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, 322 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-rx8581.c b/drivers/rtc/rtc-rx8581.c
new file mode 100644
index 000000000..cf4dab94c
--- /dev/null
+++ b/drivers/rtc/rtc-rx8581.c
@@ -0,0 +1,322 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * An I2C driver for the Epson RX8581 RTC
+ *
+ * Author: Martyn Welch <martyn.welch@ge.com>
+ * Copyright 2008 GE Intelligent Platforms Embedded Systems, Inc.
+ *
+ * Based on: rtc-pcf8563.c (An I2C driver for the Philips PCF8563 RTC)
+ * Copyright 2005-06 Tower Technologies
+ */
+
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/bcd.h>
+#include <linux/of.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+#include <linux/log2.h>
+
+#define RX8581_REG_SC		0x00 /* Second in BCD */
+#define RX8581_REG_MN		0x01 /* Minute in BCD */
+#define RX8581_REG_HR		0x02 /* Hour in BCD */
+#define RX8581_REG_DW		0x03 /* Day of Week */
+#define RX8581_REG_DM		0x04 /* Day of Month in BCD */
+#define RX8581_REG_MO		0x05 /* Month in BCD */
+#define RX8581_REG_YR		0x06 /* Year in BCD */
+#define RX8581_REG_RAM		0x07 /* RAM */
+#define RX8581_REG_AMN		0x08 /* Alarm Min in BCD*/
+#define RX8581_REG_AHR		0x09 /* Alarm Hour in BCD */
+#define RX8581_REG_ADM		0x0A
+#define RX8581_REG_ADW		0x0A
+#define RX8581_REG_TMR0		0x0B
+#define RX8581_REG_TMR1		0x0C
+#define RX8581_REG_EXT		0x0D /* Extension Register */
+#define RX8581_REG_FLAG		0x0E /* Flag Register */
+#define RX8581_REG_CTRL		0x0F /* Control Register */
+
+
+/* Flag Register bit definitions */
+#define RX8581_FLAG_UF		0x20 /* Update */
+#define RX8581_FLAG_TF		0x10 /* Timer */
+#define RX8581_FLAG_AF		0x08 /* Alarm */
+#define RX8581_FLAG_VLF		0x02 /* Voltage Low */
+
+/* Control Register bit definitions */
+#define RX8581_CTRL_UIE		0x20 /* Update Interrupt Enable */
+#define RX8581_CTRL_TIE		0x10 /* Timer Interrupt Enable */
+#define RX8581_CTRL_AIE		0x08 /* Alarm Interrupt Enable */
+#define RX8581_CTRL_STOP	0x02 /* STOP bit */
+#define RX8581_CTRL_RESET	0x01 /* RESET bit */
+
+#define RX8571_USER_RAM		0x10
+#define RX8571_NVRAM_SIZE	0x10
+
+struct rx85x1_config {
+	struct regmap_config regmap;
+	unsigned int num_nvram;
+};
+
+/*
+ * In the routines that deal directly with the rx8581 hardware, we use
+ * rtc_time -- month 0-11, hour 0-23, yr = calendar year-epoch.
+ */
+static int rx8581_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	unsigned char date[7];
+	unsigned int data;
+	int err;
+	struct regmap *regmap = i2c_get_clientdata(client);
+
+	/* First we ensure that the "update flag" is not set, we read the
+	 * time and date then re-read the "update flag". If the update flag
+	 * has been set, we know that the time has changed during the read so
+	 * we repeat the whole process again.
