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, 191 insertions, 0 deletions

diff --git a/drivers/input/joystick/stinger.c b/drivers/input/joystick/stinger.c
new file mode 100644
index 000000000..011f9b137
--- /dev/null
+++ b/drivers/input/joystick/stinger.c
@@ -0,0 +1,191 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *  Copyright (c) 2000 Mark Fletcher
+ */
+
+/*
+ * Gravis Stinger gamepad driver for Linux
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/input.h>
+#include <linux/serio.h>
+
+#define DRIVER_DESC	"Gravis Stinger gamepad driver"
+
+MODULE_AUTHOR("Vojtech Pavlik <vojtech@ucw.cz>");
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+/*
+ * Constants.
+ */
+
+#define STINGER_MAX_LENGTH 8
+
+/*
+ * Per-Stinger data.
+ */
+
+struct stinger {
+	struct input_dev *dev;
+	int idx;
+	unsigned char data[STINGER_MAX_LENGTH];
+	char phys[32];
+};
+
+/*
+ * stinger_process_packet() decodes packets the driver receives from the
+ * Stinger. It updates the data accordingly.
+ */
+
+static void stinger_process_packet(struct stinger *stinger)
+{
+	struct input_dev *dev = stinger->dev;
+	unsigned char *data = stinger->data;
+
+	if (!stinger->idx) return;
+
+	input_report_key(dev, BTN_A,	  ((data[0] & 0x20) >> 5));
+	input_report_key(dev, BTN_B,	  ((data[0] & 0x10) >> 4));
+	input_report_key(dev, BTN_C,	  ((data[0] & 0x08) >> 3));
+	input_report_key(dev, BTN_X,	  ((data[0] & 0x04) >> 2));
+	input_report_key(dev, BTN_Y,	  ((data[3] & 0x20) >> 5));
+	input_report_key(dev, BTN_Z,	  ((data[3] & 0x10) >> 4));
+	input_report_key(dev, BTN_TL,     ((data[3] & 0x08) >> 3));
+	input_report_key(dev, BTN_TR,     ((data[3] & 0x04) >> 2));
+	input_report_key(dev, BTN_SELECT, ((data[3] & 0x02) >> 1));
+	input_report_key(dev, BTN_START,   (data[3] & 0x01));
+
+	input_report_abs(dev, ABS_X, (data[1] & 0x3F) - ((data[0] & 0x01) << 6));
+	input_report_abs(dev, ABS_Y, ((data[0] & 0x02) << 5) - (data[2] & 0x3F));
+
+	input_sync(dev);
+
+	return;
+}
+
+/*
+ * stinger_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 stinger_interrupt(struct serio *serio,
+	unsigned char data, unsigned int flags)
+{
+	struct stinger *stinger = serio_get_drvdata(serio);
+
+	/* All Stinger packets are 4 bytes */
+
+	if (stinger->idx < STINGER_MAX_LENGTH)
+		stinger->data[stinger->idx++] = data;
+
+	if (stinger->idx == 4) {
+		stinger_process_packet(stinger);
+		stinger->idx = 0;
+	}
+
+	return IRQ_HANDLED;
+}
+
+/*
+ * stinger_disconnect() is the opposite of stinger_connect()
+ */
+
+static void stinger_disconnect(struct serio *serio)
+{
+	struct stinger *stinger = serio_get_drvdata(serio);
+
+	serio_close(serio);
+	serio_set_drvdata(serio, NULL);
+	input_unregister_device(stinger->dev);
+	kfree(stinger);
+}
+
+/*
+ * stinger_connect() is the routine that is called when someone adds a
+ * new serio device that supports Stinger protocol and registers it as
+ * an input device.
+ */
+
+static int stinger_connect(struct serio *serio, struct serio_driver *drv)
+{
+	struct stinger *stinger;
+	struct input_dev *input_dev;
+	int err = -ENOMEM;
+
+	stinger = kmalloc_obj(*stinger);
+	input_dev = input_allocate_device();
+	if (!stinger || !input_dev)
+		goto fail1;
+
+	stinger->dev = input_dev;
+	snprintf(stinger->phys, sizeof(stinger->phys), "%s/serio0", serio->phys);
+
+	input_dev->name = "Gravis Stinger";
+	input_dev->phys = stinger->phys;
+	input_dev->id.bustype = BUS_RS232;
+	input_dev->id.vendor = SERIO_STINGER;
+	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_dev->keybit[BIT_WORD(BTN_A)] = BIT_MASK(BTN_A) | BIT_MASK(BTN_B) |
+		BIT_MASK(BTN_C) | BIT_MASK(BTN_X) | BIT_MASK(BTN_Y) |
+		BIT_MASK(BTN_Z) | BIT_MASK(BTN_TL) | BIT_MASK(BTN_TR) |
+		BIT_MASK(BTN_START) | BIT_MASK(BTN_SELECT);
+	input_set_abs_params(input_dev, ABS_X, -64, 64, 0, 4);
+	input_set_abs_params(input_dev, ABS_Y, -64, 64, 0, 4);
+
+	serio_set_drvdata(serio, stinger);
+
+	err = serio_open(serio, drv);
+	if (err)
+		goto fail2;
+
+	err = input_register_device(stinger->dev);
+	if (err)
+		goto fail3;
+
+	return 0;
+
+ fail3:	serio_close(serio);
+ fail2:	serio_set_drvdata(serio, NULL);
+ fail1:	input_free_device(input_dev);
+	kfree(stinger);
+	return err;
+}
+
+/*
+ * The serio driver structure.
+ */
+
+static const struct serio_device_id stinger_serio_ids[] = {
+	{
+		.type	= SERIO_RS232,
+		.proto	= SERIO_STINGER,
+		.id	= SERIO_ANY,
+		.extra	= SERIO_ANY,
+	},
+	{ 0 }
+};
+
+MODULE_DEVICE_TABLE(serio, stinger_serio_ids);
+
+static struct serio_driver stinger_drv = {
+	.driver		= {
+		.name	= "stinger",
+	},
+	.description	= DRIVER_DESC,
+	.id_table	= stinger_serio_ids,
+	.interrupt	= stinger_interrupt,
+	.connect	= stinger_connect,
+	.disconnect	= stinger_disconnect,
+};
+
+module_serio_driver(stinger_drv);