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, 115 insertions, 0 deletions

diff --git a/drivers/hid/hid-emsff.c b/drivers/hid/hid-emsff.c
new file mode 100644
index 000000000..d8e559e05
--- /dev/null
+++ b/drivers/hid/hid-emsff.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Force feedback support for EMS Trio Linker Plus II
+ *
+ *  Copyright (c) 2010 Ignaz Forster <ignaz.forster@gmx.de>
+ */
+
+/*
+ */
+
+
+#include <linux/hid.h>
+#include <linux/input.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+struct emsff_device {
+	struct hid_report *report;
+};
+
+static int emsff_play(struct input_dev *dev, void *data,
+			 struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct emsff_device *emsff = data;
+	int weak, strong;
+
+	weak = effect->u.rumble.weak_magnitude;
+	strong = effect->u.rumble.strong_magnitude;
+
+	dbg_hid("called with 0x%04x 0x%04x\n", strong, weak);
+
+	weak = weak * 0xff / 0xffff;
+	strong = strong * 0xff / 0xffff;
+
+	emsff->report->field[0]->value[1] = weak;
+	emsff->report->field[0]->value[2] = strong;
+
+	dbg_hid("running with 0x%02x 0x%02x\n", strong, weak);
+	hid_hw_request(hid, emsff->report, HID_REQ_SET_REPORT);
+
+	return 0;
+}
+
+static int ems_input_configured(struct hid_device *hid, struct hid_input *hidinput)
+{
+	struct emsff_device *emsff;
+	struct hid_report *report;
+	struct list_head *report_list =
+			&hid->report_enum[HID_OUTPUT_REPORT].report_list;
+	struct input_dev *dev = hidinput->input;
+	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;
+	}
+	if (report->maxfield < 1) {
+		hid_err(hid, "no fields in the report\n");
+		return -ENODEV;
+	}
+
+	if (report->field[0]->report_count < 7) {
+		hid_err(hid, "not enough values in the field\n");
+		return -ENODEV;
+	}
+
+	emsff = kzalloc_obj(struct emsff_device);
+	if (!emsff)
+		return -ENOMEM;
+
+	emsff->report = report;
+	set_bit(FF_RUMBLE, dev->ffbit);
+
+	error = input_ff_create_memless(dev, emsff, emsff_play);
+	if (error) {
+		kfree(emsff);
+		return error;
+	}
+
+	emsff->report->field[0]->value[0] = 0x01;
+	emsff->report->field[0]->value[1] = 0x00;
+	emsff->report->field[0]->value[2] = 0x00;
+	emsff->report->field[0]->value[3] = 0x00;
+	emsff->report->field[0]->value[4] = 0x00;
+	emsff->report->field[0]->value[5] = 0x00;
+	emsff->report->field[0]->value[6] = 0x00;
+	hid_hw_request(hid, emsff->report, HID_REQ_SET_REPORT);
+
+	hid_info(hid, "force feedback for EMS based devices by Ignaz Forster <ignaz.forster@gmx.de>\n");
+
+	return 0;
+}
+
+static const struct hid_device_id ems_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_EMS, USB_DEVICE_ID_EMS_TRIO_LINKER_PLUS_II) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, ems_devices);
+
+static struct hid_driver ems_driver = {
+	.name = "hkems",
+	.id_table = ems_devices,
+	.input_configured = ems_input_configured,
+};
+module_hid_driver(ems_driver);
+
+MODULE_DESCRIPTION("Force feedback support for EMS Trio Linker Plus II");
+MODULE_LICENSE("GPL");
+