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, 244 insertions, 0 deletions

diff --git a/drivers/input/joystick/twidjoy.c b/drivers/input/joystick/twidjoy.c
new file mode 100644
index 000000000..fb452552c
--- /dev/null
+++ b/drivers/input/joystick/twidjoy.c
@@ -0,0 +1,244 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2001 Arndt Schoenewald
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *  Copyright (c) 2000 Mark Fletcher
+ *
+ *  Sponsored by Quelltext AG (http://www.quelltext-ag.de), Dortmund, Germany
+ */
+
+/*
+ * Driver to use Handykey's Twiddler (the first edition, i.e. the one with
+ * the RS232 interface) as a joystick under Linux
+ *
+ * The Twiddler is a one-handed chording keyboard featuring twelve buttons on
+ * the front, six buttons on the top, and a built-in tilt sensor. The buttons
+ * on the front, which are grouped as four rows of three buttons, are pressed
+ * by the four fingers (this implies only one button per row can be held down
+ * at the same time) and the buttons on the top are for the thumb. The tilt
+ * sensor delivers X and Y axis data depending on how the Twiddler is held.
+ * Additional information can be found at http://www.handykey.com.
+ *
+ * This driver does not use the Twiddler for its intended purpose, i.e. as
+ * a chording keyboard, but as a joystick: pressing and releasing a button
+ * immediately sends a corresponding button event, and tilting it generates
+ * corresponding ABS_X and ABS_Y events. This turns the Twiddler into a game
+ * controller with amazing 18 buttons :-)
+ *
+ * Note: The Twiddler2 (the successor of the Twiddler that connects directly
+ * to the PS/2 keyboard and mouse ports) is NOT supported by this driver!
+ *
+ * For questions or feedback regarding this driver module please contact:
+ * Arndt Schoenewald <arndt@quelltext.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Handykey Twiddler keyboard as a joystick driver"
+
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Constants.
+ */
+
+#define TWIDJOY_MAX_LENGTH 5
+
+static struct twidjoy_button_spec {
+	int bitshift;
+	int bitmask;
+	int buttons[3];
+}
+twidjoy_buttons[] = {
+	{  0, 3, { BTN_A,      BTN_B,     BTN_C    } },
+	{  2, 3, { BTN_X,      BTN_Y,     BTN_Z    } },
+	{  4, 3, { BTN_TL,     BTN_TR,    BTN_TR2  } },
+	{  6, 3, { BTN_SELECT, BTN_START, BTN_MODE } },
+	{  8, 1, { BTN_BASE5                       } },
+	{  9, 1, { BTN_BASE                        } },
+	{ 10, 1, { BTN_BASE3                       } },
+	{ 11, 1, { BTN_BASE4                       } },
+	{ 12, 1, { BTN_BASE2                       } },
+	{ 13, 1, { BTN_BASE6                       } },
+	{ 0,  0, { 0                               } }
+};
+
+/*
+ * Per-Twiddler data.
+ */
+
+struct twidjoy {
+	struct input_dev *dev;
+	int idx;
+	unsigned char data[TWIDJOY_MAX_LENGTH];
+	char phys[32];
+};
+
+/*
+ * twidjoy_process_packet() decodes packets the driver receives from the
+ * Twiddler. It updates the data accordingly.
