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, 112 insertions, 0 deletions

diff --git a/drivers/input/misc/cpcap-pwrbutton.c b/drivers/input/misc/cpcap-pwrbutton.c
new file mode 100644
index 000000000..85cddb847
--- /dev/null
+++ b/drivers/input/misc/cpcap-pwrbutton.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * CPCAP Power Button Input Driver
+ *
+ * Copyright (C) 2017 Sebastian Reichel <sre@kernel.org>
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/regmap.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/motorola-cpcap.h>
+
+#define CPCAP_IRQ_ON 23
+#define CPCAP_IRQ_ON_BITMASK (1 << (CPCAP_IRQ_ON % 16))
+
+struct cpcap_power_button {
+	struct regmap *regmap;
+	struct input_dev *idev;
+	struct device *dev;
+};
+
+static irqreturn_t powerbutton_irq(int irq, void *_button)
+{
+	struct cpcap_power_button *button = _button;
+	int val;
+
+	val = cpcap_sense_virq(button->regmap, irq);
+	if (val < 0) {
+		dev_err(button->dev, "irq read failed: %d", val);
+		return IRQ_HANDLED;
+	}
+
+	pm_wakeup_event(button->dev, 0);
+	input_report_key(button->idev, KEY_POWER, val);
+	input_sync(button->idev);
+
+	return IRQ_HANDLED;
+}
+
+static int cpcap_power_button_probe(struct platform_device *pdev)
+{
+	struct cpcap_power_button *button;
+	int irq;
+	int err;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	button = devm_kmalloc(&pdev->dev, sizeof(*button), GFP_KERNEL);
+	if (!button)
+		return -ENOMEM;
+
+	button->idev = devm_input_allocate_device(&pdev->dev);
+	if (!button->idev)
+		return -ENOMEM;
+
+	button->regmap = dev_get_regmap(pdev->dev.parent, NULL);
+	if (!button->regmap)
+		return -ENODEV;
+
+	button->dev = &pdev->dev;
+
+	button->idev->name = "cpcap-pwrbutton";
+	button->idev->phys = "cpcap-pwrbutton/input0";
+	input_set_capability(button->idev, EV_KEY, KEY_POWER);
+
+	err = devm_request_threaded_irq(&pdev->dev, irq, NULL,
+		powerbutton_irq, IRQF_ONESHOT, "cpcap_pwrbutton", button);
+	if (err < 0) {
+		dev_err(&pdev->dev, "IRQ request failed: %d\n", err);
+		return err;
+	}
+
+	err = input_register_device(button->idev);
+	if (err) {
+		dev_err(&pdev->dev, "Input register failed: %d\n", err);
+		return err;
+	}
+
+	device_init_wakeup(&pdev->dev, true);
+
+	return 0;
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id cpcap_pwrbutton_dt_match_table[] = {
+	{ .compatible = "motorola,cpcap-pwrbutton" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, cpcap_pwrbutton_dt_match_table);
+#endif
+
+static struct platform_driver cpcap_power_button_driver = {
+	.probe		= cpcap_power_button_probe,
+	.driver		= {
+		.name	= "cpcap-pwrbutton",
+		.of_match_table = of_match_ptr(cpcap_pwrbutton_dt_match_table),
+	},
+};
+module_platform_driver(cpcap_power_button_driver);
+
+MODULE_ALIAS("platform:cpcap-pwrbutton");
+MODULE_DESCRIPTION("CPCAP Power Button");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Sebastian Reichel <sre@kernel.org>");