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/touchscreen/ipaq-micro-ts.c b/drivers/input/touchscreen/ipaq-micro-ts.c
new file mode 100644
index 000000000..243e6465d
--- /dev/null
+++ b/drivers/input/touchscreen/ipaq-micro-ts.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * h3600 atmel micro companion support, touchscreen subdevice
+ * Author : Alessandro Gardich <gremlin@gremlin.it>
+ * Author : Dmitry Artamonow <mad_soft@inbox.ru>
+ * Author : Linus Walleij <linus.walleij@linaro.org>
+ */
+
+#include <asm/byteorder.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/pm.h>
+#include <linux/delay.h>
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/mfd/ipaq-micro.h>
+
+struct touchscreen_data {
+	struct input_dev *input;
+	struct ipaq_micro *micro;
+};
+
+static void micro_ts_receive(void *data, int len, unsigned char *msg)
+{
+	struct touchscreen_data *ts = data;
+
+	if (len == 4) {
+		input_report_abs(ts->input, ABS_X,
+				 be16_to_cpup((__be16 *) &msg[2]));
+		input_report_abs(ts->input, ABS_Y,
+				 be16_to_cpup((__be16 *) &msg[0]));
+		input_report_key(ts->input, BTN_TOUCH, 1);
+		input_sync(ts->input);
+	} else if (len == 0) {
+		input_report_abs(ts->input, ABS_X, 0);
+		input_report_abs(ts->input, ABS_Y, 0);
+		input_report_key(ts->input, BTN_TOUCH, 0);
+		input_sync(ts->input);
+	}
+}
+
+static void micro_ts_toggle_receive(struct touchscreen_data *ts, bool enable)
+{
+	struct ipaq_micro *micro = ts->micro;
+
+	guard(spinlock_irq)(&micro->lock);
+
+	if (enable) {
+		micro->ts = micro_ts_receive;
+		micro->ts_data = ts;
+	} else {
+		micro->ts = NULL;
+		micro->ts_data = NULL;
+	}
+}
+
+static int micro_ts_open(struct input_dev *input)
+{
+	struct touchscreen_data *ts = input_get_drvdata(input);
+
+	micro_ts_toggle_receive(ts, true);
+
+	return 0;
+}
+
+static void micro_ts_close(struct input_dev *input)
+{
+	struct touchscreen_data *ts = input_get_drvdata(input);
+
+	micro_ts_toggle_receive(ts, false);
+}
+
+static int micro_ts_probe(struct platform_device *pdev)
+{
+	struct ipaq_micro *micro = dev_get_drvdata(pdev->dev.parent);
+	struct touchscreen_data *ts;
+	int error;
+
+	ts = devm_kzalloc(&pdev->dev, sizeof(*ts), GFP_KERNEL);
+	if (!ts)
+		return -ENOMEM;
+
+	ts->micro = micro;
+
+	ts->input = devm_input_allocate_device(&pdev->dev);
+	if (!ts->input) {
+		dev_err(&pdev->dev, "failed to allocate input device\n");
+		return -ENOMEM;
+	}
+
+	ts->input->name = "ipaq micro ts";
+	ts->input->open = micro_ts_open;
+	ts->input->close = micro_ts_close;
+
+	input_set_drvdata(ts->input, ts);
+
+	input_set_capability(ts->input, EV_KEY, BTN_TOUCH);
+	input_set_capability(ts->input, EV_ABS, ABS_X);
+	input_set_capability(ts->input, EV_ABS, ABS_Y);
+	input_set_abs_params(ts->input, ABS_X, 0, 1023, 0, 0);
+	input_set_abs_params(ts->input, ABS_Y, 0, 1023, 0, 0);
+
+	error = input_register_device(ts->input);
+	if (error) {
+		dev_err(&pdev->dev, "error registering touch input\n");
+		return error;
+	}
+
+	platform_set_drvdata(pdev, ts);
+
+	dev_info(&pdev->dev, "iPAQ micro touchscreen\n");
+
+	return 0;
+}
+
+static int micro_ts_suspend(struct device *dev)
+{
+	struct touchscreen_data *ts = dev_get_drvdata(dev);
+
+	micro_ts_toggle_receive(ts, false);
+
+	return 0;
+}
+
+static int micro_ts_resume(struct device *dev)
+{
+	struct touchscreen_data *ts = dev_get_drvdata(dev);
+	struct input_dev *input = ts->input;
+
+	guard(mutex)(&input->mutex);
+
+	if (input_device_enabled(input))
+		micro_ts_toggle_receive(ts, true);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(micro_ts_dev_pm_ops,
+				micro_ts_suspend, micro_ts_resume);
+
+static struct platform_driver micro_ts_device_driver = {
+	.driver	= {
+		.name	= "ipaq-micro-ts",
+		.pm	= pm_sleep_ptr(&micro_ts_dev_pm_ops),
+	},
+	.probe	= micro_ts_probe,
+};
+module_platform_driver(micro_ts_device_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("driver for iPAQ Atmel micro touchscreen");
+MODULE_ALIAS("platform:ipaq-micro-ts");