sched/cache: Keep nr_pref_llc_running in the runnable domain, to fix LLC mis-scheduling buggrafted

alb_break_llc() decides whether to break LLC preference during active
load balance. It does so by testing that every runnable fair task on the
source rq prefers its LLC:

	env->src_rq->nr_pref_llc_running == env->src_rq->cfs.h_nr_runnable

But the two counters cover different sets. nr_pref_llc_running is updated
in account_llc_enqueue()/account_llc_dequeue(), next to cfs_rq->nr_queued,
so it follows queued tasks. h_nr_runnable is updated in set_delayed()/
clear_delayed() and drops delay-dequeued tasks.

So under DELAY_DEQUEUE, a preferring task that goes to sleep stays counted
in nr_pref_llc_running while h_nr_runnable falls. The equality then breaks,
alb_break_llc() returns false, and active balance is free to pull a task
off its preferred LLC. Active balance only moves runnable tasks, and this
is the only LLC check it consults: once the stopper runs, LBF_ACTIVE_LB
skips the per-task test in can_migrate_task(). The runnable set is the one
we want.

Fix it on the counter side. A task should be counted in
nr_pref_llc_running exactly while it is both queued on its preferred LLC
(pref_llc_queued) and runnable (!sched_delayed). Define that membership
once in task_pref_llc_runnable(), and adjust the counter only through
pref_llc_running_inc()/pref_llc_running_dec() from the four sites that
change either input: account_llc_enqueue(), account_llc_dequeue(),
set_delayed() and clear_delayed(). Gating every update on the same
predicate keeps the delay, wake and dequeue paths from double-counting
or underflowing; see the comments at those sites for the ordering.

nr_llc_running and sd->llc_counts are not touched and stay on queued
semantics.

Fixes: 714059f79ff0 ("sched/cache: Handle moving single tasks to/from their preferred LLC")
Closes: https://lore.kernel.org/lkml/20260827135000.735138-1-zhanxusheng@xiaomi.com/
Reported-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Suggested-by: Chen Yu <yu.c.chen@intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Kayra Cizmeci <kayracizmeci@gmail.com>
Cc: <stable@kernel.org> # v7.2.x
Link: https://patch.msgid.link/06af61afedac32e6477f57feb4d658f6c411c3af.1790035273.git.tim.c.chen@linux.intel.com

