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, 167 insertions, 0 deletions

diff --git a/drivers/hid/hid-a4tech.c b/drivers/hid/hid-a4tech.c
new file mode 100644
index 000000000..54bfaf611
--- /dev/null
+++ b/drivers/hid/hid-a4tech.c
@@ -0,0 +1,167 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  HID driver for some a4tech "special" devices
+ *
+ *  Copyright (c) 1999 Andreas Gal
+ *  Copyright (c) 2000-2005 Vojtech Pavlik <vojtech@suse.cz>
+ *  Copyright (c) 2005 Michael Haboustak <mike-@cinci.rr.com> for Concept2, Inc
+ *  Copyright (c) 2006-2007 Jiri Kosina
+ *  Copyright (c) 2008 Jiri Slaby
+ */
+
+/*
+ */
+
+#include <linux/device.h>
+#include <linux/input.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+
+#include "hid-ids.h"
+
+#define A4_2WHEEL_MOUSE_HACK_7	0x01
+#define A4_2WHEEL_MOUSE_HACK_B8	0x02
+
+#define A4_WHEEL_ORIENTATION	(HID_UP_GENDESK | 0x000000b8)
+
+struct a4tech_sc {
+	unsigned long quirks;
+	unsigned int hw_wheel;
+	__s32 delayed_value;
+};
+
+static int a4_input_mapping(struct hid_device *hdev, struct hid_input *hi,
+			    struct hid_field *field, struct hid_usage *usage,
+			    unsigned long **bit, int *max)
+{
+	struct a4tech_sc *a4 = hid_get_drvdata(hdev);
+
+	if (a4->quirks & A4_2WHEEL_MOUSE_HACK_B8 &&
+	    usage->hid == A4_WHEEL_ORIENTATION) {
+		/*
+		 * We do not want to have this usage mapped to anything as it's
+		 * nonstandard and doesn't really behave like an HID report.
+		 * It's only selecting the orientation (vertical/horizontal) of
+		 * the previous mouse wheel report. The input_events will be
+		 * generated once both reports are recorded in a4_event().
+		 */
+		return -1;
+	}
+
+	return 0;
+
+}
+
+static int a4_input_mapped(struct hid_device *hdev, struct hid_input *hi,
+		struct hid_field *field, struct hid_usage *usage,
+		unsigned long **bit, int *max)
+{
+	struct a4tech_sc *a4 = hid_get_drvdata(hdev);
+
+	if (usage->type == EV_REL && usage->code == REL_WHEEL_HI_RES) {
+		set_bit(REL_HWHEEL, *bit);
+		set_bit(REL_HWHEEL_HI_RES, *bit);
+	}
+
+	if ((a4->quirks & A4_2WHEEL_MOUSE_HACK_7) && usage->hid == 0x00090007)
+		return -1;
+
+	return 0;
+}
+
+static int a4_event(struct hid_device *hdev, struct hid_field *field,
+		struct hid_usage *usage, __s32 value)
+{
+	struct a4tech_sc *a4 = hid_get_drvdata(hdev);
+	struct input_dev *input;
+
+	if (!(hdev->claimed & HID_CLAIMED_INPUT) || !field->hidinput)
+		return 0;
+
+	input = field->hidinput->input;
+
+	if (a4->quirks & A4_2WHEEL_MOUSE_HACK_B8) {
+		if (usage->type == EV_REL && usage->code == REL_WHEEL_HI_RES) {
+			a4->delayed_value = value;
+			return 1;
+		}
+
+		if (usage->hid == A4_WHEEL_ORIENTATION) {
+			input_event(input, EV_REL, value ? REL_HWHEEL :
+					REL_WHEEL, a4->delayed_value);
+			input_event(input, EV_REL, value ? REL_HWHEEL_HI_RES :
+					REL_WHEEL_HI_RES, a4->delayed_value * 120);
+			return 1;
+		}
+	}
+
+	if ((a4->quirks & A4_2WHEEL_MOUSE_HACK_7) && usage->hid == 0x00090007) {
+		a4->hw_wheel = !!value;
+		return 1;
+	}
+
+	if (usage->code == REL_WHEEL_HI_RES && a4->hw_wheel) {
+		input_event(input, usage->type, REL_HWHEEL, value);
+		input_event(input, usage->type, REL_HWHEEL_HI_RES, value * 120);
+		return 1;
+	}
+
+	return 0;
+}
+
+static int a4_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	struct a4tech_sc *a4;
+	int ret;
+
+	a4 = devm_kzalloc(&hdev->dev, sizeof(*a4), GFP_KERNEL);
+	if (a4 == NULL) {
+		hid_err(hdev, "can't alloc device descriptor\n");
+		return -ENOMEM;
+	}
+
+	a4->quirks = id->driver_data;
+
+	hid_set_drvdata(hdev, a4);
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "parse failed\n");
+		return ret;
+	}
+
+	ret = hid_hw_start(hdev, HID_CONNECT_DEFAULT);
+	if (ret) {
+		hid_err(hdev, "hw start failed\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct hid_device_id a4_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_A4TECH, USB_DEVICE_ID_A4TECH_WCP32PU),
+		.driver_data = A4_2WHEEL_MOUSE_HACK_7 },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_A4TECH, USB_DEVICE_ID_A4TECH_X5_005D),
+		.driver_data = A4_2WHEEL_MOUSE_HACK_B8 },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_A4TECH, USB_DEVICE_ID_A4TECH_RP_649),
+		.driver_data = A4_2WHEEL_MOUSE_HACK_B8 },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_A4TECH, USB_DEVICE_ID_A4TECH_NB_95),
+		.driver_data = A4_2WHEEL_MOUSE_HACK_B8 },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, a4_devices);
+
+static struct hid_driver a4_driver = {
+	.name = "a4tech",
+	.id_table = a4_devices,
+	.input_mapping = a4_input_mapping,
+	.input_mapped = a4_input_mapped,
+	.event = a4_event,
+	.probe = a4_probe,
+};
+module_hid_driver(a4_driver);
+
+MODULE_DESCRIPTION("HID driver for some a4tech \"special\" devices");
+MODULE_LICENSE("GPL");