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

1 files changed, 165 insertions, 0 deletions

diff --git a/drivers/input/keyboard/ipaq-micro-keys.c b/drivers/input/keyboard/ipaq-micro-keys.c
new file mode 100644
index 000000000..ebd991de7
--- /dev/null
+++ b/drivers/input/keyboard/ipaq-micro-keys.c
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * h3600 atmel micro companion support, key subdevice
+ * based on previous kernel 2.4 version
+ * Author : Alessandro Gardich <gremlin@gremlin.it>
+ * Author : Linus Walleij <linus.walleij@linaro.org>
+ */
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/fs.h>
+#include <linux/interrupt.h>
+#include <linux/sched.h>
+#include <linux/pm.h>
+#include <linux/sysctl.h>
+#include <linux/proc_fs.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/ipaq-micro.h>
+
+static const u16 micro_keycodes[] = {
+	KEY_RECORD,		/* 1:  Record button			*/
+	KEY_CALENDAR,		/* 2:  Calendar				*/
+	KEY_ADDRESSBOOK,	/* 3:  Contacts (looks like Outlook)	*/
+	KEY_MAIL,		/* 4:  Envelope (Q on older iPAQs)	*/
+	KEY_HOMEPAGE,		/* 5:  Start (looks like swoopy arrow)	*/
+	KEY_UP,			/* 6:  Up				*/
+	KEY_RIGHT,		/* 7:  Right				*/
+	KEY_LEFT,		/* 8:  Left				*/
+	KEY_DOWN,		/* 9:  Down				*/
+};
+
+struct ipaq_micro_keys {
+	struct ipaq_micro *micro;
+	struct input_dev *input;
+	u16 codes[ARRAY_SIZE(micro_keycodes)];
+};
+
+static void micro_key_receive(void *data, int len, unsigned char *msg)
+{
+	struct ipaq_micro_keys *keys = data;
+	int key, down;
+
+	if (len < 1)
+		return;
+
+	down = 0x80 & msg[0];
+	key  = 0x7f & msg[0];
+
+	if (key < ARRAY_SIZE(micro_keycodes)) {
+		input_report_key(keys->input, keys->codes[key], down);
+		input_sync(keys->input);
+	}
+}
+
+static void micro_key_start(struct ipaq_micro_keys *keys)
+{
+	guard(spinlock_irq)(&keys->micro->lock);
+
+	keys->micro->key = micro_key_receive;
+	keys->micro->key_data = keys;
+}
+
+static void micro_key_stop(struct ipaq_micro_keys *keys)
+{
+	guard(spinlock_irq)(&keys->micro->lock);
+
+	keys->micro->key = NULL;
+	keys->micro->key_data = NULL;
+}
+
+static int micro_key_open(struct input_dev *input)
+{
+	struct ipaq_micro_keys *keys = input_get_drvdata(input);
+
+	micro_key_start(keys);
+
+	return 0;
+}
+
+static void micro_key_close(struct input_dev *input)
+{
+	struct ipaq_micro_keys *keys = input_get_drvdata(input);
+
+	micro_key_stop(keys);
+}
+
+static int micro_key_probe(struct platform_device *pdev)
+{
+	struct ipaq_micro_keys *keys;
+	int error;
+	int i;
+
+	keys = devm_kzalloc(&pdev->dev, sizeof(*keys), GFP_KERNEL);
+	if (!keys)
+		return -ENOMEM;
+
+	keys->micro = dev_get_drvdata(pdev->dev.parent);
+
+	keys->input = devm_input_allocate_device(&pdev->dev);
+	if (!keys->input)
+		return -ENOMEM;
+
+	keys->input->keycodesize = sizeof(micro_keycodes[0]);
+	keys->input->keycodemax = ARRAY_SIZE(micro_keycodes);
+	memcpy(keys->codes, micro_keycodes, sizeof(keys->codes));
+
+	keys->input->keycode = keys->codes;
+
+	__set_bit(EV_KEY, keys->input->evbit);
+	for (i = 0; i < ARRAY_SIZE(micro_keycodes); i++)
+		__set_bit(micro_keycodes[i], keys->input->keybit);
+
+	keys->input->name = "h3600 micro keys";
+	keys->input->open = micro_key_open;
+	keys->input->close = micro_key_close;
+	input_set_drvdata(keys->input, keys);
+
+	error = input_register_device(keys->input);
+	if (error)
+		return error;
+
+	platform_set_drvdata(pdev, keys);
+	return 0;
+}
+
+static int micro_key_suspend(struct device *dev)
+{
+	struct ipaq_micro_keys *keys = dev_get_drvdata(dev);
+
+	micro_key_stop(keys);
+
+	return 0;
+}
+
+static int micro_key_resume(struct device *dev)
+{
+	struct ipaq_micro_keys *keys = dev_get_drvdata(dev);
+	struct input_dev *input = keys->input;
+
+	guard(mutex)(&input->mutex);
+
+	if (input_device_enabled(input))
+		micro_key_start(keys);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(micro_key_dev_pm_ops,
+				micro_key_suspend, micro_key_resume);
+
+static struct platform_driver micro_key_device_driver = {
+	.driver = {
+		.name    = "ipaq-micro-keys",
+		.pm	= pm_sleep_ptr(&micro_key_dev_pm_ops),
+	},
+	.probe   = micro_key_probe,
+};
+module_platform_driver(micro_key_device_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("driver for iPAQ Atmel micro keys");
+MODULE_ALIAS("platform:ipaq-micro-keys");