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, 163 insertions, 0 deletions

diff --git a/drivers/usb/misc/usb4604.c b/drivers/usb/misc/usb4604.c
new file mode 100644
index 000000000..2ae965671
--- /dev/null
+++ b/drivers/usb/misc/usb4604.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Driver for SMSC USB4604 USB HSIC 4-port 2.0 hub controller driver
+ * Based on usb3503 driver
+ *
+ * Copyright (c) 2012-2013 Dongjin Kim (tobetter@gmail.com)
+ * Copyright (c) 2016 Linaro Ltd.
+ */
+
+#include <linux/i2c.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/gpio/consumer.h>
+
+enum usb4604_mode {
+	USB4604_MODE_UNKNOWN,
+	USB4604_MODE_HUB,
+	USB4604_MODE_STANDBY,
+};
+
+struct usb4604 {
+	enum usb4604_mode	mode;
+	struct device		*dev;
+	struct gpio_desc	*gpio_reset;
+};
+
+static void usb4604_reset(struct usb4604 *hub, int state)
+{
+	gpiod_set_value_cansleep(hub->gpio_reset, state);
+
+	/* Wait for i2c logic to come up */
+	if (state)
+		msleep(250);
+}
+
+static int usb4604_connect(struct usb4604 *hub)
+{
+	struct device *dev = hub->dev;
+	struct i2c_client *client = to_i2c_client(dev);
+	int err;
+	u8 connect_cmd[] = { 0xaa, 0x55, 0x00 };
+
+	usb4604_reset(hub, 1);
+
+	err = i2c_master_send(client, connect_cmd, ARRAY_SIZE(connect_cmd));
+	if (err < 0) {
+		usb4604_reset(hub, 0);
+		return err;
+	}
+
+	hub->mode = USB4604_MODE_HUB;
+	dev_dbg(dev, "switched to HUB mode\n");
+
+	return 0;
+}
+
+static int usb4604_switch_mode(struct usb4604 *hub, enum usb4604_mode mode)
+{
+	struct device *dev = hub->dev;
+	int err = 0;
+
+	switch (mode) {
+	case USB4604_MODE_HUB:
+		err = usb4604_connect(hub);
+		break;
+
+	case USB4604_MODE_STANDBY:
+		usb4604_reset(hub, 0);
+		dev_dbg(dev, "switched to STANDBY mode\n");
+		break;
+
+	default:
+		dev_err(dev, "unknown mode is requested\n");
+		err = -EINVAL;
+		break;
+	}
+
+	return err;
+}
+
+static int usb4604_probe(struct usb4604 *hub)
+{
+	struct device *dev = hub->dev;
+	struct device_node *np = dev->of_node;
+	struct gpio_desc *gpio;
+	u32 mode = USB4604_MODE_HUB;
+
+	gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW);
+	if (IS_ERR(gpio))
+		return PTR_ERR(gpio);
+	hub->gpio_reset = gpio;
+
+	if (of_property_read_u32(np, "initial-mode", &hub->mode))
+		hub->mode = mode;
+
+	return usb4604_switch_mode(hub, hub->mode);
+}
+
+static int usb4604_i2c_probe(struct i2c_client *i2c)
+{
+	struct usb4604 *hub;
+
+	hub = devm_kzalloc(&i2c->dev, sizeof(*hub), GFP_KERNEL);
+	if (!hub)
+		return -ENOMEM;
+
+	i2c_set_clientdata(i2c, hub);
+	hub->dev = &i2c->dev;
+
+	return usb4604_probe(hub);
+}
+
+static int __maybe_unused usb4604_i2c_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct usb4604 *hub = i2c_get_clientdata(client);
+
+	usb4604_switch_mode(hub, USB4604_MODE_STANDBY);
+
+	return 0;
+}
+
+static int __maybe_unused usb4604_i2c_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct usb4604 *hub = i2c_get_clientdata(client);
+
+	usb4604_switch_mode(hub, hub->mode);
+
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(usb4604_i2c_pm_ops, usb4604_i2c_suspend,
+		usb4604_i2c_resume);
+
+static const struct i2c_device_id usb4604_id[] = {
+	{ .name = "usb4604" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, usb4604_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id usb4604_of_match[] = {
+	{ .compatible = "smsc,usb4604" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, usb4604_of_match);
+#endif
+
+static struct i2c_driver usb4604_i2c_driver = {
+	.driver = {
+		.name = "usb4604",
+		.pm = pm_ptr(&usb4604_i2c_pm_ops),
+		.of_match_table = of_match_ptr(usb4604_of_match),
+	},
+	.probe		= usb4604_i2c_probe,
+	.id_table	= usb4604_id,
+};
+module_i2c_driver(usb4604_i2c_driver);
+
+MODULE_DESCRIPTION("USB4604 USB HUB driver");
+MODULE_LICENSE("GPL v2");