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, 150 insertions, 0 deletions

diff --git a/drivers/input/mouse/amimouse.c b/drivers/input/mouse/amimouse.c
new file mode 100644
index 000000000..d203c2a6c
--- /dev/null
+++ b/drivers/input/mouse/amimouse.c
@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Amiga mouse driver for Linux/m68k
+ *
+ *  Copyright (c) 2000-2002 Vojtech Pavlik
+ *
+ *  Based on the work of:
+ *	Michael Rausch		James Banks
+ *	Matther Dillon		David Giller
+ *	Nathan Laredo		Linus Torvalds
+ *	Johan Myreen		Jes Sorensen
+ *	Russell King
+ */
+
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/platform_device.h>
+
+#include <asm/irq.h>
+#include <asm/setup.h>
+#include <linux/uaccess.h>
+#include <asm/amigahw.h>
+#include <asm/amigaints.h>
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION("Amiga mouse driver");
+MODULE_LICENSE("GPL");
+
+static int amimouse_lastx, amimouse_lasty;
+
+static irqreturn_t amimouse_interrupt(int irq, void *data)
+{
+	struct input_dev *dev = data;
+	unsigned short joy0dat, potgor;
+	int nx, ny, dx, dy;
+
+	joy0dat = amiga_custom.joy0dat;
+
+	nx = joy0dat & 0xff;
+	ny = joy0dat >> 8;
+
+	dx = nx - amimouse_lastx;
+	dy = ny - amimouse_lasty;
+
+	if (dx < -127) dx = (256 + nx) - amimouse_lastx;
+	if (dx >  127) dx = (nx - 256) - amimouse_lastx;
+	if (dy < -127) dy = (256 + ny) - amimouse_lasty;
+	if (dy >  127) dy = (ny - 256) - amimouse_lasty;
+
+	amimouse_lastx = nx;
+	amimouse_lasty = ny;
+
+	potgor = amiga_custom.potgor;
+
+	input_report_rel(dev, REL_X, dx);
+	input_report_rel(dev, REL_Y, dy);
+
+	input_report_key(dev, BTN_LEFT,   ciaa.pra & 0x40);
+	input_report_key(dev, BTN_MIDDLE, potgor & 0x0100);
+	input_report_key(dev, BTN_RIGHT,  potgor & 0x0400);
+
+	input_sync(dev);
+
+	return IRQ_HANDLED;
+}
+
+static int amimouse_open(struct input_dev *dev)
+{
+	unsigned short joy0dat;
+	int error;
+
+	joy0dat = amiga_custom.joy0dat;
+
+	amimouse_lastx = joy0dat & 0xff;
+	amimouse_lasty = joy0dat >> 8;
+
+	error = request_irq(IRQ_AMIGA_VERTB, amimouse_interrupt, 0, "amimouse",
+			    dev);
+	if (error)
+		dev_err(&dev->dev, "Can't allocate irq %d\n", IRQ_AMIGA_VERTB);
+
+	return error;
+}
+
+static void amimouse_close(struct input_dev *dev)
+{
+	free_irq(IRQ_AMIGA_VERTB, dev);
+}
+
+static int __init amimouse_probe(struct platform_device *pdev)
+{
+	int err;
+	struct input_dev *dev;
+
+	dev = input_allocate_device();
+	if (!dev)
+		return -ENOMEM;
+
+	dev->name = pdev->name;
+	dev->phys = "amimouse/input0";
+	dev->id.bustype = BUS_AMIGA;
+	dev->id.vendor = 0x0001;
+	dev->id.product = 0x0002;
+	dev->id.version = 0x0100;
+
+	dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_REL);
+	dev->relbit[0] = BIT_MASK(REL_X) | BIT_MASK(REL_Y);
+	dev->keybit[BIT_WORD(BTN_LEFT)] = BIT_MASK(BTN_LEFT) |
+		BIT_MASK(BTN_MIDDLE) | BIT_MASK(BTN_RIGHT);
+	dev->open = amimouse_open;
+	dev->close = amimouse_close;
+	dev->dev.parent = &pdev->dev;
+
+	err = input_register_device(dev);
+	if (err) {
+		input_free_device(dev);
+		return err;
+	}
+
+	platform_set_drvdata(pdev, dev);
+
+	return 0;
+}
+
+static void __exit amimouse_remove(struct platform_device *pdev)
+{
+	struct input_dev *dev = platform_get_drvdata(pdev);
+
+	input_unregister_device(dev);
+}
+
+/*
+ * amimouse_remove() lives in .exit.text. For drivers registered via
+ * module_platform_driver_probe() this is ok because they cannot get unbound at
+ * runtime. So mark the driver struct with __refdata to prevent modpost
+ * triggering a section mismatch warning.
+ */
+static struct platform_driver amimouse_driver __refdata = {
+	.remove = __exit_p(amimouse_remove),
+	.driver   = {
+		.name	= "amiga-mouse",
+	},
+};
+
+module_platform_driver_probe(amimouse_driver, amimouse_probe);
+
+MODULE_ALIAS("platform:amiga-mouse");