+ */
+
+static void twidjoy_process_packet(struct twidjoy *twidjoy)
+{
+	struct input_dev *dev = twidjoy->dev;
+	unsigned char *data = twidjoy->data;
+	struct twidjoy_button_spec *bp;
+	int button_bits, abs_x, abs_y;
+
+	button_bits = ((data[1] & 0x7f) << 7) | (data[0] & 0x7f);
+
+	for (bp = twidjoy_buttons; bp->bitmask; bp++) {
+		int value = (button_bits & (bp->bitmask << bp->bitshift)) >> bp->bitshift;
+		int i;
+
+		for (i = 0; i < bp->bitmask; i++)
+			input_report_key(dev, bp->buttons[i], i+1 == value);
+	}
+
+	abs_x = ((data[4] & 0x07) << 5) | ((data[3] & 0x7C) >> 2);
+	if (data[4] & 0x08) abs_x -= 256;
+
+	abs_y = ((data[3] & 0x01) << 7) | ((data[2] & 0x7F) >> 0);
+	if (data[3] & 0x02) abs_y -= 256;
+
+	input_report_abs(dev, ABS_X, -abs_x);
+	input_report_abs(dev, ABS_Y, +abs_y);
+
+	input_sync(dev);
+}
+
+/*
+ * twidjoy_interrupt() is called by the low level driver when characters
+ * are ready for us. We then buffer them for further processing, or call the
+ * packet processing routine.
+ */
+
+static irqreturn_t twidjoy_interrupt(struct serio *serio, unsigned char data, unsigned int flags)
+{
+	struct twidjoy *twidjoy = serio_get_drvdata(serio);
+
+	/* All Twiddler packets are 5 bytes. The fact that the first byte
+	 * has a MSB of 0 and all other bytes have a MSB of 1 can be used
+	 * to check and regain sync. */
+
+	if ((data & 0x80) == 0)
+		twidjoy->idx = 0;	/* this byte starts a new packet */
+	else if (twidjoy->idx == 0)
+		return IRQ_HANDLED;	/* wrong MSB -- ignore this byte */
+
+	if (twidjoy->idx < TWIDJOY_MAX_LENGTH)
+		twidjoy->data[twidjoy->idx++] = data;
+
+	if (twidjoy->idx == TWIDJOY_MAX_LENGTH) {
+		twidjoy_process_packet(twidjoy);
+		twidjoy->idx = 0;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * twidjoy_disconnect() is the opposite of twidjoy_connect()
+ */
+
+static void twidjoy_disconnect(struct serio *serio)
+{
+	struct twidjoy *twidjoy = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(twidjoy->dev);
+	kfree(twidjoy);
+}
+
+/*
+ * twidjoy_connect() is the routine that is called when someone adds a
+ * new serio device. It looks for the Twiddler, and if found, registers
+ * it as an input device.
+ */
+
+static int twidjoy_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct twidjoy_button_spec *bp;
+	struct twidjoy *twidjoy;
+	struct input_dev *input_dev;
+	int err = -ENOMEM;
+	int i;
+
+	twidjoy = kzalloc_obj(*twidjoy);
+	input_dev = input_allocate_device();
+	if (!twidjoy || !input_dev)
+		goto fail1;
+
+	twidjoy->dev = input_dev;
+	snprintf(twidjoy->phys, sizeof(twidjoy->phys), "%s/input0", serio->phys);
+
+	input_dev->name = "Handykey Twiddler";
+	input_dev->phys = twidjoy->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_TWIDJOY;
+	input_dev->id.product = 0x0001;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = &serio->dev;
+
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_set_abs_params(input_dev, ABS_X, -50, 50, 4, 4);
+	input_set_abs_params(input_dev, ABS_Y, -50, 50, 4, 4);
+
+	for (bp = twidjoy_buttons; bp->bitmask; bp++)
+		for (i = 0; i < bp->bitmask; i++)
+			set_bit(bp->buttons[i], input_dev->keybit);
+
+	serio_set_drvdata(serio, twidjoy);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(twidjoy->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(twidjoy);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id twidjoy_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_TWIDJOY,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, twidjoy_serio_ids);
+
+static struct serio_driver twidjoy_drv = {
+	.driver		= {
+		.name	= "twidjoy",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= twidjoy_serio_ids,
+	.interrupt	= twidjoy_interrupt,
+	.connect	= twidjoy_connect,
+	.disconnect	= twidjoy_disconnect,
+};
+
+module_serio_driver(twidjoy_drv);