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, 252 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-as3722.c b/drivers/rtc/rtc-as3722.c
new file mode 100644
index 000000000..9682d6457
--- /dev/null
+++ b/drivers/rtc/rtc-as3722.c
@@ -0,0 +1,252 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * rtc-as3722.c - Real Time Clock driver for ams AS3722 PMICs
+ *
+ * Copyright (C) 2013 ams AG
+ * Copyright (c) 2013, NVIDIA Corporation. All rights reserved.
+ *
+ * Author: Florian Lobmaier <florian.lobmaier@ams.com>
+ * Author: Laxman Dewangan <ldewangan@nvidia.com>
+ */
+
+#include <linux/bcd.h>
+#include <linux/completion.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/ioctl.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mfd/as3722.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/time.h>
+
+#define AS3722_RTC_START_YEAR	  2000
+struct as3722_rtc {
+	struct rtc_device	*rtc;
+	struct device		*dev;
+	struct as3722		*as3722;
+	int			alarm_irq;
+	bool			irq_enable;
+};
+
+static void as3722_time_to_reg(u8 *rbuff, struct rtc_time *tm)
+{
+	rbuff[0] = bin2bcd(tm->tm_sec);
+	rbuff[1] = bin2bcd(tm->tm_min);
+	rbuff[2] = bin2bcd(tm->tm_hour);
+	rbuff[3] = bin2bcd(tm->tm_mday);
+	rbuff[4] = bin2bcd(tm->tm_mon + 1);
+	rbuff[5] = bin2bcd(tm->tm_year - (AS3722_RTC_START_YEAR - 1900));
+}
+
+static void as3722_reg_to_time(u8 *rbuff, struct rtc_time *tm)
+{
+	tm->tm_sec = bcd2bin(rbuff[0] & 0x7F);
+	tm->tm_min = bcd2bin(rbuff[1] & 0x7F);
+	tm->tm_hour = bcd2bin(rbuff[2] & 0x3F);
+	tm->tm_mday = bcd2bin(rbuff[3] & 0x3F);
+	tm->tm_mon = bcd2bin(rbuff[4] & 0x1F) - 1;
+	tm->tm_year = (AS3722_RTC_START_YEAR - 1900) + bcd2bin(rbuff[5] & 0x7F);
+	return;
+}
+
+static int as3722_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	ret = as3722_block_read(as3722, AS3722_RTC_SECOND_REG,
+			6, as_time_array);
+	if (ret < 0) {
+		dev_err(dev, "RTC_SECOND reg block read failed %d\n", ret);
+		return ret;
+	}
+	as3722_reg_to_time(as_time_array, tm);
+	return 0;
+}
+
+static int as3722_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	if (tm->tm_year < (AS3722_RTC_START_YEAR - 1900))
+		return -EINVAL;
+
+	as3722_time_to_reg(as_time_array, tm);
+	ret = as3722_block_write(as3722, AS3722_RTC_SECOND_REG, 6,
+			as_time_array);
+	if (ret < 0)
+		dev_err(dev, "RTC_SECOND reg block write failed %d\n", ret);
+	return ret;
+}
+
+static int as3722_rtc_alarm_irq_enable(struct device *dev,
+		unsigned int enabled)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+
+	if (enabled && !as3722_rtc->irq_enable) {
+		enable_irq(as3722_rtc->alarm_irq);
+		as3722_rtc->irq_enable = true;
+	} else if (!enabled && as3722_rtc->irq_enable)  {
+		disable_irq(as3722_rtc->alarm_irq);
+		as3722_rtc->irq_enable = false;
+	}
+	return 0;
+}
+
+static int as3722_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	ret = as3722_block_read(as3722, AS3722_RTC_ALARM_SECOND_REG, 6,
+			as_time_array);
+	if (ret < 0) {
+		dev_err(dev, "RTC_ALARM_SECOND block read failed %d\n", ret);
+		return ret;
+	}
+
+	as3722_reg_to_time(as_time_array, &alrm->time);
+	return 0;
+}
+
+static int as3722_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	if (alrm->time.tm_year < (AS3722_RTC_START_YEAR - 1900))
+		return -EINVAL;
