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, 177 insertions, 0 deletions

diff --git a/drivers/hid/hid-axff.c b/drivers/hid/hid-axff.c
new file mode 100644
index 000000000..2f4644708
--- /dev/null
+++ b/drivers/hid/hid-axff.c
@@ -0,0 +1,177 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Force feedback support for ACRUX game controllers
+ *
+ * From what I have gathered, these devices are mass produced in China
+ * by several vendors. They often share the same design as the original
+ * Xbox 360 controller.
+ *
+ * 1a34:0802 "ACRUX USB GAMEPAD 8116"
+ *  - tested with an EXEQ EQ-PCU-02090 game controller.
+ *
+ * Copyright (c) 2010 Sergei Kolzun <x0r@dv-life.ru>
+ */
+
+/*
+ */
+
+#include <linux/input.h>
+#include <linux/slab.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+#ifdef CONFIG_HID_ACRUX_FF
+
+struct axff_device {
+	struct hid_report *report;
+};
+
+static int axff_play(struct input_dev *dev, void *data, struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct axff_device *axff = data;
+	struct hid_report *report = axff->report;
+	int field_count = 0;
+	int left, right;
+	int i, j;
+
+	left = effect->u.rumble.strong_magnitude;
+	right = effect->u.rumble.weak_magnitude;
+
+	dbg_hid("called with 0x%04x 0x%04x", left, right);
+
+	left = left * 0xff / 0xffff;
+	right = right * 0xff / 0xffff;
+
+	for (i = 0; i < report->maxfield; i++) {
+		for (j = 0; j < report->field[i]->report_count; j++) {
+			report->field[i]->value[j] =
+				field_count % 2 ? right : left;
+			field_count++;
+		}
+	}
+
+	dbg_hid("running with 0x%02x 0x%02x", left, right);
+	hid_hw_request(hid, axff->report, HID_REQ_SET_REPORT);
+
+	return 0;
+}
+
+static int ax_input_configured(struct hid_device *hid, struct hid_input *hidinput)
+{
+	struct axff_device *axff;
+	struct hid_report *report;
+	struct list_head *report_list = &hid->report_enum[HID_OUTPUT_REPORT].report_list;
+	struct input_dev *dev = hidinput->input;
+	int field_count = 0;
+	int i, j;
+	int error;
+
+	if (!list_is_first(&hidinput->list, &hid->inputs))
+		return 0;
+
+	report = list_first_entry_or_null(report_list, struct hid_report, list);
+	if (!report) {
+		hid_err(hid, "no output reports found\n");
+		return -ENODEV;
+	}
+	for (i = 0; i < report->maxfield; i++) {
+		for (j = 0; j < report->field[i]->report_count; j++) {
+			report->field[i]->value[j] = 0x00;
+			field_count++;
+		}
+	}
+
+	if (field_count < 4 && hid->product != 0xf705) {
+		hid_err(hid, "not enough fields in the report: %d\n",
+			field_count);
+		return -ENODEV;
+	}
+
+	axff = kzalloc_obj(struct axff_device);
+	if (!axff)
+		return -ENOMEM;
+
+	axff->report = report;
+	set_bit(FF_RUMBLE, dev->ffbit);
+
+	error = input_ff_create_memless(dev, axff, axff_play);
+	if (error)
+		goto err_free_mem;
+
+	hid_hw_request(hid, axff->report, HID_REQ_SET_REPORT);
+
+	hid_info(hid, "Force Feedback for ACRUX game controllers by Sergei Kolzun <x0r@dv-life.ru>\n");
+
+	return 0;
+
+err_free_mem:
+	kfree(axff);
+	return error;
+}
+#else
+static inline int ax_input_configured(struct hid_device *hid,
+				      struct hid_input *hidinput)
+{
+	return 0;
+}
+#endif
+
+static int ax_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int error;
+
+	dev_dbg(&hdev->dev, "ACRUX HID hardware probe...\n");
+
+	error = hid_parse(hdev);
+	if (error) {
+		hid_err(hdev, "parse failed\n");
+		return error;
+	}
+
+	error = hid_hw_start(hdev, HID_CONNECT_DEFAULT);
+	if (error) {
+		hid_err(hdev, "hw start failed\n");
+		return error;
+	}
+	/*
+	 * We need to start polling device right away, otherwise
+	 * it will go into a coma.
+	 */
+	error = hid_hw_open(hdev);
+	if (error) {
+		dev_err(&hdev->dev, "hw open failed\n");
+		hid_hw_stop(hdev);
+		return error;
+	}
+
+	return 0;
+}
+
+static void ax_remove(struct hid_device *hdev)
+{
+	hid_hw_close(hdev);
+	hid_hw_stop(hdev);
+}
+
+static const struct hid_device_id ax_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ACRUX, 0x0802), },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ACRUX, 0xf705), },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, ax_devices);
+
+static struct hid_driver ax_driver = {
+	.name		= "acrux",
+	.id_table	= ax_devices,
+	.probe		= ax_probe,
+	.remove		= ax_remove,
+	.input_configured = ax_input_configured,
+};
+module_hid_driver(ax_driver);
+
+MODULE_AUTHOR("Sergei Kolzun");
+MODULE_DESCRIPTION("Force feedback support for ACRUX game controllers");
+MODULE_LICENSE("GPL");