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, 248 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ssd202d.c b/drivers/rtc/rtc-ssd202d.c
new file mode 100644
index 000000000..72aa02eb8
--- /dev/null
+++ b/drivers/rtc/rtc-ssd202d.c
@@ -0,0 +1,248 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Real time clocks driver for MStar/SigmaStar SSD202D SoCs.
+ *
+ * (C) 2021 Daniel Palmer
+ * (C) 2023 Romain Perier
+ */
+
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/regmap.h>
+#include <linux/pm.h>
+
+#define REG_CTRL	0x0
+#define REG_CTRL1	0x4
+#define REG_ISO_CTRL	0xc
+#define REG_WRDATA_L	0x10
+#define REG_WRDATA_H	0x14
+#define REG_ISOACK	0x20
+#define REG_RDDATA_L	0x24
+#define REG_RDDATA_H	0x28
+#define REG_RDCNT_L	0x30
+#define REG_RDCNT_H	0x34
+#define REG_CNT_TRIG	0x38
+#define REG_PWRCTRL	0x3c
+#define REG_RTC_TEST	0x54
+
+#define CNT_RD_TRIG_BIT BIT(0)
+#define CNT_RD_BIT BIT(0)
+#define BASE_WR_BIT BIT(1)
+#define BASE_RD_BIT BIT(2)
+#define CNT_RST_BIT BIT(3)
+#define ISO_CTRL_ACK_MASK BIT(3)
+#define ISO_CTRL_ACK_SHIFT 3
+#define SW0_WR_BIT BIT(5)
+#define SW1_WR_BIT BIT(6)
+#define SW0_RD_BIT BIT(7)
+#define SW1_RD_BIT BIT(8)
+
+#define ISO_CTRL_MASK GENMASK(2, 0)
+
+struct ssd202d_rtc {
+	struct rtc_device *rtc_dev;
+	void __iomem *base;
+};
+
+static u8 read_iso_en(void __iomem *base)
+{
+	return readb(base + REG_RTC_TEST) & 0x1;
+}
+
+static u8 read_iso_ctrl_ack(void __iomem *base)
+{
+	return (readb(base + REG_ISOACK) & ISO_CTRL_ACK_MASK) >> ISO_CTRL_ACK_SHIFT;
+}
+
+static int ssd202d_rtc_isoctrl(struct ssd202d_rtc *priv)
+{
+	static const unsigned int sequence[] = { 0x0, 0x1, 0x3, 0x7, 0x5, 0x1, 0x0 };
+	unsigned int val;
+	struct device *dev = &priv->rtc_dev->dev;
+	int i, ret;
+
+	/*
+	 * This gates iso_en by writing a special sequence of bytes to iso_ctrl
+	 * and ensuring that it has been correctly applied by reading iso_ctrl_ack
+	 */
+	for (i = 0; i < ARRAY_SIZE(sequence); i++) {
+		writeb(sequence[i] & ISO_CTRL_MASK, priv->base +  REG_ISO_CTRL);
+
+		ret = read_poll_timeout(read_iso_ctrl_ack, val, val == (i % 2), 100,
+					20 * 100, true, priv->base);
+		if (ret) {
+			dev_dbg(dev, "Timeout waiting for ack byte %i (%x) of sequence\n", i,
+				sequence[i]);
+			return ret;
+		}
+	}
+
+	/*
+	 * At this point iso_en should be raised for 1ms
+	 */
+	ret = read_poll_timeout(read_iso_en, val, val, 100, 22 * 100, true, priv->base);
+	if (ret)
+		dev_dbg(dev, "Timeout waiting for iso_en\n");
+	mdelay(2);
+	return 0;
+}
+
+static void ssd202d_rtc_read_reg(struct ssd202d_rtc *priv, unsigned int reg,
+				 unsigned int field, unsigned int *base)
+{
+	unsigned int l, h;
+	u16 val;
+
+	/* Ask for the content of an RTC value into RDDATA by gating iso_en,
+	 * then iso_en is gated and the content of RDDATA can be read
+	 */
+	val = readw(priv->base + reg);
+	writew(val | field, priv->base + reg);
+	ssd202d_rtc_isoctrl(priv);
+	writew(val & ~field, priv->base + reg);
+
+	l = readw(priv->base + REG_RDDATA_L);
+	h = readw(priv->base + REG_RDDATA_H);
+
+	*base = (h << 16) | l;
+}
+
+static void ssd202d_rtc_write_reg(struct ssd202d_rtc *priv, unsigned int reg,
+				  unsigned int field, u32 base)
+{
+	u16 val;
+
+	/* Set the content of an RTC value from WRDATA by gating iso_en */
+	val = readw(priv->base + reg);
