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, 119 insertions, 0 deletions

diff --git a/drivers/mfd/rt4831.c b/drivers/mfd/rt4831.c
new file mode 100644
index 000000000..1ab8870e4
--- /dev/null
+++ b/drivers/mfd/rt4831.c
@@ -0,0 +1,119 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (c) 2021 Richtek Technology Corp.
+ *
+ * Author: ChiYuan Huang <cy_huang@richtek.com>
+ */
+
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/mfd/core.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+
+#define RT4831_REG_REVISION	0x01
+#define RT4831_REG_ENABLE	0x08
+#define RT4831_REG_I2CPROT	0x15
+
+#define RICHTEK_VENDOR_ID	0x03
+#define RT4831_VID_MASK		GENMASK(1, 0)
+#define RT4831_RESET_MASK	BIT(7)
+#define RT4831_I2CSAFETMR_MASK	BIT(0)
+
+static const struct mfd_cell rt4831_subdevs[] = {
+	MFD_CELL_OF("rt4831-backlight", NULL, NULL, 0, 0, "richtek,rt4831-backlight"),
+	MFD_CELL_NAME("rt4831-regulator")
+};
+
+static bool rt4831_is_accessible_reg(struct device *dev, unsigned int reg)
+{
+	if (reg >= RT4831_REG_REVISION && reg <= RT4831_REG_I2CPROT)
+		return true;
+	return false;
+}
+
+static const struct regmap_config rt4831_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = RT4831_REG_I2CPROT,
+
+	.readable_reg = rt4831_is_accessible_reg,
+	.writeable_reg = rt4831_is_accessible_reg,
+};
+
+static int rt4831_probe(struct i2c_client *client)
+{
+	struct gpio_desc *enable_gpio;
+	struct regmap *regmap;
+	unsigned int chip_id;
+	int ret;
+
+	enable_gpio = devm_gpiod_get_optional(&client->dev, "enable", GPIOD_OUT_HIGH);
+	if (IS_ERR(enable_gpio)) {
+		dev_err(&client->dev, "Failed to get 'enable' GPIO\n");
+		return PTR_ERR(enable_gpio);
+	}
+
+	regmap = devm_regmap_init_i2c(client, &rt4831_regmap_config);
+	if (IS_ERR(regmap)) {
+		dev_err(&client->dev, "Failed to initialize regmap\n");
+		return PTR_ERR(regmap);
+	}
+
+	ret = regmap_read(regmap, RT4831_REG_REVISION, &chip_id);
+	if (ret) {
+		dev_err(&client->dev, "Failed to get H/W revision\n");
+		return ret;
+	}
+
+	if ((chip_id & RT4831_VID_MASK) != RICHTEK_VENDOR_ID) {
+		dev_err(&client->dev, "Chip vendor ID 0x%02x not matched\n", chip_id);
+		return -ENODEV;
+	}
+
+	/*
+	 * Used to prevent the abnormal shutdown.
+	 * If SCL/SDA both keep low for one second to reset HW.
+	 */
+	ret = regmap_update_bits(regmap, RT4831_REG_I2CPROT, RT4831_I2CSAFETMR_MASK,
+				 RT4831_I2CSAFETMR_MASK);
+	if (ret) {
+		dev_err(&client->dev, "Failed to enable I2C safety timer\n");
+		return ret;
+	}
+
+	return devm_mfd_add_devices(&client->dev, PLATFORM_DEVID_AUTO, rt4831_subdevs,
+				    ARRAY_SIZE(rt4831_subdevs), NULL, 0, NULL);
+}
+
+static void rt4831_remove(struct i2c_client *client)
+{
+	struct regmap *regmap = dev_get_regmap(&client->dev, NULL);
+	int ret;
+
+	/* Disable WLED and DSV outputs */
+	ret = regmap_update_bits(regmap, RT4831_REG_ENABLE, RT4831_RESET_MASK, RT4831_RESET_MASK);
+	if (ret)
+		dev_warn(&client->dev, "Failed to disable outputs (%pe)\n", ERR_PTR(ret));
+}
+
+static const struct of_device_id __maybe_unused rt4831_of_match[] = {
+	{ .compatible = "richtek,rt4831", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, rt4831_of_match);
+
+static struct i2c_driver rt4831_driver = {
+	.driver = {
+		.name = "rt4831",
+		.of_match_table = rt4831_of_match,
+	},
+	.probe = rt4831_probe,
+	.remove = rt4831_remove,
+};
+module_i2c_driver(rt4831_driver);
+
+MODULE_AUTHOR("ChiYuan Huang <cy_huang@richtek.com>");
+MODULE_DESCRIPTION("Richtek RT4831 core driver");
+MODULE_LICENSE("GPL v2");