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, 192 insertions, 0 deletions

diff --git a/drivers/input/misc/max7360-rotary.c b/drivers/input/misc/max7360-rotary.c
new file mode 100644
index 000000000..385831ef3
--- /dev/null
+++ b/drivers/input/misc/max7360-rotary.c
@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2025 Bootlin
+ *
+ * Author: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
+ */
+
+#include <linux/bitfield.h>
+#include <linux/device/devres.h>
+#include <linux/dev_printk.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/mfd/max7360.h>
+#include <linux/property.h>
+#include <linux/platform_device.h>
+#include <linux/pm_wakeirq.h>
+#include <linux/regmap.h>
+#include <linux/types.h>
+
+#define MAX7360_ROTARY_DEFAULT_STEPS 24
+
+struct max7360_rotary {
+	struct input_dev *input;
+	struct regmap *regmap;
+	unsigned int debounce_ms;
+
+	unsigned int pos;
+
+	u32 steps;
+	u32 axis;
+	bool relative_axis;
+	bool rollover;
+};
+
+static void max7360_rotary_report_event(struct max7360_rotary *max7360_rotary, int steps)
+{
+	if (max7360_rotary->relative_axis) {
+		input_report_rel(max7360_rotary->input, max7360_rotary->axis, steps);
+	} else {
+		int pos = max7360_rotary->pos;
+		int maxval = max7360_rotary->steps;
+
+		/*
+		 * Add steps to the position.
+		 * Make sure added steps are always in ]-maxval; maxval[
+		 * interval, so (pos + maxval) is always >= 0.
+		 * Then set back pos to the [0; maxval[ interval.
+		 */
+		pos += steps % maxval;
+		if (max7360_rotary->rollover)
+			pos = (pos + maxval) % maxval;
+		else
+			pos = clamp(pos, 0, maxval - 1);
+
+		max7360_rotary->pos = pos;
+		input_report_abs(max7360_rotary->input, max7360_rotary->axis, max7360_rotary->pos);
+	}
+
+	input_sync(max7360_rotary->input);
+}
+
+static irqreturn_t max7360_rotary_irq(int irq, void *data)
+{
+	struct max7360_rotary *max7360_rotary = data;
+	struct device *dev = max7360_rotary->input->dev.parent;
+	unsigned int val;
+	int error;
+
+	error = regmap_read(max7360_rotary->regmap, MAX7360_REG_RTR_CNT, &val);
+	if (error < 0) {
+		dev_err(dev, "Failed to read rotary counter\n");
+		return IRQ_NONE;
+	}
+
+	if (val == 0)
+		return IRQ_NONE;
+
+	max7360_rotary_report_event(max7360_rotary, sign_extend32(val, 7));
+
+	return IRQ_HANDLED;
+}
+
+static int max7360_rotary_hw_init(struct max7360_rotary *max7360_rotary)
+{
+	struct device *dev = max7360_rotary->input->dev.parent;
+	int val;
+	int error;
+
+	val = FIELD_PREP(MAX7360_ROT_DEBOUNCE, max7360_rotary->debounce_ms) |
+	      FIELD_PREP(MAX7360_ROT_INTCNT, 1) | MAX7360_ROT_INTCNT_DLY;
+	error = regmap_write(max7360_rotary->regmap, MAX7360_REG_RTRCFG, val);
+	if (error)
+		dev_err(dev, "Failed to set max7360 rotary encoder configuration\n");
+
+	return error;
+}
+
+static int max7360_rotary_probe(struct platform_device *pdev)
+{
+	struct max7360_rotary *max7360_rotary;
+	struct device *dev = &pdev->dev;
+	struct input_dev *input;
+	struct regmap *regmap;
+	int irq;
+	int error;
+
+	regmap = dev_get_regmap(dev->parent, NULL);
+	if (!regmap)
+		return dev_err_probe(dev, -ENODEV, "Could not get parent regmap\n");
+
+	irq = fwnode_irq_get_byname(dev_fwnode(dev->parent), "inti");
+	if (irq < 0)
+		return dev_err_probe(dev, irq, "Failed to get IRQ\n");
+
+	max7360_rotary = devm_kzalloc(dev, sizeof(*max7360_rotary), GFP_KERNEL);
+	if (!max7360_rotary)
+		return -ENOMEM;
+
+	max7360_rotary->regmap = regmap;
+
+	device_property_read_u32(dev->parent, "linux,axis", &max7360_rotary->axis);
+	max7360_rotary->rollover = device_property_read_bool(dev->parent,
+							     "rotary-encoder,rollover");
+	max7360_rotary->relative_axis =
+		device_property_read_bool(dev->parent, "rotary-encoder,relative-axis");
+
+	error = device_property_read_u32(dev->parent, "rotary-encoder,steps",
+					 &max7360_rotary->steps);
+	if (error)
+		max7360_rotary->steps = MAX7360_ROTARY_DEFAULT_STEPS;
+
+	device_property_read_u32(dev->parent, "rotary-debounce-delay-ms",
+				 &max7360_rotary->debounce_ms);
+	if (max7360_rotary->debounce_ms > MAX7360_ROT_DEBOUNCE_MAX)
+		return dev_err_probe(dev, -EINVAL, "Invalid debounce timing: %u\n",
+				     max7360_rotary->debounce_ms);
+
+	input = devm_input_allocate_device(dev);
+	if (!input)
+		return -ENOMEM;
+
+	max7360_rotary->input = input;
+
+	input->id.bustype = BUS_I2C;
+	input->name = pdev->name;
+
+	if (max7360_rotary->relative_axis)
+		input_set_capability(input, EV_REL, max7360_rotary->axis);
+	else
+		input_set_abs_params(input, max7360_rotary->axis, 0, max7360_rotary->steps, 0, 1);
+
+	error = devm_request_threaded_irq(dev, irq, NULL, max7360_rotary_irq,
+					  IRQF_ONESHOT | IRQF_SHARED,
+					  "max7360-rotary", max7360_rotary);
+	if (error)
+		return dev_err_probe(dev, error, "Failed to register interrupt\n");
+
+	error = input_register_device(input);
+	if (error)
+		return dev_err_probe(dev, error, "Could not register input device\n");
+
+	error = max7360_rotary_hw_init(max7360_rotary);
+	if (error)
+		return dev_err_probe(dev, error, "Failed to initialize max7360 rotary\n");
+
+	device_init_wakeup(dev, true);
+	error = dev_pm_set_wake_irq(dev, irq);
+	if (error)
+		dev_warn(dev, "Failed to set up wakeup irq: %d\n", error);
+
+	return 0;
+}
+
+static void max7360_rotary_remove(struct platform_device *pdev)
+{
+	dev_pm_clear_wake_irq(&pdev->dev);
+	device_init_wakeup(&pdev->dev, false);
+}
+
+static struct platform_driver max7360_rotary_driver = {
+	.driver = {
+		.name	= "max7360-rotary",
+	},
+	.probe		= max7360_rotary_probe,
+	.remove		= max7360_rotary_remove,
+};
+module_platform_driver(max7360_rotary_driver);
+
+MODULE_DESCRIPTION("MAX7360 Rotary driver");
+MODULE_AUTHOR("Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>");
+MODULE_LICENSE("GPL");