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-max8925.c b/drivers/rtc/rtc-max8925.c
new file mode 100644
index 000000000..6ce8afbea
--- /dev/null
+++ b/drivers/rtc/rtc-max8925.c
@@ -0,0 +1,322 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * RTC driver for Maxim MAX8925
+ *
+ * Copyright (C) 2009-2010 Marvell International Ltd.
+ *	Haojian Zhuang <haojian.zhuang@marvell.com>
+ */
+
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/max8925.h>
+
+enum {
+	RTC_SEC = 0,
+	RTC_MIN,
+	RTC_HOUR,
+	RTC_WEEKDAY,
+	RTC_DATE,
+	RTC_MONTH,
+	RTC_YEAR1,
+	RTC_YEAR2,
+};
+
+#define MAX8925_RTC_SEC			0x00
+#define MAX8925_RTC_MIN			0x01
+#define MAX8925_RTC_HOUR		0x02
+#define MAX8925_RTC_WEEKDAY		0x03
+#define MAX8925_RTC_DATE		0x04
+#define MAX8925_RTC_MONTH		0x05
+#define MAX8925_RTC_YEAR1		0x06
+#define MAX8925_RTC_YEAR2		0x07
+#define MAX8925_ALARM0_SEC		0x08
+#define MAX8925_ALARM0_MIN		0x09
+#define MAX8925_ALARM0_HOUR		0x0a
+#define MAX8925_ALARM0_WEEKDAY		0x0b
+#define MAX8925_ALARM0_DATE		0x0c
+#define MAX8925_ALARM0_MON		0x0d
+#define MAX8925_ALARM0_YEAR1		0x0e
+#define MAX8925_ALARM0_YEAR2		0x0f
+#define MAX8925_ALARM1_SEC		0x10
+#define MAX8925_ALARM1_MIN		0x11
+#define MAX8925_ALARM1_HOUR		0x12
+#define MAX8925_ALARM1_WEEKDAY		0x13
+#define MAX8925_ALARM1_DATE		0x14
+#define MAX8925_ALARM1_MON		0x15
+#define MAX8925_ALARM1_YEAR1		0x16
+#define MAX8925_ALARM1_YEAR2		0x17
+#define MAX8925_RTC_CNTL		0x1b
+#define MAX8925_RTC_STATUS		0x20
+
+#define TIME_NUM			8
+#define ALARM_1SEC			(1 << 7)
+#define HOUR_12				(1 << 7)
+#define HOUR_AM_PM			(1 << 5)
+#define ALARM0_IRQ			(1 << 3)
+#define ALARM1_IRQ			(1 << 2)
+#define ALARM0_STATUS			(1 << 2)
+#define ALARM1_STATUS			(1 << 1)
+
+
+struct max8925_rtc_info {
+	struct rtc_device	*rtc_dev;
+	struct max8925_chip	*chip;
+	struct i2c_client	*rtc;
+	struct device		*dev;
+	int			irq;
+};
+
+static irqreturn_t rtc_update_handler(int irq, void *data)
+{
+	struct max8925_rtc_info *info = (struct max8925_rtc_info *)data;
+
+	/* disable ALARM0 except for 1SEC alarm */
+	max8925_set_bits(info->rtc, MAX8925_ALARM0_CNTL, 0x7f, 0);
+	rtc_update_irq(info->rtc_dev, 1, RTC_IRQF | RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static int tm_calc(struct rtc_time *tm, unsigned char *buf, int len)
+{
+	if (len < TIME_NUM)
+		return -EINVAL;
+	tm->tm_year = (buf[RTC_YEAR2] >> 4) * 1000
+			+ (buf[RTC_YEAR2] & 0xf) * 100
+			+ (buf[RTC_YEAR1] >> 4) * 10
+			+ (buf[RTC_YEAR1] & 0xf);
+	tm->tm_year -= 1900;
+	tm->tm_mon = ((buf[RTC_MONTH] >> 4) & 0x01) * 10
+			+ (buf[RTC_MONTH] & 0x0f);
+	tm->tm_mday = ((buf[RTC_DATE] >> 4) & 0x03) * 10
+			+ (buf[RTC_DATE] & 0x0f);
+	tm->tm_wday = buf[RTC_WEEKDAY] & 0x07;
+	if (buf[RTC_HOUR] & HOUR_12) {
+		tm->tm_hour = ((buf[RTC_HOUR] >> 4) & 0x1) * 10
+				+ (buf[RTC_HOUR] & 0x0f);
