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, 135 insertions, 0 deletions

diff --git a/drivers/input/misc/e3x0-button.c b/drivers/input/misc/e3x0-button.c
new file mode 100644
index 000000000..5bd527117
--- /dev/null
+++ b/drivers/input/misc/e3x0-button.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2014, National Instruments Corp. All rights reserved.
+ *
+ * Driver for NI Ettus Research USRP E3x0 Button Driver
+ */
+
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/of.h>
+#include <linux/slab.h>
+
+static irqreturn_t e3x0_button_release_handler(int irq, void *data)
+{
+	struct input_dev *idev = data;
+
+	input_report_key(idev, KEY_POWER, 0);
+	input_sync(idev);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t e3x0_button_press_handler(int irq, void *data)
+{
+	struct input_dev *idev = data;
+
+	input_report_key(idev, KEY_POWER, 1);
+	pm_wakeup_event(idev->dev.parent, 0);
+	input_sync(idev);
+
+	return IRQ_HANDLED;
+}
+
+static int e3x0_button_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(platform_get_irq_byname(pdev, "press"));
+
+	return 0;
+}
+
+static int e3x0_button_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(platform_get_irq_byname(pdev, "press"));
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(e3x0_button_pm_ops,
+				e3x0_button_suspend, e3x0_button_resume);
+
+static int e3x0_button_probe(struct platform_device *pdev)
+{
+	struct input_dev *input;
+	int irq_press, irq_release;
+	int error;
+
+	irq_press = platform_get_irq_byname(pdev, "press");
+	if (irq_press < 0)
+		return irq_press;
+
+	irq_release = platform_get_irq_byname(pdev, "release");
+	if (irq_release < 0)
+		return irq_release;
+
+	input = devm_input_allocate_device(&pdev->dev);
+	if (!input)
+		return -ENOMEM;
+
+	input->name = "NI Ettus Research USRP E3x0 Button Driver";
+	input->phys = "e3x0_button/input0";
+	input->dev.parent = &pdev->dev;
+
+	input_set_capability(input, EV_KEY, KEY_POWER);
+
+	error = devm_request_irq(&pdev->dev, irq_press,
+				 e3x0_button_press_handler, 0,
+				 "e3x0-button", input);
+	if (error) {
+		dev_err(&pdev->dev, "Failed to request 'press' IRQ#%d: %d\n",
+			irq_press, error);
+		return error;
+	}
+
+	error = devm_request_irq(&pdev->dev, irq_release,
+				 e3x0_button_release_handler, 0,
+				 "e3x0-button", input);
+	if (error) {
+		dev_err(&pdev->dev, "Failed to request 'release' IRQ#%d: %d\n",
+			irq_release, error);
+		return error;
+	}
+
+	error = input_register_device(input);
+	if (error) {
+		dev_err(&pdev->dev, "Can't register input device: %d\n", error);
+		return error;
+	}
+
+	device_init_wakeup(&pdev->dev, 1);
+	return 0;
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id e3x0_button_match[] = {
+	{ .compatible = "ettus,e3x0-button", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, e3x0_button_match);
+#endif
+
+static struct platform_driver e3x0_button_driver = {
+	.driver		= {
+		.name	= "e3x0-button",
+		.of_match_table = of_match_ptr(e3x0_button_match),
+		.pm	= pm_sleep_ptr(&e3x0_button_pm_ops),
+	},
+	.probe		= e3x0_button_probe,
+};
+
+module_platform_driver(e3x0_button_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Moritz Fischer <moritz.fischer@ettus.com>");
+MODULE_DESCRIPTION("NI Ettus Research USRP E3x0 Button driver");
+MODULE_ALIAS("platform:e3x0-button");