+	 */
+	err = regmap_read(regmap, RX8581_REG_FLAG, &data);
+	if (err < 0)
+		return err;
+
+	if (data & RX8581_FLAG_VLF) {
+		dev_warn(dev,
+			 "low voltage detected, date/time is not reliable.\n");
+		return -EINVAL;
+	}
+
+	do {
+		/* If update flag set, clear it */
+		if (data & RX8581_FLAG_UF) {
+			err = regmap_write(regmap, RX8581_REG_FLAG,
+					   data & ~RX8581_FLAG_UF);
+			if (err < 0)
+				return err;
+		}
+
+		/* Now read time and date */
+		err = regmap_bulk_read(regmap, RX8581_REG_SC, date,
+				       sizeof(date));
+		if (err < 0)
+			return err;
+
+		/* Check flag register */
+		err = regmap_read(regmap, RX8581_REG_FLAG, &data);
+		if (err < 0)
+			return err;
+	} while (data & RX8581_FLAG_UF);
+
+	dev_dbg(dev, "%s: raw data is sec=%02x, min=%02x, hr=%02x, "
+		"wday=%02x, mday=%02x, mon=%02x, year=%02x\n",
+		__func__,
+		date[0], date[1], date[2], date[3], date[4], date[5], date[6]);
+
+	tm->tm_sec = bcd2bin(date[RX8581_REG_SC] & 0x7F);
+	tm->tm_min = bcd2bin(date[RX8581_REG_MN] & 0x7F);
+	tm->tm_hour = bcd2bin(date[RX8581_REG_HR] & 0x3F); /* rtc hr 0-23 */
+	tm->tm_wday = ilog2(date[RX8581_REG_DW] & 0x7F);
+	tm->tm_mday = bcd2bin(date[RX8581_REG_DM] & 0x3F);
+	tm->tm_mon = bcd2bin(date[RX8581_REG_MO] & 0x1F) - 1; /* rtc mn 1-12 */
+	tm->tm_year = bcd2bin(date[RX8581_REG_YR]) + 100;
+
+	dev_dbg(dev, "%s: tm is secs=%d, mins=%d, hours=%d, "
+		"mday=%d, mon=%d, year=%d, wday=%d\n",
+		__func__,
+		tm->tm_sec, tm->tm_min, tm->tm_hour,
+		tm->tm_mday, tm->tm_mon, tm->tm_year, tm->tm_wday);
+
+	return 0;
+}
+
+static int rx8581_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int err;
+	unsigned char buf[7];
+	struct regmap *regmap = i2c_get_clientdata(client);
+
+	dev_dbg(dev, "%s: secs=%d, mins=%d, hours=%d, "
+		"mday=%d, mon=%d, year=%d, wday=%d\n",
+		__func__,
+		tm->tm_sec, tm->tm_min, tm->tm_hour,
+		tm->tm_mday, tm->tm_mon, tm->tm_year, tm->tm_wday);
+
+	/* hours, minutes and seconds */
+	buf[RX8581_REG_SC] = bin2bcd(tm->tm_sec);
+	buf[RX8581_REG_MN] = bin2bcd(tm->tm_min);
+	buf[RX8581_REG_HR] = bin2bcd(tm->tm_hour);
+
+	buf[RX8581_REG_DM] = bin2bcd(tm->tm_mday);
+
+	/* month, 1 - 12 */
+	buf[RX8581_REG_MO] = bin2bcd(tm->tm_mon + 1);
+
+	/* year and century */
+	buf[RX8581_REG_YR] = bin2bcd(tm->tm_year - 100);
+	buf[RX8581_REG_DW] = (0x1 << tm->tm_wday);
+
+	/* Stop the clock */
+	err = regmap_update_bits(regmap, RX8581_REG_CTRL,
+				 RX8581_CTRL_STOP, RX8581_CTRL_STOP);
+	if (err < 0)
+		return err;
+
+	/* write register's data */
+	err = regmap_bulk_write(regmap, RX8581_REG_SC, buf, sizeof(buf));
+	if (err < 0)
+		return err;
+
+	/* get VLF and clear it */
+	err = regmap_update_bits(regmap, RX8581_REG_FLAG, RX8581_FLAG_VLF, 0);
+	if (err < 0)
+		return err;
+
+	/* Restart the clock */
+	return regmap_update_bits(regmap, RX8581_REG_CTRL,
+				 RX8581_CTRL_STOP, 0);
+}
+
+static const struct rtc_class_ops rx8581_rtc_ops = {
+	.read_time	= rx8581_rtc_read_time,
+	.set_time	= rx8581_rtc_set_time,
+};
+
+static int rx8571_nvram_read(void *priv, unsigned int offset, void *val,
+			     size_t bytes)
+{
+	struct regmap *regmap = priv;
+
+	return regmap_bulk_read(regmap, RX8571_USER_RAM + offset, val, bytes);
