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, 321 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-max8998.c b/drivers/rtc/rtc-max8998.c
new file mode 100644
index 000000000..a2c946edc
--- /dev/null
+++ b/drivers/rtc/rtc-max8998.c
@@ -0,0 +1,321 @@
+// SPDX-License-Identifier: GPL-2.0+
+//
+// RTC driver for Maxim MAX8998
+//
+// Copyright (C) 2010 Samsung Electronics Co.Ltd
+// Author: Minkyu Kang <mk7.kang@samsung.com>
+// Author: Joonyoung Shim <jy0922.shim@samsung.com>
+
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/bcd.h>
+#include <linux/irqdomain.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+#include <linux/mfd/max8998.h>
+#include <linux/mfd/max8998-private.h>
+#include <linux/delay.h>
+
+#define MAX8998_RTC_SEC			0x00
+#define MAX8998_RTC_MIN			0x01
+#define MAX8998_RTC_HOUR		0x02
+#define MAX8998_RTC_WEEKDAY		0x03
+#define MAX8998_RTC_DATE		0x04
+#define MAX8998_RTC_MONTH		0x05
+#define MAX8998_RTC_YEAR1		0x06
+#define MAX8998_RTC_YEAR2		0x07
+#define MAX8998_ALARM0_SEC		0x08
+#define MAX8998_ALARM0_MIN		0x09
+#define MAX8998_ALARM0_HOUR		0x0a
+#define MAX8998_ALARM0_WEEKDAY		0x0b
+#define MAX8998_ALARM0_DATE		0x0c
+#define MAX8998_ALARM0_MONTH		0x0d
+#define MAX8998_ALARM0_YEAR1		0x0e
+#define MAX8998_ALARM0_YEAR2		0x0f
+#define MAX8998_ALARM1_SEC		0x10
+#define MAX8998_ALARM1_MIN		0x11
+#define MAX8998_ALARM1_HOUR		0x12
+#define MAX8998_ALARM1_WEEKDAY		0x13
+#define MAX8998_ALARM1_DATE		0x14
+#define MAX8998_ALARM1_MONTH		0x15
+#define MAX8998_ALARM1_YEAR1		0x16
+#define MAX8998_ALARM1_YEAR2		0x17
+#define MAX8998_ALARM0_CONF		0x18
+#define MAX8998_ALARM1_CONF		0x19
+#define MAX8998_RTC_STATUS		0x1a
+#define MAX8998_WTSR_SMPL_CNTL		0x1b
+#define MAX8998_TEST			0x1f
+
+#define HOUR_12				(1 << 7)
+#define HOUR_PM				(1 << 5)
+#define ALARM0_STATUS			(1 << 1)
+#define ALARM1_STATUS			(1 << 2)
+
+enum {
+	RTC_SEC = 0,
+	RTC_MIN,
+	RTC_HOUR,
+	RTC_WEEKDAY,
+	RTC_DATE,
+	RTC_MONTH,
+	RTC_YEAR1,
+	RTC_YEAR2,
+};
+
+struct max8998_rtc_info {
+	struct device		*dev;
+	struct max8998_dev	*max8998;
+	struct i2c_client	*rtc;
+	struct rtc_device	*rtc_dev;
+	int irq;
+	bool lp3974_bug_workaround;
+};
+
+static void max8998_data_to_tm(u8 *data, struct rtc_time *tm)
+{
+	tm->tm_sec = bcd2bin(data[RTC_SEC]);
+	tm->tm_min = bcd2bin(data[RTC_MIN]);
+	if (data[RTC_HOUR] & HOUR_12) {
+		tm->tm_hour = bcd2bin(data[RTC_HOUR] & 0x1f);
+		if (data[RTC_HOUR] & HOUR_PM)
+			tm->tm_hour += 12;
+	} else
+		tm->tm_hour = bcd2bin(data[RTC_HOUR] & 0x3f);
+
+	tm->tm_wday = data[RTC_WEEKDAY] & 0x07;
+	tm->tm_mday = bcd2bin(data[RTC_DATE]);
+	tm->tm_mon = bcd2bin(data[RTC_MONTH]);
+	tm->tm_year = bcd2bin(data[RTC_YEAR1]) + bcd2bin(data[RTC_YEAR2]) * 100;
+	tm->tm_year -= 1900;
+}
+
