 0x1c71c71c71c71c71, 0x00000002 },
+		{ 0x0210842108421084, 0x0000000b },
+		{ 0x007f01fc07f01fc0, 0x000000fb },
+		{ 0x00014245eabf1f9a, 0x0000a63d },
+		{ 0x0000ffffffffffff, 0x0000fffb },
+		{ 0x00001d913cecc509, 0x0007937b },
+		{ 0x00000402c70c678f, 0x0005bfc9 },
+		{ 0x00000016766cb70b, 0x045edf97 },
+		{ 0x00000001fffffffb, 0x80000000 },
+		{ 0x0000000129d84b3a, 0xa2e8fe71 },
+		{ 0x0000000100000001, 0xfffffffd },
+		{ 0x0000000100000000, 0xfffffffb },
+	}, {
+		{ 0x1c71c71c71c71c71, 0x00000003 },
+		{ 0x0210842108421084, 0x0000000c },
+		{ 0x007f01fc07f01fc0, 0x000000fc },
+		{ 0x00014245eabf1f9a, 0x0000a63e },
+		{ 0x0000ffffffffffff, 0x0000fffc },
+		{ 0x00001d913cecc509, 0x0007937c },
+		{ 0x00000402c70c678f, 0x0005bfca },
+		{ 0x00000016766cb70b, 0x045edf98 },
+		{ 0x00000001fffffffc, 0x00000000 },
+		{ 0x0000000129d84b3a, 0xa2e8fe72 },
+		{ 0x0000000100000002, 0x00000000 },
+		{ 0x0000000100000000, 0xfffffffc },
+	}, {
+		{ 0x1c71c71c71c71c71, 0x00000006 },
+		{ 0x0210842108421084, 0x0000000f },
+		{ 0x007f01fc07f01fc0, 0x000000ff },
+		{ 0x00014245eabf1f9a, 0x0000a641 },
+		{ 0x0000ffffffffffff, 0x0000ffff },
+		{ 0x00001d913cecc509, 0x0007937f },
+		{ 0x00000402c70c678f, 0x0005bfcd },
+		{ 0x00000016766cb70b, 0x045edf9b },
+		{ 0x00000001fffffffc, 0x00000003 },
+		{ 0x0000000129d84b3a, 0xa2e8fe75 },
+		{ 0x0000000100000002, 0x00000003 },
+		{ 0x0000000100000001, 0x00000000 },
+	},
+};
+
+static inline bool test_div64_verify(u64 quotient, u32 remainder, int i, int j)
+{
+	return (quotient == test_div64_results[i][j].quotient &&
+		remainder == test_div64_results[i][j].remainder);
+}
+
+/*
+ * This needs to be a macro, because we don't want to rely on the compiler
+ * to do constant propagation, and `do_div' may take a different path for
+ * constants, so we do want to verify that as well.
+ */
+#define test_div64_one(dividend, divisor, i, j) ({			\
+	bool result = true;						\
+	u64 quotient;							\
+	u32 remainder;							\
+									\
+	quotient = dividend;						\
+	remainder = do_div(quotient, divisor);				\
+	if (!test_div64_verify(quotient, remainder, i, j)) {		\
+		pr_err("ERROR: %016llx / %08x => %016llx,%08x\n",	\
+		       dividend, divisor, quotient, remainder);		\
+		pr_err("ERROR: expected value              => %016llx,%08x\n",\
+		       test_div64_results[i][j].quotient,		\
+		       test_div64_results[i][j].remainder);		\
+		result = false;						\
+	}								\
+	result;								\
+})
+
+/*
+ * Run calculation for the same divisor value expressed as a constant
+ * and as a variable, so as to verify the implementation for both cases
+ * should they be handled by different code execution paths.
+ */
+static bool __init test_div64(void)
+{
+	u64 dividend;
+	int i, j;
+
+	for (i = 0; i < SIZE_DIV64_DIVIDENDS; i++) {
+		dividend = test_div64_dividends[i];
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_0, i, 0))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_1, i, 1))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_2, i, 2))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_3, i, 3))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_4, i, 4))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_5, i, 5))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_6, i, 6))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_7, i, 7))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_8, i, 8))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_9, i, 9))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_A, i, 10))
+			return false;
+		if (!test_div64_one(dividend, TEST_DIV64_DIVISOR_B, i, 11))
+			return false;
+		for (j = 0; j < SIZE_DIV64_DIVISORS; j++) {
+			if (!test_div64_one(dividend, test_div64_divisors[j],
+					    i, j))
+				return false;
+		}
+	}
+	return true;
+}
+
+static int __init test_div64_init(void)
+{
+	struct timespec64 ts, ts0, ts1;
+	int i;
+
+	pr_info("Starting 64bit/32bit division and modulo test\n");
+	ktime_get_ts64(&ts0);
+
+	for (i = 0; i < TEST_DIV64_N_ITER; i++)
+		if (!test_div64())
+			break;
+
+	ktime_get_ts64(&ts1);
+	ts = timespec64_sub(ts1, ts0);
+	pr_info("Completed 64bit/32bit division and modulo test, "
+		"%llu.%09lus elapsed\n", ts.tv_sec, ts.tv_nsec);
+
+	return 0;
+}
+
+static void __exit test_div64_exit(void)
+{
+}
+
+module_init(test_div64_init);
+module_exit(test_div64_exit);
+
+MODULE_AUTHOR("Maciej W. Rozycki <macro@orcam.me.uk>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("64bit/32bit division and modulo test module");