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, 106 insertions, 0 deletions

diff --git a/drivers/hid/hid-viewsonic.c b/drivers/hid/hid-viewsonic.c
new file mode 100644
index 000000000..532bed88b
--- /dev/null
+++ b/drivers/hid/hid-viewsonic.c
@@ -0,0 +1,106 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ *  HID driver for ViewSonic devices not fully compliant with HID standard
+ *
+ *  Copyright (c) 2017 Nikolai Kondrashov
+ */
+
+/*
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+/* Size of the original descriptor of PD1011 signature pad */
+#define PD1011_RDESC_ORIG_SIZE	408
+
+/* Fixed report descriptor of PD1011 signature pad */
+static const __u8 pd1011_rdesc_fixed[] = {
+	0x05, 0x0D,             /*  Usage Page (Digitizer),             */
+	0x09, 0x01,             /*  Usage (Digitizer),                  */
+	0xA1, 0x01,             /*  Collection (Application),           */
+	0x85, 0x02,             /*      Report ID (2),                  */
+	0x09, 0x20,             /*      Usage (Stylus),                 */
+	0xA0,                   /*      Collection (Physical),          */
+	0x75, 0x10,             /*          Report Size (16),           */
+	0x95, 0x01,             /*          Report Count (1),           */
+	0xA4,                   /*          Push,                       */
+	0x05, 0x01,             /*          Usage Page (Desktop),       */
+	0x65, 0x13,             /*          Unit (Inch),                */
+	0x55, 0xFD,             /*          Unit Exponent (-3),         */
+	0x34,                   /*          Physical Minimum (0),       */
+	0x09, 0x30,             /*          Usage (X),                  */
+	0x46, 0x5D, 0x21,       /*          Physical Maximum (8541),    */
+	0x27, 0x80, 0xA9,
+		0x00, 0x00,     /*          Logical Maximum (43392),    */
+	0x81, 0x02,             /*          Input (Variable),           */
+	0x09, 0x31,             /*          Usage (Y),                  */
+	0x46, 0xDA, 0x14,       /*          Physical Maximum (5338),    */
+	0x26, 0xF0, 0x69,       /*          Logical Maximum (27120),    */
+	0x81, 0x02,             /*          Input (Variable),           */
+	0xB4,                   /*          Pop,                        */
+	0x14,                   /*          Logical Minimum (0),        */
+	0x25, 0x01,             /*          Logical Maximum (1),        */
+	0x75, 0x01,             /*          Report Size (1),            */
+	0x95, 0x01,             /*          Report Count (1),           */
+	0x81, 0x03,             /*          Input (Constant, Variable), */
+	0x09, 0x32,             /*          Usage (In Range),           */
+	0x09, 0x42,             /*          Usage (Tip Switch),         */
+	0x95, 0x02,             /*          Report Count (2),           */
+	0x81, 0x02,             /*          Input (Variable),           */
+	0x95, 0x05,             /*          Report Count (5),           */
+	0x81, 0x03,             /*          Input (Constant, Variable), */
+	0x75, 0x10,             /*          Report Size (16),           */
+	0x95, 0x01,             /*          Report Count (1),           */
+	0x09, 0x30,             /*          Usage (Tip Pressure),       */
+	0x15, 0x05,             /*          Logical Minimum (5),        */
+	0x26, 0xFF, 0x07,       /*          Logical Maximum (2047),     */
+	0x81, 0x02,             /*          Input (Variable),           */
+	0x75, 0x10,             /*          Report Size (16),           */
+	0x95, 0x01,             /*          Report Count (1),           */
+	0x81, 0x03,             /*          Input (Constant, Variable), */
+	0xC0,                   /*      End Collection,                 */
+	0xC0                    /*  End Collection                      */
+};
+
+static const __u8 *viewsonic_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+					  unsigned int *rsize)
+{
+	switch (hdev->product) {
+	case USB_DEVICE_ID_VIEWSONIC_PD1011:
+	case USB_DEVICE_ID_SIGNOTEC_VIEWSONIC_PD1011:
+		if (*rsize == PD1011_RDESC_ORIG_SIZE) {
+			*rsize = sizeof(pd1011_rdesc_fixed);
+			return pd1011_rdesc_fixed;
+		}
+		break;
+	}
+
+	return rdesc;
+}
+
+static const struct hid_device_id viewsonic_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_VIEWSONIC,
+				USB_DEVICE_ID_VIEWSONIC_PD1011) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_SIGNOTEC,
+				USB_DEVICE_ID_SIGNOTEC_VIEWSONIC_PD1011) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, viewsonic_devices);
+
+static struct hid_driver viewsonic_driver = {
+	.name = "viewsonic",
+	.id_table = viewsonic_devices,
+	.report_fixup = viewsonic_report_fixup,
+};
+module_hid_driver(viewsonic_driver);
+
+MODULE_DESCRIPTION("HID driver for ViewSonic devices not fully compliant with HID standard");
+MODULE_LICENSE("GPL");