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, 188 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/inexio.c b/drivers/input/touchscreen/inexio.c
new file mode 100644
index 000000000..2fa04eaec
--- /dev/null
+++ b/drivers/input/touchscreen/inexio.c
@@ -0,0 +1,188 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * iNexio serial touchscreen driver
+ *
+ * Copyright (c) 2008 Richard Lemon
+ * Based on the mtouch driver (c) Vojtech Pavlik and Dan Streetman
+ */
+
+
+/*
+ * 2008/06/19 Richard Lemon <richard@codelemon.com>
+ *   Copied mtouch.c and edited for iNexio protocol
+ */
+
+#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	"iNexio serial touchscreen driver"
+
+MODULE_AUTHOR("Richard Lemon <richard@codelemon.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define INEXIO_FORMAT_TOUCH_BIT 0x01
+#define INEXIO_FORMAT_LENGTH 5
+#define INEXIO_RESPONSE_BEGIN_BYTE 0x80
+
+/* todo: check specs for max length of all responses */
+#define INEXIO_MAX_LENGTH 16
+
+#define INEXIO_MIN_XC 0
+#define INEXIO_MAX_XC 0x3fff
+#define INEXIO_MIN_YC 0
+#define INEXIO_MAX_YC 0x3fff
+
+#define INEXIO_GET_XC(data) (((data[1])<<7) | data[2])
+#define INEXIO_GET_YC(data) (((data[3])<<7) | data[4])
+#define INEXIO_GET_TOUCHED(data) (INEXIO_FORMAT_TOUCH_BIT & data[0])
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct inexio {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[INEXIO_MAX_LENGTH];
+	char phys[32];
+};
+
+static void inexio_process_data(struct inexio *pinexio)
+{
+	struct input_dev *dev = pinexio->dev;
+
+	if (INEXIO_FORMAT_LENGTH == ++pinexio->idx) {
+		input_report_abs(dev, ABS_X, INEXIO_GET_XC(pinexio->data));
+		input_report_abs(dev, ABS_Y, INEXIO_GET_YC(pinexio->data));
+		input_report_key(dev, BTN_TOUCH, INEXIO_GET_TOUCHED(pinexio->data));
+		input_sync(dev);
+
+		pinexio->idx = 0;
+	}
+}
+
+static irqreturn_t inexio_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct inexio *pinexio = serio_get_drvdata(serio);
+
+	pinexio->data[pinexio->idx] = data;
+
+	if (INEXIO_RESPONSE_BEGIN_BYTE&pinexio->data[0])
+		inexio_process_data(pinexio);
+	else
+		dev_dbg(&serio->dev,
+			"unknown/unsynchronized data from device, byte %x\n",
+			pinexio->data[0]);
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * inexio_disconnect() is the opposite of inexio_connect()
+ */
+
+static void inexio_disconnect(struct serio *serio)
+{
+	struct inexio *pinexio = serio_get_drvdata(serio);
+
+	input_get_device(pinexio->dev);
+	input_unregister_device(pinexio->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(pinexio->dev);
+	kfree(pinexio);
+}
+
+/*
+ * inexio_connect() is the routine that is called when someone adds a
+ * new serio device that supports iNexio protocol and registers it as
+ * an input device. This is usually accomplished using inputattach.
+ */
+
+static int inexio_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct inexio *pinexio;
+	struct input_dev *input_dev;
+	int err;
+
+	pinexio = kzalloc_obj(*pinexio);
+	input_dev = input_allocate_device();
+	if (!pinexio || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	pinexio->serio = serio;
+	pinexio->dev = input_dev;
+	scnprintf(pinexio->phys, sizeof(pinexio->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "iNexio Serial TouchScreen";
+	input_dev->phys = pinexio->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_INEXIO;
+	input_dev->id.product = 0;
+	input_dev->id.version = 0x0001;
+	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(pinexio->dev, ABS_X, INEXIO_MIN_XC, INEXIO_MAX_XC, 0, 0);
+	input_set_abs_params(pinexio->dev, ABS_Y, INEXIO_MIN_YC, INEXIO_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, pinexio);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(pinexio->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(pinexio);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id inexio_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_INEXIO,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, inexio_serio_ids);
+
+static struct serio_driver inexio_drv = {
+	.driver		= {
+		.name	= "inexio",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= inexio_serio_ids,
+	.interrupt	= inexio_interrupt,
+	.connect	= inexio_connect,
+	.disconnect	= inexio_disconnect,
+};
+
+module_serio_driver(inexio_drv);