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, 174 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1216.c b/drivers/rtc/rtc-ds1216.c
new file mode 100644
index 000000000..7eeb3f359
--- /dev/null
+++ b/drivers/rtc/rtc-ds1216.c
@@ -0,0 +1,174 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Dallas DS1216 RTC driver
+ *
+ * Copyright (c) 2007 Thomas Bogendoerfer
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+#include <linux/bcd.h>
+#include <linux/slab.h>
+
+struct ds1216_regs {
+	u8 tsec;
+	u8 sec;
+	u8 min;
+	u8 hour;
+	u8 wday;
+	u8 mday;
+	u8 month;
+	u8 year;
+};
+
+#define DS1216_HOUR_1224	(1 << 7)
+#define DS1216_HOUR_AMPM	(1 << 5)
+
+struct ds1216_priv {
+	struct rtc_device *rtc;
+	void __iomem *ioaddr;
+};
+
+static const u8 magic[] = {
+	0xc5, 0x3a, 0xa3, 0x5c, 0xc5, 0x3a, 0xa3, 0x5c
+};
+
+/*
+ * Read the 64 bit we'd like to have - It a series
+ * of 64 bits showing up in the LSB of the base register.
+ *
+ */
+static void ds1216_read(u8 __iomem *ioaddr, u8 *buf)
+{
+	unsigned char c;
+	int i, j;
+
+	for (i = 0; i < 8; i++) {
+		c = 0;
+		for (j = 0; j < 8; j++)
+			c |= (readb(ioaddr) & 0x1) << j;
+		buf[i] = c;
+	}
+}
+
+static void ds1216_write(u8 __iomem *ioaddr, const u8 *buf)
+{
+	unsigned char c;
+	int i, j;
+
+	for (i = 0; i < 8; i++) {
+		c = buf[i];
+		for (j = 0; j < 8; j++) {
+			writeb(c, ioaddr);
+			c = c >> 1;
+		}
+	}
+}
+
+static void ds1216_switch_ds_to_clock(u8 __iomem *ioaddr)
+{
+	/* Reset magic pointer */
+	readb(ioaddr);
+	/* Write 64 bit magic to DS1216 */
+	ds1216_write(ioaddr, magic);
+}
+
+static int ds1216_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ds1216_priv *priv = dev_get_drvdata(dev);
+	struct ds1216_regs regs;
+
+	ds1216_switch_ds_to_clock(priv->ioaddr);
+	ds1216_read(priv->ioaddr, (u8 *)&regs);
+
+	tm->tm_sec = bcd2bin(regs.sec);
+	tm->tm_min = bcd2bin(regs.min);
+	if (regs.hour & DS1216_HOUR_1224) {
+		/* AM/PM mode */
+		tm->tm_hour = bcd2bin(regs.hour & 0x1f);
+		if (regs.hour & DS1216_HOUR_AMPM)
+			tm->tm_hour += 12;
+	} else
+		tm->tm_hour = bcd2bin(regs.hour & 0x3f);
+	tm->tm_wday = (regs.wday & 7) - 1;
+	tm->tm_mday = bcd2bin(regs.mday & 0x3f);
+	tm->tm_mon = bcd2bin(regs.month & 0x1f);
+	tm->tm_year = bcd2bin(regs.year);
+	if (tm->tm_year < 70)
+		tm->tm_year += 100;
+
+	return 0;
+}
+
+static int ds1216_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ds1216_priv *priv = dev_get_drvdata(dev);
+	struct ds1216_regs regs;
+
+	ds1216_switch_ds_to_clock(priv->ioaddr);
+	ds1216_read(priv->ioaddr, (u8 *)&regs);
+
+	regs.tsec = 0; /* clear 0.1 and 0.01 seconds */
+	regs.sec = bin2bcd(tm->tm_sec);
+	regs.min = bin2bcd(tm->tm_min);
+	regs.hour &= DS1216_HOUR_1224;
+	if (regs.hour && tm->tm_hour > 12) {
+		regs.hour |= DS1216_HOUR_AMPM;
+		tm->tm_hour -= 12;
+	}
+	regs.hour |= bin2bcd(tm->tm_hour);
+	regs.wday &= ~7;
+	regs.wday |= tm->tm_wday;
+	regs.mday = bin2bcd(tm->tm_mday);
+	regs.month = bin2bcd(tm->tm_mon);
+	regs.year = bin2bcd(tm->tm_year % 100);
+
+	ds1216_switch_ds_to_clock(priv->ioaddr);
+	ds1216_write(priv->ioaddr, (u8 *)&regs);
+	return 0;
+}
+
+static const struct rtc_class_ops ds1216_rtc_ops = {
+	.read_time	= ds1216_rtc_read_time,
+	.set_time	= ds1216_rtc_set_time,
+};
+
+static int __init ds1216_rtc_probe(struct platform_device *pdev)
+{
+	struct ds1216_priv *priv;
+	u8 dummy[8];
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, priv);
+
+	priv->ioaddr = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->ioaddr))
+		return PTR_ERR(priv->ioaddr);
+
+	priv->rtc = devm_rtc_device_register(&pdev->dev, "ds1216",
+					&ds1216_rtc_ops, THIS_MODULE);
+	if (IS_ERR(priv->rtc))
+		return PTR_ERR(priv->rtc);
+
+	/* dummy read to get clock into a known state */
+	ds1216_read(priv->ioaddr, dummy);
+	return 0;
+}
+
+static struct platform_driver ds1216_rtc_platform_driver = {
+	.driver		= {
+		.name	= "rtc-ds1216",
+	},
+};
+
+module_platform_driver_probe(ds1216_rtc_platform_driver, ds1216_rtc_probe);
+
+MODULE_AUTHOR("Thomas Bogendoerfer <tsbogend@alpha.franken.de>");
+MODULE_DESCRIPTION("DS1216 RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:rtc-ds1216");