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, 152 insertions, 0 deletions

diff --git a/drivers/input/keyboard/xtkbd.c b/drivers/input/keyboard/xtkbd.c
new file mode 100644
index 000000000..c0b4978a8
--- /dev/null
+++ b/drivers/input/keyboard/xtkbd.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 1999-2001 Vojtech Pavlik
+ */
+
+/*
+ * XT keyboard driver for Linux
+ */
+
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"XT keyboard driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define XTKBD_EMUL0	0xe0
+#define XTKBD_EMUL1	0xe1
+#define XTKBD_KEY	0x7f
+#define XTKBD_RELEASE	0x80
+
+static unsigned char xtkbd_keycode[256] = {
+	  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15,
+	 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
+	 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
+	 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63,
+	 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
+	 80, 81, 82, 83,  0,  0,  0, 87, 88,  0,  0,  0,  0,  0,  0,  0,
+	  0,  0,  0,  0,  0, 87, 88,  0,  0,  0,  0,110,111,103,108,105,
+	106
+};
+
+struct xtkbd {
+	unsigned char keycode[256];
+	struct input_dev *dev;
+	struct serio *serio;
+	char phys[32];
+};
+
+static irqreturn_t xtkbd_interrupt(struct serio *serio,
+	unsigned char data, unsigned int flags)
+{
+	struct xtkbd *xtkbd = serio_get_drvdata(serio);
+
+	switch (data) {
+		case XTKBD_EMUL0:
+		case XTKBD_EMUL1:
+			break;
+		default:
+
+			if (xtkbd->keycode[data & XTKBD_KEY]) {
+				input_report_key(xtkbd->dev, xtkbd->keycode[data & XTKBD_KEY], !(data & XTKBD_RELEASE));
+				input_sync(xtkbd->dev);
+			} else {
+				printk(KERN_WARNING "xtkbd.c: Unknown key (scancode %#x) %s.\n",
+					data & XTKBD_KEY, data & XTKBD_RELEASE ? "released" : "pressed");
+			}
+	}
+	return IRQ_HANDLED;
+}
+
+static int xtkbd_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct xtkbd *xtkbd;
+	struct input_dev *input_dev;
+	int err = -ENOMEM;
+	int i;
+
+	xtkbd = kmalloc_obj(*xtkbd);
+	input_dev = input_allocate_device();
+	if (!xtkbd || !input_dev)
+		goto fail1;
+
+	xtkbd->serio = serio;
+	xtkbd->dev = input_dev;
+	snprintf(xtkbd->phys, sizeof(xtkbd->phys), "%s/input0", serio->phys);
+	memcpy(xtkbd->keycode, xtkbd_keycode, sizeof(xtkbd->keycode));
+
+	input_dev->name = "XT Keyboard";
+	input_dev->phys = xtkbd->phys;
+	input_dev->id.bustype = BUS_XTKBD;
+	input_dev->id.vendor  = 0x0001;
+	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_REP);
+	input_dev->keycode = xtkbd->keycode;
+	input_dev->keycodesize = sizeof(unsigned char);
+	input_dev->keycodemax = ARRAY_SIZE(xtkbd_keycode);
+
+	for (i = 0; i < 255; i++)
+		set_bit(xtkbd->keycode[i], input_dev->keybit);
+	clear_bit(0, input_dev->keybit);
+
+	serio_set_drvdata(serio, xtkbd);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(xtkbd->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(xtkbd);
+	return err;
+}
+
+static void xtkbd_disconnect(struct serio *serio)
+{
+	struct xtkbd *xtkbd = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(xtkbd->dev);
+	kfree(xtkbd);
+}
+
+static const struct serio_device_id xtkbd_serio_ids[] = {
+	{
+		.type	= SERIO_XT,
+		.proto	= SERIO_ANY,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, xtkbd_serio_ids);
+
+static struct serio_driver xtkbd_drv = {
+	.driver		= {
+		.name	= "xtkbd",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= xtkbd_serio_ids,
+	.interrupt	= xtkbd_interrupt,
+	.connect	= xtkbd_connect,
+	.disconnect	= xtkbd_disconnect,
+};
+
+module_serio_driver(xtkbd_drv);