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, 169 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/gunze.c b/drivers/input/touchscreen/gunze.c
new file mode 100644
index 000000000..2baeb4f3b
--- /dev/null
+++ b/drivers/input/touchscreen/gunze.c
@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ */
+
+/*
+ * Gunze AHL-51S touchscreen driver for Linux
+ */
+
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Gunze AHL-51S touchscreen driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define	GUNZE_MAX_LENGTH	10
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct gunze {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[GUNZE_MAX_LENGTH];
+	char phys[32];
+};
+
+static void gunze_process_packet(struct gunze *gunze)
+{
+	struct input_dev *dev = gunze->dev;
+
+	if (gunze->idx != GUNZE_MAX_LENGTH || gunze->data[5] != ',' ||
+		(gunze->data[0] != 'T' && gunze->data[0] != 'R')) {
+		printk(KERN_WARNING "gunze.c: bad packet: >%.*s<\n", GUNZE_MAX_LENGTH, gunze->data);
+		return;
+	}
+
+	input_report_abs(dev, ABS_X, simple_strtoul(gunze->data + 1, NULL, 10));
+	input_report_abs(dev, ABS_Y, 1024 - simple_strtoul(gunze->data + 6, NULL, 10));
+	input_report_key(dev, BTN_TOUCH, gunze->data[0] == 'T');
+	input_sync(dev);
+}
+
+static irqreturn_t gunze_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct gunze *gunze = serio_get_drvdata(serio);
+
+	if (data == '\r') {
+		gunze_process_packet(gunze);
+		gunze->idx = 0;
+	} else {
+		if (gunze->idx < GUNZE_MAX_LENGTH)
+			gunze->data[gunze->idx++] = data;
+	}
+	return IRQ_HANDLED;
+}
+
+/*
+ * gunze_disconnect() is the opposite of gunze_connect()
+ */
+
+static void gunze_disconnect(struct serio *serio)
+{
+	struct gunze *gunze = serio_get_drvdata(serio);
+
+	input_get_device(gunze->dev);
+	input_unregister_device(gunze->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(gunze->dev);
+	kfree(gunze);
+}
+
+/*
+ * gunze_connect() is the routine that is called when someone adds a
+ * new serio device that supports Gunze protocol and registers it as
+ * an input device.
+ */
+
+static int gunze_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct gunze *gunze;
+	struct input_dev *input_dev;
+	int err;
+
+	gunze = kzalloc_obj(*gunze);
+	input_dev = input_allocate_device();
+	if (!gunze || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	gunze->serio = serio;
+	gunze->dev = input_dev;
+	scnprintf(gunze->phys, sizeof(serio->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Gunze AHL-51S TouchScreen";
+	input_dev->phys = gunze->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_GUNZE;
+	input_dev->id.product = 0x0051;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_TOUCH)] = BIT_MASK(BTN_TOUCH);
+	input_set_abs_params(input_dev, ABS_X, 24, 1000, 0, 0);
+	input_set_abs_params(input_dev, ABS_Y, 24, 1000, 0, 0);
+
+	serio_set_drvdata(serio, gunze);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(gunze->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(gunze);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id gunze_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_GUNZE,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, gunze_serio_ids);
+
+static struct serio_driver gunze_drv = {
+	.driver		= {
+		.name	= "gunze",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= gunze_serio_ids,
+	.interrupt	= gunze_interrupt,
+	.connect	= gunze_connect,
+	.disconnect	= gunze_disconnect,
+};
+
+module_serio_driver(gunze_drv);