+		if (buf[RTC_HOUR] & HOUR_AM_PM)
+			tm->tm_hour += 12;
+	} else
+		tm->tm_hour = ((buf[RTC_HOUR] >> 4) & 0x03) * 10
+				+ (buf[RTC_HOUR] & 0x0f);
+	tm->tm_min = ((buf[RTC_MIN] >> 4) & 0x7) * 10
+			+ (buf[RTC_MIN] & 0x0f);
+	tm->tm_sec = ((buf[RTC_SEC] >> 4) & 0x7) * 10
+			+ (buf[RTC_SEC] & 0x0f);
+	return 0;
+}
+
+static int data_calc(unsigned char *buf, struct rtc_time *tm, int len)
+{
+	unsigned char high, low;
+
+	if (len < TIME_NUM)
+		return -EINVAL;
+
+	high = (tm->tm_year + 1900) / 1000;
+	low = (tm->tm_year + 1900) / 100;
+	low = low - high * 10;
+	buf[RTC_YEAR2] = (high << 4) + low;
+	high = (tm->tm_year + 1900) / 10;
+	low = tm->tm_year + 1900;
+	low = low - high * 10;
+	high = high - (high / 10) * 10;
+	buf[RTC_YEAR1] = (high << 4) + low;
+	high = tm->tm_mon / 10;
+	low = tm->tm_mon;
+	low = low - high * 10;
+	buf[RTC_MONTH] = (high << 4) + low;
+	high = tm->tm_mday / 10;
+	low = tm->tm_mday;
+	low = low - high * 10;
+	buf[RTC_DATE] = (high << 4) + low;
+	buf[RTC_WEEKDAY] = tm->tm_wday;
+	high = tm->tm_hour / 10;
+	low = tm->tm_hour;
+	low = low - high * 10;
+	buf[RTC_HOUR] = (high << 4) + low;
+	high = tm->tm_min / 10;
+	low = tm->tm_min;
+	low = low - high * 10;
+	buf[RTC_MIN] = (high << 4) + low;
+	high = tm->tm_sec / 10;
+	low = tm->tm_sec;
+	low = low - high * 10;
+	buf[RTC_SEC] = (high << 4) + low;
+	return 0;
+}
+
+static int max8925_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct max8925_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[TIME_NUM];
+	int ret;
+
+	ret = max8925_bulk_read(info->rtc, MAX8925_RTC_SEC, TIME_NUM, buf);
+	if (ret < 0)
+		goto out;
+	ret = tm_calc(tm, buf, TIME_NUM);
+out:
+	return ret;
+}
+
+static int max8925_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct max8925_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[TIME_NUM];
+	int ret;
+
+	ret = data_calc(buf, tm, TIME_NUM);
+	if (ret < 0)
+		goto out;
+	ret = max8925_bulk_write(info->rtc, MAX8925_RTC_SEC, TIME_NUM, buf);
+out:
+	return ret;
+}
+
+static int max8925_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct max8925_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[TIME_NUM];
+	int ret;
+
+	ret = max8925_bulk_read(info->rtc, MAX8925_ALARM0_SEC, TIME_NUM, buf);
+	if (ret < 0)
+		goto out;
+	ret = tm_calc(&alrm->time, buf, TIME_NUM);
+	if (ret < 0)
+		goto out;
+	ret = max8925_reg_read(info->rtc, MAX8925_RTC_IRQ_MASK);
+	if (ret < 0)
+		goto out;
+	if (ret & ALARM0_IRQ) {
+		alrm->enabled = 0;
+	} else {
+		ret = max8925_reg_read(info->rtc, MAX8925_ALARM0_CNTL);
+		if (ret < 0)
+			goto out;
+		if (!ret)
+			alrm->enabled = 0;
+		else
+			alrm->enabled = 1;
+	}
+	ret = max8925_reg_read(info->rtc, MAX8925_RTC_STATUS);
+	if (ret < 0)
+		goto out;
+	if (ret & ALARM0_STATUS)
+		alrm->pending = 1;
+	else
+		alrm->pending = 0;
+	return 0;
+out:
+	return ret;