+	writew(val | field, priv->base + reg);
+	writew(base, priv->base + REG_WRDATA_L);
+	writew(base >> 16, priv->base + REG_WRDATA_H);
+	ssd202d_rtc_isoctrl(priv);
+	writew(val & ~field, priv->base + reg);
+}
+
+static int ssd202d_rtc_read_counter(struct ssd202d_rtc *priv, unsigned int *counter)
+{
+	unsigned int l, h;
+	u16 val;
+
+	val = readw(priv->base + REG_CTRL1);
+	writew(val | CNT_RD_BIT, priv->base + REG_CTRL1);
+	ssd202d_rtc_isoctrl(priv);
+	writew(val & ~CNT_RD_BIT, priv->base + REG_CTRL1);
+
+	val = readw(priv->base + REG_CTRL1);
+	writew(val | CNT_RD_TRIG_BIT, priv->base + REG_CNT_TRIG);
+	writew(val & ~CNT_RD_TRIG_BIT, priv->base + REG_CNT_TRIG);
+
+	l = readw(priv->base + REG_RDCNT_L);
+	h = readw(priv->base + REG_RDCNT_H);
+
+	*counter = (h << 16) | l;
+
+	return 0;
+}
+
+static int ssd202d_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ssd202d_rtc *priv = dev_get_drvdata(dev);
+	unsigned int sw0, base, counter;
+	u32 seconds;
+	int ret;
+
+	/* Check that RTC is enabled by SW */
+	ssd202d_rtc_read_reg(priv, REG_CTRL, SW0_RD_BIT, &sw0);
+	if (sw0 != 1)
+		return -EINVAL;
+
+	/* Get RTC base value from RDDATA */
+	ssd202d_rtc_read_reg(priv, REG_CTRL, BASE_RD_BIT, &base);
+	/* Get RTC counter value from RDDATA */
+	ret = ssd202d_rtc_read_counter(priv, &counter);
+	if (ret)
+		return ret;
+
+	seconds = base + counter;
+
+	rtc_time64_to_tm(seconds, tm);
+
+	return 0;
+}
+
+static int ssd202d_rtc_reset_counter(struct ssd202d_rtc *priv)
+{
+	u16 val;
+
+	val = readw(priv->base + REG_CTRL);
+	writew(val | CNT_RST_BIT, priv->base + REG_CTRL);
+	ssd202d_rtc_isoctrl(priv);
+	writew(val & ~CNT_RST_BIT, priv->base + REG_CTRL);
+	ssd202d_rtc_isoctrl(priv);
+
+	return 0;
+}
+
+static int ssd202d_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ssd202d_rtc *priv = dev_get_drvdata(dev);
+	unsigned long seconds = rtc_tm_to_time64(tm);
+
+	ssd202d_rtc_write_reg(priv, REG_CTRL, BASE_WR_BIT, seconds);
+	ssd202d_rtc_reset_counter(priv);
+	ssd202d_rtc_write_reg(priv, REG_CTRL, SW0_WR_BIT, 1);
+
+	return 0;
+}
+
+static const struct rtc_class_ops ssd202d_rtc_ops = {
+	.read_time = ssd202d_rtc_read_time,
+	.set_time = ssd202d_rtc_set_time,
+};
+
+static int ssd202d_rtc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct ssd202d_rtc *priv;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(struct ssd202d_rtc), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	priv->rtc_dev = devm_rtc_allocate_device(dev);
+	if (IS_ERR(priv->rtc_dev))
+		return PTR_ERR(priv->rtc_dev);
+
+	priv->rtc_dev->ops = &ssd202d_rtc_ops;
+	priv->rtc_dev->range_max = U32_MAX;
+
+	platform_set_drvdata(pdev, priv);
+
+	return devm_rtc_register_device(priv->rtc_dev);
+}
+
+static const struct of_device_id ssd202d_rtc_of_match_table[] = {
+	{ .compatible = "mstar,ssd202d-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ssd202d_rtc_of_match_table);
+
+static struct platform_driver ssd202d_rtc_driver = {
+	.probe = ssd202d_rtc_probe,
+	.driver = {
+		.name = "ssd202d-rtc",
+		.of_match_table = ssd202d_rtc_of_match_table,
+	},
+};
+module_platform_driver(ssd202d_rtc_driver);
+
+MODULE_AUTHOR("Daniel Palmer <daniel@thingy.jp>");
+MODULE_AUTHOR("Romain Perier <romain.perier@gmail.com>");
+MODULE_DESCRIPTION("MStar SSD202D RTC Driver");
+MODULE_LICENSE("GPL");