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, 184 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/hampshire.c b/drivers/input/touchscreen/hampshire.c
new file mode 100644
index 000000000..394ae8c88
--- /dev/null
+++ b/drivers/input/touchscreen/hampshire.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Hampshire serial touchscreen driver
+ *
+ * Copyright (c) 2010 Adam Bennett
+ * Based on the dynapro driver (c) Tias Guns
+ */
+
+
+/*
+ * 2010/04/08 Adam Bennett <abennett72@gmail.com>
+ *   Copied dynapro.c and edited for Hampshire 4-byte 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	"Hampshire serial touchscreen driver"
+
+MODULE_AUTHOR("Adam Bennett <abennett72@gmail.com>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Definitions & global arrays.
+ */
+
+#define HAMPSHIRE_FORMAT_TOUCH_BIT 0x40
+#define HAMPSHIRE_FORMAT_LENGTH 4
+#define HAMPSHIRE_RESPONSE_BEGIN_BYTE 0x80
+
+#define HAMPSHIRE_MIN_XC 0
+#define HAMPSHIRE_MAX_XC 0x1000
+#define HAMPSHIRE_MIN_YC 0
+#define HAMPSHIRE_MAX_YC 0x1000
+
+#define HAMPSHIRE_GET_XC(data) (((data[3] & 0x0c) >> 2) | (data[1] << 2) | ((data[0] & 0x38) << 6))
+#define HAMPSHIRE_GET_YC(data) ((data[3] & 0x03) | (data[2] << 2) | ((data[0] & 0x07) << 9))
+#define HAMPSHIRE_GET_TOUCHED(data) (HAMPSHIRE_FORMAT_TOUCH_BIT & data[0])
+
+/*
+ * Per-touchscreen data.
+ */
+
+struct hampshire {
+	struct input_dev *dev;
+	struct serio *serio;
+	int idx;
+	unsigned char data[HAMPSHIRE_FORMAT_LENGTH];
+	char phys[32];
+};
+
+static void hampshire_process_data(struct hampshire *phampshire)
+{
+	struct input_dev *dev = phampshire->dev;
+
+	if (HAMPSHIRE_FORMAT_LENGTH == ++phampshire->idx) {
+		input_report_abs(dev, ABS_X, HAMPSHIRE_GET_XC(phampshire->data));
+		input_report_abs(dev, ABS_Y, HAMPSHIRE_GET_YC(phampshire->data));
+		input_report_key(dev, BTN_TOUCH,
+				 HAMPSHIRE_GET_TOUCHED(phampshire->data));
+		input_sync(dev);
+
+		phampshire->idx = 0;
+	}
+}
+
+static irqreturn_t hampshire_interrupt(struct serio *serio,
+		unsigned char data, unsigned int flags)
+{
+	struct hampshire *phampshire = serio_get_drvdata(serio);
+
+	phampshire->data[phampshire->idx] = data;
+
+	if (HAMPSHIRE_RESPONSE_BEGIN_BYTE & phampshire->data[0])
+		hampshire_process_data(phampshire);
+	else
+		dev_dbg(&serio->dev, "unknown/unsynchronized data: %x\n",
+			phampshire->data[0]);
+
+	return IRQ_HANDLED;
+}
+
+static void hampshire_disconnect(struct serio *serio)
+{
+	struct hampshire *phampshire = serio_get_drvdata(serio);
+
+	input_get_device(phampshire->dev);
+	input_unregister_device(phampshire->dev);
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_put_device(phampshire->dev);
+	kfree(phampshire);
+}
+
+/*
+ * hampshire_connect() is the routine that is called when someone adds a
+ * new serio device that supports hampshire protocol and registers it as
+ * an input device. This is usually accomplished using inputattach.
+ */
+
+static int hampshire_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct hampshire *phampshire;
+	struct input_dev *input_dev;
+	int err;
+
+	phampshire = kzalloc_obj(*phampshire);
+	input_dev = input_allocate_device();
+	if (!phampshire || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	phampshire->serio = serio;
+	phampshire->dev = input_dev;
+	scnprintf(phampshire->phys, sizeof(phampshire->phys),
+		  "%s/input0", serio->phys);
+
+	input_dev->name = "Hampshire Serial TouchScreen";
+	input_dev->phys = phampshire->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_HAMPSHIRE;
+	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(phampshire->dev, ABS_X,
+			     HAMPSHIRE_MIN_XC, HAMPSHIRE_MAX_XC, 0, 0);
+	input_set_abs_params(phampshire->dev, ABS_Y,
+			     HAMPSHIRE_MIN_YC, HAMPSHIRE_MAX_YC, 0, 0);
+
+	serio_set_drvdata(serio, phampshire);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(phampshire->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(phampshire);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id hampshire_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_HAMPSHIRE,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, hampshire_serio_ids);
+
+static struct serio_driver hampshire_drv = {
+	.driver		= {
+		.name	= "hampshire",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= hampshire_serio_ids,
+	.interrupt	= hampshire_interrupt,
+	.connect	= hampshire_connect,
+	.disconnect	= hampshire_disconnect,
+};
+
+module_serio_driver(hampshire_drv);