3 files changed, 189 insertions, 0 deletions

diff --git a/drivers/input/tests/.kunitconfig b/drivers/input/tests/.kunitconfig
new file mode 100644
index 000000000..2f5bedf80
--- /dev/null
+++ b/drivers/input/tests/.kunitconfig
@@ -0,0 +1,3 @@
+CONFIG_KUNIT=y
+CONFIG_INPUT=y
+CONFIG_INPUT_KUNIT_TEST=y
diff --git a/drivers/input/tests/Makefile b/drivers/input/tests/Makefile
new file mode 100644
index 000000000..90cf95418
--- /dev/null
+++ b/drivers/input/tests/Makefile
@@ -0,0 +1,3 @@
+# SPDX-License-Identifier: GPL-2.0
+
+obj-$(CONFIG_INPUT_KUNIT_TEST) += input_test.o
diff --git a/drivers/input/tests/input_test.c b/drivers/input/tests/input_test.c
new file mode 100644
index 000000000..e105ce71a
--- /dev/null
+++ b/drivers/input/tests/input_test.c
@@ -0,0 +1,183 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for the input core.
+ *
+ * Copyright (c) 2023 Red Hat Inc
+ */
+
+#include <linux/delay.h>
+#include <linux/input.h>
+
+#include <kunit/test.h>
+
+#define POLL_INTERVAL 100
+
+static int input_test_init(struct kunit *test)
+{
+	struct input_dev *input_dev;
+	int ret;
+
+	input_dev = input_allocate_device();
+	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, input_dev);
+
+	input_dev->name = "Test input device";
+	input_dev->id.bustype = BUS_VIRTUAL;
+	input_dev->id.vendor = 1;
+	input_dev->id.product = 1;
+	input_dev->id.version = 1;
+	input_set_capability(input_dev, EV_KEY, BTN_LEFT);
+	input_set_capability(input_dev, EV_KEY, BTN_RIGHT);
+
+	ret = input_register_device(input_dev);
+	if (ret) {
+		input_free_device(input_dev);
+		KUNIT_FAIL_AND_ABORT(test, "Register device failed: %d", ret);
+	}
+
+	test->priv = input_dev;
+
+	return 0;
+}
+
+static void input_test_exit(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+
+	if (input_dev)
+		input_unregister_device(input_dev);
+}
+
+static void input_test_poll(struct input_dev *input) { }
+
+static void input_test_polling(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+
+	/* Must fail because a poll handler has not been set-up yet */
+	KUNIT_ASSERT_EQ(test, input_get_poll_interval(input_dev), -EINVAL);
+
+	KUNIT_ASSERT_EQ(test, input_setup_polling(input_dev, input_test_poll), 0);
+
+	input_set_poll_interval(input_dev, POLL_INTERVAL);
+
+	/* Must succeed because poll handler was set-up and poll interval set */
+	KUNIT_ASSERT_EQ(test, input_get_poll_interval(input_dev), POLL_INTERVAL);
+}
+
+static void input_test_timestamp(struct kunit *test)
+{
+	const ktime_t invalid_timestamp = ktime_set(0, 0);
+	struct input_dev *input_dev = test->priv;
+	ktime_t *timestamp, time;
+
+	timestamp = input_get_timestamp(input_dev);
+	time = timestamp[INPUT_CLK_MONO];
+
+	/* The returned timestamp must always be valid */
+	KUNIT_ASSERT_EQ(test, ktime_compare(time, invalid_timestamp), 1);
+
+	time = ktime_get();
+	input_set_timestamp(input_dev, time);
+
+	timestamp = input_get_timestamp(input_dev);
+	/* The timestamp must be the same than set before */
+	KUNIT_ASSERT_EQ(test, ktime_compare(timestamp[INPUT_CLK_MONO], time), 0);
+}
+
+static void input_test_match_device_id(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+	struct input_device_id id = { 0 };
+
+	/*
+	 * Must match when the input device bus, vendor, product, version
+	 * and events capable of handling are the same and fail to match
+	 * otherwise.
+	 */
+	id.flags = INPUT_DEVICE_ID_MATCH_BUS;
+	id.bustype = BUS_VIRTUAL;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.bustype = BUS_I2C;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_VENDOR;
+	id.vendor = 1;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.vendor = 2;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_PRODUCT;
+	id.product = 1;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.product = 2;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_VERSION;
+	id.version = 1;
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	id.version = 2;
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+
+	id.flags = INPUT_DEVICE_ID_MATCH_EVBIT;
+	__set_bit(EV_KEY, id.evbit);
+	KUNIT_ASSERT_TRUE(test, input_match_device_id(input_dev, &id));
+
+	__set_bit(EV_ABS, id.evbit);
+	KUNIT_ASSERT_FALSE(test, input_match_device_id(input_dev, &id));
+}
+
+static void input_test_grab(struct kunit *test)
+{
+	struct input_dev *input_dev = test->priv;
+	struct input_handle test_handle;
+	struct input_handler handler;
+	struct input_handle handle;
+	struct input_device_id id;
+	int res;
+
+	handler.name = "handler";
+	handler.id_table = &id;
+
+	handle.dev = input_get_device(input_dev);
+	handle.name = dev_name(&input_dev->dev);
+	handle.handler = &handler;
+	res = input_grab_device(&handle);
+	KUNIT_ASSERT_TRUE(test, res == 0);
+
+	test_handle.dev = input_get_device(input_dev);
+	test_handle.name = dev_name(&input_dev->dev);
+	test_handle.handler = &handler;
+	res = input_grab_device(&test_handle);
+	KUNIT_ASSERT_EQ(test, res, -EBUSY);
+
+	input_release_device(&handle);
+	input_put_device(input_dev);
+	res = input_grab_device(&test_handle);
+	KUNIT_ASSERT_TRUE(test, res == 0);
+	input_put_device(input_dev);
+}
+
+static struct kunit_case input_tests[] = {
+	KUNIT_CASE(input_test_polling),
+	KUNIT_CASE(input_test_timestamp),
+	KUNIT_CASE(input_test_match_device_id),
+	KUNIT_CASE(input_test_grab),
+	{ /* sentinel */ }
+};
+
+static struct kunit_suite input_test_suite = {
+	.name = "input_core",
+	.init = input_test_init,
+	.exit = input_test_exit,
+	.test_cases = input_tests,
+};
+
+kunit_test_suite(input_test_suite);
+
+MODULE_AUTHOR("Javier Martinez Canillas <javierm@redhat.com>");
+MODULE_DESCRIPTION("KUnit test for the input core");
+MODULE_LICENSE("GPL");