+
+	ret = as3722_rtc_alarm_irq_enable(dev, 0);
+	if (ret < 0) {
+		dev_err(dev, "Disable RTC alarm failed\n");
+		return ret;
+	}
+
+	as3722_time_to_reg(as_time_array, &alrm->time);
+	ret = as3722_block_write(as3722, AS3722_RTC_ALARM_SECOND_REG, 6,
+			as_time_array);
+	if (ret < 0) {
+		dev_err(dev, "RTC_ALARM_SECOND block write failed %d\n", ret);
+		return ret;
+	}
+
+	if (alrm->enabled)
+		ret = as3722_rtc_alarm_irq_enable(dev, alrm->enabled);
+	return ret;
+}
+
+static irqreturn_t as3722_alarm_irq(int irq, void *data)
+{
+	struct as3722_rtc *as3722_rtc = data;
+
+	rtc_update_irq(as3722_rtc->rtc, 1, RTC_IRQF | RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops as3722_rtc_ops = {
+	.read_time = as3722_rtc_read_time,
+	.set_time = as3722_rtc_set_time,
+	.read_alarm = as3722_rtc_read_alarm,
+	.set_alarm = as3722_rtc_set_alarm,
+	.alarm_irq_enable = as3722_rtc_alarm_irq_enable,
+};
+
+static int as3722_rtc_probe(struct platform_device *pdev)
+{
+	struct as3722 *as3722 = dev_get_drvdata(pdev->dev.parent);
+	struct as3722_rtc *as3722_rtc;
+	int ret;
+
+	as3722_rtc = devm_kzalloc(&pdev->dev, sizeof(*as3722_rtc), GFP_KERNEL);
+	if (!as3722_rtc)
+		return -ENOMEM;
+
+	as3722_rtc->as3722 = as3722;
+	as3722_rtc->dev = &pdev->dev;
+	platform_set_drvdata(pdev, as3722_rtc);
+
+	/* Enable the RTC to make sure it is running. */
+	ret = as3722_update_bits(as3722, AS3722_RTC_CONTROL_REG,
+			AS3722_RTC_ON | AS3722_RTC_ALARM_WAKEUP_EN,
+			AS3722_RTC_ON | AS3722_RTC_ALARM_WAKEUP_EN);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "RTC_CONTROL reg write failed: %d\n", ret);
+		return ret;
+	}
+
+	device_init_wakeup(&pdev->dev, true);
+
+	as3722_rtc->rtc = devm_rtc_device_register(&pdev->dev, "as3722-rtc",
+				&as3722_rtc_ops, THIS_MODULE);
+	if (IS_ERR(as3722_rtc->rtc)) {
+		ret = PTR_ERR(as3722_rtc->rtc);
+		dev_err(&pdev->dev, "RTC register failed: %d\n", ret);
+		return ret;
+	}
+
+	as3722_rtc->alarm_irq = platform_get_irq(pdev, 0);
+	dev_info(&pdev->dev, "RTC interrupt %d\n", as3722_rtc->alarm_irq);
+
+	ret = devm_request_threaded_irq(&pdev->dev, as3722_rtc->alarm_irq, NULL,
+			as3722_alarm_irq, IRQF_ONESHOT,
+			"rtc-alarm", as3722_rtc);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to request alarm IRQ %d: %d\n",
+				as3722_rtc->alarm_irq, ret);
+		return ret;
+	}
+	disable_irq(as3722_rtc->alarm_irq);
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int as3722_rtc_suspend(struct device *dev)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(as3722_rtc->alarm_irq);
+
+	return 0;
+}
+
+static int as3722_rtc_resume(struct device *dev)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(as3722_rtc->alarm_irq);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(as3722_rtc_pm_ops, as3722_rtc_suspend,
+			 as3722_rtc_resume);
+
+static struct platform_driver as3722_rtc_driver = {
+	.probe = as3722_rtc_probe,
+	.driver = {
+		.name = "as3722-rtc",
+		.pm = &as3722_rtc_pm_ops,
+	},
+};
+module_platform_driver(as3722_rtc_driver);
+
+MODULE_DESCRIPTION("RTC driver for AS3722 PMICs");
+MODULE_ALIAS("platform:as3722-rtc");
+MODULE_AUTHOR("Florian Lobmaier <florian.lobmaier@ams.com>");
+MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
+MODULE_LICENSE("GPL");