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, 103 insertions, 0 deletions

diff --git a/drivers/input/misc/ad714x-spi.c b/drivers/input/misc/ad714x-spi.c
new file mode 100644
index 000000000..eb13b4cd6
--- /dev/null
+++ b/drivers/input/misc/ad714x-spi.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * AD714X CapTouch Programmable Controller driver (SPI bus)
+ *
+ * Copyright 2009-2011 Analog Devices Inc.
+ */
+
+#include <linux/input.h>	/* BUS_SPI */
+#include <linux/module.h>
+#include <linux/spi/spi.h>
+#include <linux/pm.h>
+#include <linux/types.h>
+#include "ad714x.h"
+
+#define AD714x_SPI_CMD_PREFIX      0xE000   /* bits 15:11 */
+#define AD714x_SPI_READ            BIT(10)
+
+static int ad714x_spi_read(struct ad714x_chip *chip,
+			   unsigned short reg, unsigned short *data, size_t len)
+{
+	struct spi_device *spi = to_spi_device(chip->dev);
+	struct spi_message message;
+	struct spi_transfer xfer[2];
+	int i;
+	int error;
+
+	spi_message_init(&message);
+	memset(xfer, 0, sizeof(xfer));
+
+	chip->xfer_buf[0] = cpu_to_be16(AD714x_SPI_CMD_PREFIX |
+					AD714x_SPI_READ | reg);
+	xfer[0].tx_buf = &chip->xfer_buf[0];
+	xfer[0].len = sizeof(chip->xfer_buf[0]);
+	spi_message_add_tail(&xfer[0], &message);
+
+	xfer[1].rx_buf = &chip->xfer_buf[1];
+	xfer[1].len = sizeof(chip->xfer_buf[1]) * len;
+	spi_message_add_tail(&xfer[1], &message);
+
+	error = spi_sync(spi, &message);
+	if (unlikely(error)) {
+		dev_err(chip->dev, "SPI read error: %d\n", error);
+		return error;
+	}
+
+	for (i = 0; i < len; i++)
+		data[i] = be16_to_cpu(chip->xfer_buf[i + 1]);
+
+	return 0;
+}
+
+static int ad714x_spi_write(struct ad714x_chip *chip,
+			    unsigned short reg, unsigned short data)
+{
+	struct spi_device *spi = to_spi_device(chip->dev);
+	int error;
+
+	chip->xfer_buf[0] = cpu_to_be16(AD714x_SPI_CMD_PREFIX | reg);
+	chip->xfer_buf[1] = cpu_to_be16(data);
+
+	error = spi_write(spi, (u8 *)chip->xfer_buf,
+			  2 * sizeof(*chip->xfer_buf));
+	if (unlikely(error)) {
+		dev_err(chip->dev, "SPI write error: %d\n", error);
+		return error;
+	}
+
+	return 0;
+}
+
+static int ad714x_spi_probe(struct spi_device *spi)
+{
+	struct ad714x_chip *chip;
+	int err;
+
+	spi->bits_per_word = 8;
+	err = spi_setup(spi);
+	if (err < 0)
+		return err;
+
+	chip = ad714x_probe(&spi->dev, BUS_SPI, spi->irq,
+			    ad714x_spi_read, ad714x_spi_write);
+	if (IS_ERR(chip))
+		return PTR_ERR(chip);
+
+	spi_set_drvdata(spi, chip);
+
+	return 0;
+}
+
+static struct spi_driver ad714x_spi_driver = {
+	.driver = {
+		.name	= "ad714x_captouch",
+		.pm	= pm_sleep_ptr(&ad714x_pm),
+	},
+	.probe		= ad714x_spi_probe,
+};
+
+module_spi_driver(ad714x_spi_driver);
+
+MODULE_DESCRIPTION("Analog Devices AD714X Capacitance Touch Sensor SPI Bus Driver");
+MODULE_AUTHOR("Barry Song <21cnbao@gmail.com>");
+MODULE_LICENSE("GPL");