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, 222 insertions, 0 deletions

diff --git a/drivers/input/touchscreen/ts4800-ts.c b/drivers/input/touchscreen/ts4800-ts.c
new file mode 100644
index 000000000..98422d1e8
--- /dev/null
+++ b/drivers/input/touchscreen/ts4800-ts.c
@@ -0,0 +1,222 @@
+/*
+ * Touchscreen driver for the TS-4800 board
+ *
+ * Copyright (c) 2015 - Savoir-faire Linux
+ *
+ * This file is licensed under the terms of the GNU General Public
+ * License version 2. This program is licensed "as is" without any
+ * warranty of any kind, whether express or implied.
+ */
+
+#include <linux/bitops.h>
+#include <linux/input.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+/* polling interval in ms */
+#define POLL_INTERVAL		3
+
+#define DEBOUNCE_COUNT		1
+
+/* sensor values are 12-bit wide */
+#define MAX_12BIT		((1 << 12) - 1)
+
+#define PENDOWN_MASK		0x1
+
+#define X_OFFSET		0x0
+#define Y_OFFSET		0x2
+
+struct ts4800_ts {
+	struct input_dev        *input;
+	struct device           *dev;
+	char                    phys[32];
+
+	void __iomem            *base;
+	struct regmap           *regmap;
+	unsigned int            reg;
+	unsigned int            bit;
+
+	bool                    pendown;
+	int                     debounce;
+};
+
+static int ts4800_ts_open(struct input_dev *input_dev)
+{
+	struct ts4800_ts *ts = input_get_drvdata(input_dev);
+	int error;
+
+	ts->pendown = false;
+	ts->debounce = DEBOUNCE_COUNT;
+
+	error = regmap_update_bits(ts->regmap, ts->reg, ts->bit, ts->bit);
+	if (error) {
+		dev_warn(ts->dev, "Failed to enable touchscreen: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+static void ts4800_ts_close(struct input_dev *input_dev)
+{
+	struct ts4800_ts *ts = input_get_drvdata(input_dev);
+	int ret;
+
+	ret = regmap_update_bits(ts->regmap, ts->reg, ts->bit, 0);
+	if (ret)
+		dev_warn(ts->dev, "Failed to disable touchscreen\n");
+
+}
+
+static void ts4800_ts_poll(struct input_dev *input_dev)
+{
+	struct ts4800_ts *ts = input_get_drvdata(input_dev);
+	u16 last_x = readw(ts->base + X_OFFSET);
+	u16 last_y = readw(ts->base + Y_OFFSET);
+	bool pendown = last_x & PENDOWN_MASK;
+
+	if (pendown) {
+		if (ts->debounce) {
+			ts->debounce--;
+			return;
+		}
+
+		if (!ts->pendown) {
+			input_report_key(input_dev, BTN_TOUCH, 1);
+			ts->pendown = true;
+		}
+
+		last_x = ((~last_x) >> 4) & MAX_12BIT;
+		last_y = ((~last_y) >> 4) & MAX_12BIT;
+
+		input_report_abs(input_dev, ABS_X, last_x);
+		input_report_abs(input_dev, ABS_Y, last_y);
+		input_sync(input_dev);
+	} else if (ts->pendown) {
+		ts->pendown = false;
+		ts->debounce = DEBOUNCE_COUNT;
+		input_report_key(input_dev, BTN_TOUCH, 0);
+		input_sync(input_dev);
+	}
+}
+
+static int ts4800_parse_dt(struct platform_device *pdev,
+			   struct ts4800_ts *ts)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	u32 reg, bit;
+	int error;
+
+	struct device_node *syscon_np __free(device_node) =
+		of_parse_phandle(np, "syscon", 0);
+	if (!syscon_np) {
+		dev_err(dev, "no syscon property\n");
+		return -ENODEV;
+	}
+
+	ts->regmap = syscon_node_to_regmap(syscon_np);
+	if (IS_ERR(ts->regmap)) {
+		dev_err(dev, "cannot get parent's regmap\n");
+		return PTR_ERR(ts->regmap);
+	}
+
+	error = of_property_read_u32_index(np, "syscon", 1, &reg);
+	if (error < 0) {
+		dev_err(dev, "no offset in syscon\n");
+		return error;
+	}
+
+	ts->reg = reg;
+
+	error = of_property_read_u32_index(np, "syscon", 2, &bit);
+	if (error < 0) {
+		dev_err(dev, "no bit in syscon\n");
+		return error;
+	}
+
+	ts->bit = BIT(bit);
+
+	return 0;
+}
+
+static int ts4800_ts_probe(struct platform_device *pdev)
+{
+	struct input_dev *input_dev;
+	struct ts4800_ts *ts;
+	int error;
+
+	ts = devm_kzalloc(&pdev->dev, sizeof(*ts), GFP_KERNEL);
+	if (!ts)
+		return -ENOMEM;
+
+	error = ts4800_parse_dt(pdev, ts);
+	if (error)
+		return error;
+
+	ts->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(ts->base))
+		return PTR_ERR(ts->base);
+
+	input_dev = devm_input_allocate_device(&pdev->dev);
+	if (!input_dev)
+		return -ENOMEM;
+
+	snprintf(ts->phys, sizeof(ts->phys), "%s/input0", dev_name(&pdev->dev));
+	ts->input = input_dev;
+	ts->dev = &pdev->dev;
+
+	input_set_drvdata(input_dev, ts);
+
+	input_dev->name = "TS-4800 Touchscreen";
+	input_dev->phys = ts->phys;
+
+	input_dev->open = ts4800_ts_open;
+	input_dev->close = ts4800_ts_close;
+
+	input_set_capability(input_dev, EV_KEY, BTN_TOUCH);
+	input_set_abs_params(input_dev, ABS_X, 0, MAX_12BIT, 0, 0);
+	input_set_abs_params(input_dev, ABS_Y, 0, MAX_12BIT, 0, 0);
+
+	error = input_setup_polling(input_dev, ts4800_ts_poll);
+	if (error) {
+		dev_err(&pdev->dev, "Unable to set up polling: %d\n", error);
+		return error;
+	}
+
+	input_set_poll_interval(input_dev, POLL_INTERVAL);
+
+	error = input_register_device(input_dev);
+	if (error) {
+		dev_err(&pdev->dev,
+			"Unable to register input device: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+static const struct of_device_id ts4800_ts_of_match[] = {
+	{ .compatible = "technologic,ts4800-ts", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, ts4800_ts_of_match);
+
+static struct platform_driver ts4800_ts_driver = {
+	.driver = {
+		.name = "ts4800-ts",
+		.of_match_table = ts4800_ts_of_match,
+	},
+	.probe = ts4800_ts_probe,
+};
+module_platform_driver(ts4800_ts_driver);
+
+MODULE_AUTHOR("Damien Riegel <damien.riegel@savoirfairelinux.com>");
+MODULE_DESCRIPTION("TS-4800 Touchscreen Driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:ts4800_ts");