+static void max8998_tm_to_data(struct rtc_time *tm, u8 *data)
+{
+	data[RTC_SEC] = bin2bcd(tm->tm_sec);
+	data[RTC_MIN] = bin2bcd(tm->tm_min);
+	data[RTC_HOUR] = bin2bcd(tm->tm_hour);
+	data[RTC_WEEKDAY] = tm->tm_wday;
+	data[RTC_DATE] = bin2bcd(tm->tm_mday);
+	data[RTC_MONTH] = bin2bcd(tm->tm_mon);
+	data[RTC_YEAR1] = bin2bcd(tm->tm_year % 100);
+	data[RTC_YEAR2] = bin2bcd((tm->tm_year + 1900) / 100);
+}
+
+static int max8998_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct max8998_rtc_info *info = dev_get_drvdata(dev);
+	u8 data[8];
+	int ret;
+
+	ret = max8998_bulk_read(info->rtc, MAX8998_RTC_SEC, 8, data);
+	if (ret < 0)
+		return ret;
+
+	max8998_data_to_tm(data, tm);
+
+	return 0;
+}
+
+static int max8998_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct max8998_rtc_info *info = dev_get_drvdata(dev);
+	u8 data[8];
+	int ret;
+
+	max8998_tm_to_data(tm, data);
+
+	ret = max8998_bulk_write(info->rtc, MAX8998_RTC_SEC, 8, data);
+
+	if (info->lp3974_bug_workaround)
+		msleep(2000);
+
+	return ret;
+}
+
+static int max8998_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct max8998_rtc_info *info = dev_get_drvdata(dev);
+	u8 data[8];
+	u8 val;
+	int ret;
+
+	ret = max8998_bulk_read(info->rtc, MAX8998_ALARM0_SEC, 8, data);
+	if (ret < 0)
+		return ret;
+
+	max8998_data_to_tm(data, &alrm->time);
+
+	ret = max8998_read_reg(info->rtc, MAX8998_ALARM0_CONF, &val);
+	if (ret < 0)
+		return ret;
+
+	alrm->enabled = !!val;
+
+	ret = max8998_read_reg(info->rtc, MAX8998_RTC_STATUS, &val);
+	if (ret < 0)
+		return ret;
+
+	if (val & ALARM0_STATUS)
+		alrm->pending = 1;
+	else
+		alrm->pending = 0;
+
+	return 0;
+}
+
+static int max8998_rtc_stop_alarm(struct max8998_rtc_info *info)
+{
+	int ret = max8998_write_reg(info->rtc, MAX8998_ALARM0_CONF, 0);
+
+	if (info->lp3974_bug_workaround)
+		msleep(2000);
+
+	return ret;
+}
+
+static int max8998_rtc_start_alarm(struct max8998_rtc_info *info)
+{
+	int ret;
+	u8 alarm0_conf = 0x77;
+
+	/* LP3974 with delay bug chips has rtc alarm bugs with "MONTH" field */
+	if (info->lp3974_bug_workaround)
+		alarm0_conf = 0x57;
+
+	ret = max8998_write_reg(info->rtc, MAX8998_ALARM0_CONF, alarm0_conf);
+
+	if (info->lp3974_bug_workaround)
+		msleep(2000);
+
+	return ret;
+}
+
+static int max8998_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct max8998_rtc_info *info = dev_get_drvdata(dev);
+	u8 data[8];
+	int ret;
+
+	max8998_tm_to_data(&alrm->time, data);
+
+	ret = max8998_rtc_stop_alarm(info);
+	if (ret < 0)
+		return ret;
+
+	ret = max8998_bulk_write(info->rtc, MAX8998_ALARM0_SEC, 8, data);
+	if (ret < 0)
+		return ret;
+
+	if (info->lp3974_bug_workaround)
+		msleep(2000);
+
+	if (alrm->enabled)
+		ret = max8998_rtc_start_alarm(info);
+
+	return ret;
+}
+
