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, 319 insertions, 0 deletions

diff --git a/drivers/hwmon/max1668.c b/drivers/hwmon/max1668.c
new file mode 100644
index 000000000..32548f564
--- /dev/null
+++ b/drivers/hwmon/max1668.c
@@ -0,0 +1,319 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2011 David George <david.george@ska.ac.za>
+ *
+ * based on adm1021.c
+ * some credit to Christoph Scheurer, but largely a rewrite
+ */
+
+#include <linux/bitops.h>
+#include <linux/bits.h>
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/slab.h>
+
+/* Addresses to scan */
+static const unsigned short max1668_addr_list[] = {
+	0x18, 0x19, 0x1a, 0x29, 0x2a, 0x2b, 0x4c, 0x4d, 0x4e, I2C_CLIENT_END };
+
+/* max1668 registers */
+
+#define MAX1668_REG_TEMP(nr)	(nr)
+#define MAX1668_REG_STAT1	0x05
+#define MAX1668_REG_STAT2	0x06
+#define MAX1668_REG_MAN_ID	0xfe
+#define MAX1668_REG_DEV_ID	0xff
+
+/* limits */
+
+/* high limits */
+#define MAX1668_REG_LIMH(nr)	(0x08 + 2 * (nr))
+/* read low limits */
+#define MAX1668_REG_LIML(nr)	(0x09 + 2 * (nr))
+
+/* manufacturer and device ID Constants */
+#define MAN_ID_MAXIM		0x4d
+#define DEV_ID_MAX1668		0x3
+#define DEV_ID_MAX1805		0x5
+#define DEV_ID_MAX1989		0xb
+
+/* read only mode module parameter */
+static bool read_only;
+module_param(read_only, bool, 0);
+MODULE_PARM_DESC(read_only, "Don't set any values, read only mode");
+
+struct max1668_data {
+	struct regmap *regmap;
+	int channels;
+};
+
+static int max1668_read(struct device *dev, enum hwmon_sensor_types type,
+			u32 attr, int channel, long *val)
+{
+	struct max1668_data *data = dev_get_drvdata(dev);
+	struct regmap *regmap = data->regmap;
+	u32 regs[2] = { MAX1668_REG_STAT1, MAX1668_REG_TEMP(channel) };
+	u8 regvals[2];
+	u32 regval;
+	int ret;
+
+	switch (attr) {
+	case hwmon_temp_input:
+		ret = regmap_read(regmap, MAX1668_REG_TEMP(channel), &regval);
+		if (ret)
+			return ret;
+		*val = sign_extend32(regval, 7) * 1000;
+		break;
+	case hwmon_temp_min:
+		ret = regmap_read(regmap, MAX1668_REG_LIML(channel), &regval);
+		if (ret)
+			return ret;
+		*val = sign_extend32(regval, 7) * 1000;
+		break;
+	case hwmon_temp_max:
+		ret = regmap_read(regmap, MAX1668_REG_LIMH(channel), &regval);
+		if (ret)
+			return ret;
+		*val = sign_extend32(regval, 7) * 1000;
+		break;
+	case hwmon_temp_min_alarm:
+		ret = regmap_read(regmap,
+				  channel ? MAX1668_REG_STAT2 : MAX1668_REG_STAT1,
+				  &regval);
+		if (ret)
+			return ret;
+		if (channel)
+			*val = !!(regval & BIT(9 - channel * 2));
+		else
+			*val = !!(regval & BIT(5));
+		break;
+	case hwmon_temp_max_alarm:
+		ret = regmap_read(regmap,
+				  channel ? MAX1668_REG_STAT2 : MAX1668_REG_STAT1,
+				  &regval);
+		if (ret)
+			return ret;
+		if (channel)
+			*val = !!(regval & BIT(8 - channel * 2));
+		else
+			*val = !!(regval & BIT(6));
+		break;
+	case hwmon_temp_fault:
+		ret = regmap_multi_reg_read(regmap, regs, regvals, 2);
+		if (ret)
+			return ret;
+		*val = !!((regvals[0] & BIT(4)) && regvals[1] == 127);
+		break;
+	default:
+		return -EOPNOTSUPP;
+	}
+	return 0;
+}
+
+static int max1668_write(struct device *dev, enum hwmon_sensor_types type,
+			 u32 attr, int channel, long val)
+{
+	struct max1668_data *data = dev_get_drvdata(dev);
+	struct regmap *regmap = data->regmap;
+
+	val = clamp_val(val / 1000, -128, 127);
+
+	switch (attr) {
+	case hwmon_temp_min:
+		return regmap_write(regmap, MAX1668_REG_LIML(channel), val);
+	case hwmon_temp_max:
+		return regmap_write(regmap, MAX1668_REG_LIMH(channel), val);
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
+static umode_t max1668_is_visible(const void *_data, enum hwmon_sensor_types type,
+				  u32 attr, int channel)
+{
+	const struct max1668_data *data = _data;
+
+	if (channel >= data->channels)
+		return 0;
+
+	switch (attr) {
+	case hwmon_temp_min:
+	case hwmon_temp_max:
+		return read_only ? 0444 : 0644;
+	case hwmon_temp_input:
+	case hwmon_temp_min_alarm:
+	case hwmon_temp_max_alarm:
+		return 0444;
+	case hwmon_temp_fault:
+		if (channel)
+			return 0444;
+		break;
+	default:
+		break;
+	}
+	return 0;
+}
+
+static const struct hwmon_channel_info * const max1668_info[] = {
+	HWMON_CHANNEL_INFO(temp,
