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, 55 insertions, 0 deletions

diff --git a/drivers/hid/hid-ortek.c b/drivers/hid/hid-ortek.c
new file mode 100644
index 000000000..f27297269
--- /dev/null
+++ b/drivers/hid/hid-ortek.c
@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  HID driver for various devices which are apparently based on the same chipset
+ *  from certain vendor which produces chips that contain wrong LogicalMaximum
+ *  value in their HID report descriptor. Currently supported devices are:
+ *
+ *    Ortek PKB-1700
+ *    Ortek WKB-2000
+ *    iHome IMAC-A210S
+ *    Skycable wireless presenter
+ *
+ *  Copyright (c) 2010 Johnathon Harris <jmharris@gmail.com>
+ *  Copyright (c) 2011 Jiri Kosina
+ */
+
+/*
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+static const __u8 *ortek_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+		unsigned int *rsize)
+{
+	if (*rsize >= 56 && rdesc[54] == 0x25 && rdesc[55] == 0x01) {
+		hid_info(hdev, "Fixing up logical maximum in report descriptor (Ortek)\n");
+		rdesc[55] = 0x92;
+	} else if (*rsize >= 54 && rdesc[52] == 0x25 && rdesc[53] == 0x01) {
+		hid_info(hdev, "Fixing up logical maximum in report descriptor (Skycable)\n");
+		rdesc[53] = 0x65;
+	}
+	return rdesc;
+}
+
+static const struct hid_device_id ortek_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ORTEK, USB_DEVICE_ID_ORTEK_PKB1700) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ORTEK, USB_DEVICE_ID_ORTEK_WKB2000) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ORTEK, USB_DEVICE_ID_ORTEK_IHOME_IMAC_A210S) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_SKYCABLE, USB_DEVICE_ID_SKYCABLE_WIRELESS_PRESENTER) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, ortek_devices);
+
+static struct hid_driver ortek_driver = {
+	.name = "ortek",
+	.id_table = ortek_devices,
+	.report_fixup = ortek_report_fixup
+};
+module_hid_driver(ortek_driver);
+
+MODULE_DESCRIPTION("HID driver for Ortek PKB-1700/WKB-2000/Skycable wireless keyboard and mouse trackpad");
+MODULE_LICENSE("GPL");