+}
+
+static int max8925_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct max8925_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[TIME_NUM];
+	int ret;
+
+	ret = data_calc(buf, &alrm->time, TIME_NUM);
+	if (ret < 0)
+		goto out;
+	ret = max8925_bulk_write(info->rtc, MAX8925_ALARM0_SEC, TIME_NUM, buf);
+	if (ret < 0)
+		goto out;
+	if (alrm->enabled)
+		/* only enable alarm on year/month/day/hour/min/sec */
+		ret = max8925_reg_write(info->rtc, MAX8925_ALARM0_CNTL, 0x77);
+	else
+		ret = max8925_reg_write(info->rtc, MAX8925_ALARM0_CNTL, 0x0);
+out:
+	return ret;
+}
+
+static const struct rtc_class_ops max8925_rtc_ops = {
+	.read_time	= max8925_rtc_read_time,
+	.set_time	= max8925_rtc_set_time,
+	.read_alarm	= max8925_rtc_read_alarm,
+	.set_alarm	= max8925_rtc_set_alarm,
+};
+
+static int max8925_rtc_probe(struct platform_device *pdev)
+{
+	struct max8925_chip *chip = dev_get_drvdata(pdev->dev.parent);
+	struct max8925_rtc_info *info;
+	int ret;
+
+	info = devm_kzalloc(&pdev->dev, sizeof(struct max8925_rtc_info),
+			    GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+	info->chip = chip;
+	info->rtc = chip->rtc;
+	info->dev = &pdev->dev;
+	info->irq = platform_get_irq(pdev, 0);
+
+	ret = devm_request_threaded_irq(&pdev->dev, info->irq, NULL,
+					rtc_update_handler, IRQF_ONESHOT,
+					"rtc-alarm0", info);
+	if (ret < 0) {
+		dev_err(chip->dev, "Failed to request IRQ: #%d: %d\n",
+			info->irq, ret);
+		return ret;
+	}
+
+	dev_set_drvdata(&pdev->dev, info);
+	/* XXX - isn't this redundant? */
+	platform_set_drvdata(pdev, info);
+
+	device_init_wakeup(&pdev->dev, true);
+
+	info->rtc_dev = devm_rtc_device_register(&pdev->dev, "max8925-rtc",
+					&max8925_rtc_ops, THIS_MODULE);
+	ret = PTR_ERR(info->rtc_dev);
+	if (IS_ERR(info->rtc_dev)) {
+		dev_err(&pdev->dev, "Failed to register RTC device: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int max8925_rtc_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct max8925_chip *chip = dev_get_drvdata(pdev->dev.parent);
+
+	if (device_may_wakeup(dev))
+		chip->wakeup_flag |= 1 << MAX8925_IRQ_RTC_ALARM0;
+	return 0;
+}
+static int max8925_rtc_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct max8925_chip *chip = dev_get_drvdata(pdev->dev.parent);
+
+	if (device_may_wakeup(dev))
+		chip->wakeup_flag &= ~(1 << MAX8925_IRQ_RTC_ALARM0);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(max8925_rtc_pm_ops, max8925_rtc_suspend, max8925_rtc_resume);
+
+static struct platform_driver max8925_rtc_driver = {
+	.driver		= {
+		.name	= "max8925-rtc",
+		.pm     = &max8925_rtc_pm_ops,
+	},
+	.probe		= max8925_rtc_probe,
+};
+
+module_platform_driver(max8925_rtc_driver);
+
+MODULE_DESCRIPTION("Maxim MAX8925 RTC driver");
+MODULE_AUTHOR("Haojian Zhuang <haojian.zhuang@marvell.com>");
+MODULE_LICENSE("GPL");
+