+}
+
+static int rx8571_nvram_write(void *priv, unsigned int offset, void *val,
+			      size_t bytes)
+{
+	struct regmap *regmap = priv;
+
+	return regmap_bulk_write(regmap, RX8571_USER_RAM + offset, val, bytes);
+}
+
+static int rx85x1_nvram_read(void *priv, unsigned int offset, void *val,
+			     size_t bytes)
+{
+	struct regmap *regmap = priv;
+	unsigned int tmp_val;
+	int ret;
+
+	ret = regmap_read(regmap, RX8581_REG_RAM, &tmp_val);
+	(*(unsigned char *)val) = (unsigned char) tmp_val;
+
+	return ret;
+}
+
+static int rx85x1_nvram_write(void *priv, unsigned int offset, void *val,
+			      size_t bytes)
+{
+	struct regmap *regmap = priv;
+	unsigned char tmp_val;
+
+	tmp_val = *((unsigned char *)val);
+	return regmap_write(regmap, RX8581_REG_RAM, (unsigned int)tmp_val);
+}
+
+static const struct rx85x1_config rx8581_config = {
+	.regmap = {
+		.reg_bits = 8,
+		.val_bits = 8,
+		.max_register = 0xf,
+	},
+	.num_nvram = 1
+};
+
+static const struct rx85x1_config rx8571_config = {
+	.regmap = {
+		.reg_bits = 8,
+		.val_bits = 8,
+		.max_register = 0x1f,
+	},
+	.num_nvram = 2
+};
+
+static int rx8581_probe(struct i2c_client *client)
+{
+	struct regmap *regmap;
+	const struct rx85x1_config *config = &rx8581_config;
+	const void *data = of_device_get_match_data(&client->dev);
+	struct rtc_device *rtc;
+	static struct nvmem_config nvmem_cfg[] = {
+		{
+			.name = "rx85x1-",
+			.word_size = 1,
+			.stride = 1,
+			.size = 1,
+			.reg_read = rx85x1_nvram_read,
+			.reg_write = rx85x1_nvram_write,
+		}, {
+			.name = "rx8571-",
+			.word_size = 1,
+			.stride = 1,
+			.size = RX8571_NVRAM_SIZE,
+			.reg_read = rx8571_nvram_read,
+			.reg_write = rx8571_nvram_write,
+		},
+	};
+	int ret, i;
+
+	dev_dbg(&client->dev, "%s\n", __func__);
+
+	if (data)
+		config = data;
+
+	regmap = devm_regmap_init_i2c(client, &config->regmap);
+	if (IS_ERR(regmap))
+		return PTR_ERR(regmap);
+
+	i2c_set_clientdata(client, regmap);
+
+	rtc = devm_rtc_allocate_device(&client->dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	rtc->ops = &rx8581_rtc_ops;
+	rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	rtc->range_max = RTC_TIMESTAMP_END_2099;
+	rtc->start_secs = 0;
+	rtc->set_start_time = true;
+
+	ret = devm_rtc_register_device(rtc);
+
+	for (i = 0; i < config->num_nvram; i++) {
+		nvmem_cfg[i].priv = regmap;
+		devm_rtc_nvmem_register(rtc, &nvmem_cfg[i]);
+	}
+
+	return ret;
+}
+
+static const struct i2c_device_id rx8581_id[] = {
+	{ .name = "rx8581" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, rx8581_id);
+
+static const __maybe_unused struct of_device_id rx8581_of_match[] = {
+	{ .compatible = "epson,rx8571", .data = &rx8571_config },
+	{ .compatible = "epson,rx8581", .data = &rx8581_config },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(of, rx8581_of_match);
+
+static struct i2c_driver rx8581_driver = {
+	.driver		= {
+		.name	= "rtc-rx8581",
+		.of_match_table = of_match_ptr(rx8581_of_match),
+	},
+	.probe		= rx8581_probe,
+	.id_table	= rx8581_id,
+};
+
+module_i2c_driver(rx8581_driver);
+
+MODULE_AUTHOR("Martyn Welch <martyn.welch@ge.com>");
+MODULE_DESCRIPTION("Epson RX-8571/RX-8581 RTC driver");
+MODULE_LICENSE("GPL");