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, 156 insertions, 0 deletions

diff --git a/drivers/input/keyboard/dlink-dir685-touchkeys.c b/drivers/input/keyboard/dlink-dir685-touchkeys.c
new file mode 100644
index 000000000..bf94367f6
--- /dev/null
+++ b/drivers/input/keyboard/dlink-dir685-touchkeys.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * D-Link DIR-685 router I2C-based Touchkeys input driver
+ * Copyright (C) 2017 Linus Walleij <linus.walleij@linaro.org>
+ *
+ * This is a one-off touchkey controller based on the Cypress Semiconductor
+ * CY8C214 MCU with some firmware in its internal 8KB flash. The circuit
+ * board inside the router is named E119921
+ */
+
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/interrupt.h>
+#include <linux/delay.h>
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/string_choices.h>
+#include <linux/bitops.h>
+
+struct dir685_touchkeys {
+	struct device		*dev;
+	struct i2c_client	*client;
+	struct input_dev	*input;
+	unsigned long		cur_key;
+	u16			codes[7];
+};
+
+static irqreturn_t dir685_tk_irq_thread(int irq, void *data)
+{
+	struct dir685_touchkeys *tk = data;
+	const int num_bits = min_t(int, ARRAY_SIZE(tk->codes), 16);
+	unsigned long changed;
+	u8 buf[6];
+	unsigned long key;
+	int i;
+	int err;
+
+	memset(buf, 0, sizeof(buf));
+	err = i2c_master_recv(tk->client, buf, sizeof(buf));
+	if (err != sizeof(buf)) {
+		dev_err(tk->dev, "short read %d\n", err);
+		return IRQ_HANDLED;
+	}
+
+	dev_dbg(tk->dev, "IN: %*ph\n", (int)sizeof(buf), buf);
+	key = be16_to_cpup((__be16 *) &buf[4]);
+
+	/* Figure out if any bits went high or low since last message */
+	changed = tk->cur_key ^ key;
+	for_each_set_bit(i, &changed, num_bits) {
+		dev_dbg(tk->dev, "key %d is %s\n", i,
+			str_down_up(test_bit(i, &key)));
+		input_report_key(tk->input, tk->codes[i], test_bit(i, &key));
+	}
+
+	/* Store currently down keys */
+	tk->cur_key = key;
+	input_sync(tk->input);
+
+	return IRQ_HANDLED;
+}
+
+static int dir685_tk_probe(struct i2c_client *client)
+{
+	static const u8 bl_data[] = { 0xa7, 0x40 };
+	struct device *dev = &client->dev;
+	struct dir685_touchkeys *tk;
+	int err;
+	int i;
+
+	tk = devm_kzalloc(&client->dev, sizeof(*tk), GFP_KERNEL);
+	if (!tk)
+		return -ENOMEM;
+
+	tk->input = devm_input_allocate_device(dev);
+	if (!tk->input)
+		return -ENOMEM;
+
+	tk->client = client;
+	tk->dev = dev;
+
+	tk->input->keycodesize = sizeof(u16);
+	tk->input->keycodemax = ARRAY_SIZE(tk->codes);
+	tk->input->keycode = tk->codes;
+	tk->codes[0] = KEY_UP;
+	tk->codes[1] = KEY_DOWN;
+	tk->codes[2] = KEY_LEFT;
+	tk->codes[3] = KEY_RIGHT;
+	tk->codes[4] = KEY_ENTER;
+	tk->codes[5] = KEY_WPS_BUTTON;
+	/*
+	 * This key appears in the vendor driver, but I have
+	 * not been able to activate it.
+	 */
+	tk->codes[6] = KEY_RESERVED;
+
+	__set_bit(EV_KEY, tk->input->evbit);
+	for (i = 0; i < ARRAY_SIZE(tk->codes); i++)
+		__set_bit(tk->codes[i], tk->input->keybit);
+	__clear_bit(KEY_RESERVED, tk->input->keybit);
+
+	tk->input->name = "D-Link DIR-685 touchkeys";
+	tk->input->id.bustype = BUS_I2C;
+
+	err = input_register_device(tk->input);
+	if (err)
+		return err;
+
+	/* Set the brightness to max level */
+	err = i2c_master_send(client, bl_data, sizeof(bl_data));
+	if (err != sizeof(bl_data))
+		dev_warn(tk->dev, "error setting brightness level\n");
+
+	if (!client->irq) {
+		dev_err(dev, "no IRQ on the I2C device\n");
+		return -ENODEV;
+	}
+	err = devm_request_threaded_irq(dev, client->irq,
+					NULL, dir685_tk_irq_thread,
+					IRQF_ONESHOT,
+					"dir685-tk", tk);
+	if (err) {
+		dev_err(dev, "can't request IRQ\n");
+		return err;
+	}
+
+	return 0;
+}
+
+static const struct i2c_device_id dir685_tk_id[] = {
+	{ .name = "dir685tk" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, dir685_tk_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id dir685_tk_of_match[] = {
+	{ .compatible = "dlink,dir685-touchkeys" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, dir685_tk_of_match);
+#endif
+
+static struct i2c_driver dir685_tk_i2c_driver = {
+	.driver = {
+		.name	= "dlink-dir685-touchkeys",
+		.of_match_table = of_match_ptr(dir685_tk_of_match),
+	},
+	.probe		= dir685_tk_probe,
+	.id_table	= dir685_tk_id,
+};
+module_i2c_driver(dir685_tk_i2c_driver);
+
+MODULE_AUTHOR("Linus Walleij <linus.walleij@linaro.org>");
+MODULE_DESCRIPTION("D-Link DIR-685 touchkeys driver");
+MODULE_LICENSE("GPL");