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, 74 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/ad7879-i2c.c b/drivers/input/touchscreen/ad7879-i2c.c
new file mode 100644
index 000000000..c1ccdf86b
--- /dev/null
+++ b/drivers/input/touchscreen/ad7879-i2c.c
@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * AD7879-1/AD7889-1 touchscreen (I2C bus)
+ *
+ * Copyright (C) 2008-2010 Michael Hennerich, Analog Devices Inc.
+ */
+
+#include <linux/input.h>	/* BUS_I2C */
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/of.h>
+#include <linux/pm.h>
+#include <linux/regmap.h>
+
+#include "ad7879.h"
+
+#define AD7879_DEVID		0x79	/* AD7879-1/AD7889-1 */
+
+static const struct regmap_config ad7879_i2c_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 16,
+	.max_register = 15,
+};
+
+static int ad7879_i2c_probe(struct i2c_client *client)
+{
+	struct regmap *regmap;
+
+	if (!i2c_check_functionality(client->adapter,
+				     I2C_FUNC_SMBUS_WORD_DATA)) {
+		dev_err(&client->dev, "SMBUS Word Data not Supported\n");
+		return -EIO;
+	}
+
+	regmap = devm_regmap_init_i2c(client, &ad7879_i2c_regmap_config);
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
+
+	return ad7879_probe(&client->dev, regmap, client->irq,
+			    BUS_I2C, AD7879_DEVID);
+}
+
+static const struct i2c_device_id ad7879_id[] = {
+	{ .name = "ad7879" },
+	{ .name = "ad7889" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ad7879_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id ad7879_i2c_dt_ids[] = {
+	{ .compatible = "adi,ad7879-1", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ad7879_i2c_dt_ids);
+#endif
+
+static struct i2c_driver ad7879_i2c_driver = {
+	.driver = {
+		.name		= "ad7879",
+		.dev_groups	= ad7879_groups,
+		.pm		= &ad7879_pm_ops,
+		.of_match_table	= of_match_ptr(ad7879_i2c_dt_ids),
+	},
+	.probe		= ad7879_i2c_probe,
+	.id_table	= ad7879_id,
+};
+
+module_i2c_driver(ad7879_i2c_driver);
+
+MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
+MODULE_DESCRIPTION("AD7879(-1) touchscreen I2C bus driver");
+MODULE_LICENSE("GPL");