+			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX |
+			   HWMON_T_MIN_ALARM | HWMON_T_MAX_ALARM,
+			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX |
+			   HWMON_T_MIN_ALARM | HWMON_T_MAX_ALARM |
+			   HWMON_T_FAULT,
+			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX |
+			   HWMON_T_MIN_ALARM | HWMON_T_MAX_ALARM |
+			   HWMON_T_FAULT,
+			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX |
+			   HWMON_T_MIN_ALARM | HWMON_T_MAX_ALARM |
+			   HWMON_T_FAULT,
+			   HWMON_T_INPUT | HWMON_T_MIN | HWMON_T_MAX |
+			   HWMON_T_MIN_ALARM | HWMON_T_MAX_ALARM |
+			   HWMON_T_FAULT),
+	NULL
+};
+
+static const struct hwmon_ops max1668_hwmon_ops = {
+	.is_visible = max1668_is_visible,
+	.read = max1668_read,
+	.write = max1668_write,
+};
+
+static const struct hwmon_chip_info max1668_chip_info = {
+	.ops = &max1668_hwmon_ops,
+	.info = max1668_info,
+};
+
+/* Return 0 if detection is successful, -ENODEV otherwise */
+static int max1668_detect(struct i2c_client *client,
+			  struct i2c_board_info *info)
+{
+	struct i2c_adapter *adapter = client->adapter;
+	const char *type_name;
+	int man_id, dev_id;
+
+	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA))
+		return -ENODEV;
+
+	/* Check for unsupported part */
+	man_id = i2c_smbus_read_byte_data(client, MAX1668_REG_MAN_ID);
+	if (man_id != MAN_ID_MAXIM)
+		return -ENODEV;
+
+	dev_id = i2c_smbus_read_byte_data(client, MAX1668_REG_DEV_ID);
+	if (dev_id < 0)
+		return -ENODEV;
+
+	type_name = NULL;
+	if (dev_id == DEV_ID_MAX1668)
+		type_name = "max1668";
+	else if (dev_id == DEV_ID_MAX1805)
+		type_name = "max1805";
+	else if (dev_id == DEV_ID_MAX1989)
+		type_name = "max1989";
+
+	if (!type_name)
+		return -ENODEV;
+
+	strscpy(info->type, type_name, I2C_NAME_SIZE);
+
+	return 0;
+}
+
+/* regmap */
+
+static int max1668_reg_read(void *context, unsigned int reg, unsigned int *val)
+{
+	int ret;
+
+	ret = i2c_smbus_read_byte_data(context, reg);
+	if (ret < 0)
+		return ret;
+
+	*val = ret;
+	return 0;
+}
+
+static int max1668_reg_write(void *context, unsigned int reg, unsigned int val)
+{
+	return i2c_smbus_write_byte_data(context, reg + 11, val);
+}
+
+static bool max1668_regmap_is_volatile(struct device *dev, unsigned int reg)
+{
+	return reg <= MAX1668_REG_STAT2;
+}
+
+static bool max1668_regmap_is_writeable(struct device *dev, unsigned int reg)
+{
+	return reg > MAX1668_REG_STAT2 && reg <= MAX1668_REG_LIML(4);
+}
+
+static const struct regmap_config max1668_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.cache_type = REGCACHE_MAPLE,
+	.volatile_reg = max1668_regmap_is_volatile,
+	.writeable_reg = max1668_regmap_is_writeable,
+};
+
+static const struct regmap_bus max1668_regmap_bus = {
+	.reg_write = max1668_reg_write,
+	.reg_read = max1668_reg_read,
+};
+
+static int max1668_probe(struct i2c_client *client)
+{
+	struct i2c_adapter *adapter = client->adapter;
+	struct device *dev = &client->dev;
+	struct device *hwmon_dev;
+	struct max1668_data *data;
+
+	if (!i2c_check_functionality(adapter, I2C_FUNC_SMBUS_BYTE_DATA))
+		return -ENODEV;
+
+	data = devm_kzalloc(dev, sizeof(struct max1668_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->regmap = devm_regmap_init(dev, &max1668_regmap_bus, client,
+					&max1668_regmap_config);
+	if (IS_ERR(data->regmap))
+		return PTR_ERR(data->regmap);
+
+	data->channels = (uintptr_t)i2c_get_match_data(client);
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name, data,
+							 &max1668_chip_info, NULL);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id max1668_id[] = {
+	{ .name = "max1668", .driver_data = 5 },
+	{ .name = "max1805", .driver_data = 3 },
+	{ .name = "max1989", .driver_data = 5 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max1668_id);
+
+/* This is the driver that will be inserted */
+static struct i2c_driver max1668_driver = {
+	.class = I2C_CLASS_HWMON,
+	.driver = {
+		  .name	= "max1668",
+		  },
+	.probe = max1668_probe,
+	.id_table = max1668_id,
+	.detect	= max1668_detect,
+	.address_list = max1668_addr_list,
+};
+
+module_i2c_driver(max1668_driver);
+
+MODULE_AUTHOR("David George <david.george@ska.ac.za>");
+MODULE_DESCRIPTION("MAX1668 remote temperature sensor driver");
+MODULE_LICENSE("GPL");