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, 117 insertions, 0 deletions

diff --git a/drivers/hid/hid-hyperx.c b/drivers/hid/hid-hyperx.c
new file mode 100644
index 000000000..18d2dc24c
--- /dev/null
+++ b/drivers/hid/hid-hyperx.c
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  HID driver for the HyperX QuadCast 2 microphone
+ *
+ *  The tap-to-mute button is handled entirely in the device firmware: it gates
+ *  the audio internally and does not send the Telephony "Phone Mute" usage its
+ *  own report descriptor advertises.  The resulting mute state is only reported
+ *  through a vendor-defined collection, which hid-input cannot map, so the
+ *  button is invisible to userspace.
+ *
+ *  Copyright (c) 2026 Benjamin Blume <benjaminblume@posteo.de>
+ */
+
+#include <linux/hid.h>
+#include <linux/input.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+#define HYPERX_QC2_REPORT_ID	0x77
+#define HYPERX_QC2_EVENT_MUTE	0x06
+#define HYPERX_QC2_MUTE_LEN	3
+
+struct hyperx_drvdata {
+	struct input_dev *input;
+	bool muted;
+	bool have_state;
+};
+
+static int hyperx_input_configured(struct hid_device *hdev,
+				   struct hid_input *hi)
+{
+	struct hyperx_drvdata *drvdata = hid_get_drvdata(hdev);
+
+	/*
+	 * The device exposes several application collections.  Prefer the
+	 * telephony one, which already advertises KEY_MICMUTE, and fall back
+	 * to the first collection otherwise.
+	 */
+	if (!drvdata->input || test_bit(KEY_MICMUTE, hi->input->keybit)) {
+		drvdata->input = hi->input;
+		input_set_capability(drvdata->input, EV_KEY, KEY_MICMUTE);
+	}
+
+	return 0;
+}
+
+static int hyperx_raw_event(struct hid_device *hdev, struct hid_report *report,
+			    u8 *data, int size)
+{
+	struct hyperx_drvdata *drvdata = hid_get_drvdata(hdev);
+	bool muted;
+
+	if (!(hdev->claimed & HID_CLAIMED_INPUT) || !drvdata->input)
+		return 0;
+
+	if (size < HYPERX_QC2_MUTE_LEN || data[0] != HYPERX_QC2_REPORT_ID ||
+	    data[1] != HYPERX_QC2_EVENT_MUTE)
+		return 0;
+
+	muted = data[2];
+	if (drvdata->have_state && muted == drvdata->muted)
+		return 0;
+
+	drvdata->muted = muted;
+	drvdata->have_state = true;
+
+	/*
+	 * The device reports the resulting absolute state, while KEY_MICMUTE is
+	 * a momentary key that userspace acts on as a toggle.  Emit one
+	 * keypress per state change.
+	 */
+	input_report_key(drvdata->input, KEY_MICMUTE, 1);
+	input_sync(drvdata->input);
+	input_report_key(drvdata->input, KEY_MICMUTE, 0);
+	input_sync(drvdata->input);
+
+	return 0;
+}
+
+static int hyperx_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	struct hyperx_drvdata *drvdata;
+	int ret;
+
+	drvdata = devm_kzalloc(&hdev->dev, sizeof(*drvdata), GFP_KERNEL);
+	if (!drvdata)
+		return -ENOMEM;
+
+	hid_set_drvdata(hdev, drvdata);
+
+	ret = hid_parse(hdev);
+	if (ret)
+		return ret;
+
+	return hid_hw_start(hdev, HID_CONNECT_DEFAULT);
+}
+
+static const struct hid_device_id hyperx_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_HP,
+			 USB_PRODUCT_ID_HP_HYPERX_QUADCAST_2) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, hyperx_devices);
+
+static struct hid_driver hyperx_driver = {
+	.name			= "hyperx",
+	.id_table		= hyperx_devices,
+	.probe			= hyperx_probe,
+	.input_configured	= hyperx_input_configured,
+	.raw_event		= hyperx_raw_event,
+};
+module_hid_driver(hyperx_driver);
+
+MODULE_DESCRIPTION("HID driver for the HyperX QuadCast 2 microphone");
+MODULE_AUTHOR("Benjamin Blume <benjaminblume@posteo.de>");
+MODULE_LICENSE("GPL");