+static int max8998_rtc_alarm_irq_enable(struct device *dev,
+					unsigned int enabled)
+{
+	struct max8998_rtc_info *info = dev_get_drvdata(dev);
+
+	if (enabled)
+		return max8998_rtc_start_alarm(info);
+	else
+		return max8998_rtc_stop_alarm(info);
+}
+
+static irqreturn_t max8998_rtc_alarm_irq(int irq, void *data)
+{
+	struct max8998_rtc_info *info = data;
+
+	rtc_update_irq(info->rtc_dev, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops max8998_rtc_ops = {
+	.read_time = max8998_rtc_read_time,
+	.set_time = max8998_rtc_set_time,
+	.read_alarm = max8998_rtc_read_alarm,
+	.set_alarm = max8998_rtc_set_alarm,
+	.alarm_irq_enable = max8998_rtc_alarm_irq_enable,
+};
+
+static int max8998_rtc_probe(struct platform_device *pdev)
+{
+	struct max8998_dev *max8998 = dev_get_drvdata(pdev->dev.parent);
+	struct max8998_platform_data *pdata = max8998->pdata;
+	struct max8998_rtc_info *info;
+	int ret;
+
+	info = devm_kzalloc(&pdev->dev, sizeof(struct max8998_rtc_info),
+			GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	info->dev = &pdev->dev;
+	info->max8998 = max8998;
+	info->rtc = max8998->rtc;
+
+	platform_set_drvdata(pdev, info);
+
+	info->rtc_dev = devm_rtc_device_register(&pdev->dev, "max8998-rtc",
+			&max8998_rtc_ops, THIS_MODULE);
+
+	if (IS_ERR(info->rtc_dev)) {
+		ret = PTR_ERR(info->rtc_dev);
+		dev_err(&pdev->dev, "Failed to register RTC device: %d\n", ret);
+		return ret;
+	}
+
+	if (!max8998->irq_domain)
+		goto no_irq;
+
+	info->irq = irq_create_mapping(max8998->irq_domain, MAX8998_IRQ_ALARM0);
+	if (!info->irq) {
+		dev_warn(&pdev->dev, "Failed to map alarm IRQ\n");
+		goto no_irq;
+	}
+
+	ret = devm_request_threaded_irq(&pdev->dev, info->irq, NULL,
+				max8998_rtc_alarm_irq, 0, "rtc-alarm0", info);
+
+	if (ret < 0)
+		dev_err(&pdev->dev, "Failed to request alarm IRQ: %d: %d\n",
+			info->irq, ret);
+
+no_irq:
+	dev_info(&pdev->dev, "RTC CHIP NAME: %s\n", pdev->id_entry->name);
+	if (pdata && pdata->rtc_delay) {
+		info->lp3974_bug_workaround = true;
+		dev_warn(&pdev->dev, "LP3974 with RTC REGERR option."
+				" RTC updates will be extremely slow.\n");
+	}
+
+	return 0;
+}
+
+static const struct platform_device_id max8998_rtc_id[] = {
+	{ .name = "max8998-rtc", .driver_data = TYPE_MAX8998 },
+	{ .name = "lp3974-rtc", .driver_data = TYPE_LP3974 },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, max8998_rtc_id);
+
+static struct platform_driver max8998_rtc_driver = {
+	.driver		= {
+		.name	= "max8998-rtc",
+	},
+	.probe		= max8998_rtc_probe,
+	.id_table	= max8998_rtc_id,
+};
+
+module_platform_driver(max8998_rtc_driver);
+
+MODULE_AUTHOR("Minkyu Kang <mk7.kang@samsung.com>");
+MODULE_AUTHOR("Joonyoung Shim <jy0922.shim@samsung.com>");
+MODULE_DESCRIPTION("Maxim MAX8998 RTC driver");
+MODULE_LICENSE("GPL");