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, 173 insertions, 0 deletions

diff --git a/drivers/hid/hid-elecom.c b/drivers/hid/hid-elecom.c
new file mode 100644
index 000000000..37d88ce57
--- /dev/null
+++ b/drivers/hid/hid-elecom.c
@@ -0,0 +1,173 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  HID driver for ELECOM devices:
+ *  - BM084 Bluetooth Mouse
+ *  - EX-G Trackballs (M-XT3DRBK, M-XT3URBK, M-XT4DRBK)
+ *  - DEFT Trackballs (M-DT1DRBK, M-DT1URBK, M-DT2DRBK, M-DT2URBK)
+ *  - HUGE Trackballs (M-HT1DRBK, M-HT1URBK)
+ *  - HUGE Plus Trackball (M-HT1MRBK)
+ *
+ *  Copyright (c) 2010 Richard Nauber <Richard.Nauber@gmail.com>
+ *  Copyright (c) 2016 Yuxuan Shui <yshuiv7@gmail.com>
+ *  Copyright (c) 2017 Diego Elio Pettenò <flameeyes@flameeyes.eu>
+ *  Copyright (c) 2017 Alex Manoussakis <amanou@gnu.org>
+ *  Copyright (c) 2017 Tomasz Kramkowski <tk@the-tk.com>
+ *  Copyright (c) 2020 YOSHIOKA Takuma <lo48576@hard-wi.red>
+ *  Copyright (c) 2022 Takahiro Fujii <fujii@xaxxi.net>
+ */
+
+/*
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+/*
+ * Certain ELECOM mice misreport their button count meaning that they only work
+ * correctly with the ELECOM mouse assistant software which is unavailable for
+ * Linux. A four extra INPUT reports and a FEATURE report are described by the
+ * report descriptor but it does not appear that these enable software to
+ * control what the extra buttons map to. The only simple and straightforward
+ * solution seems to involve fixing up the report descriptor.
+ */
+#define MOUSE_BUTTONS_MAX 8
+static void mouse_button_fixup(struct hid_device *hdev,
+			       __u8 *rdesc, unsigned int rsize,
+			       unsigned int button_bit_count,
+			       unsigned int padding_bit,
+			       unsigned int button_report_size,
+			       unsigned int button_usage_maximum,
+			       int nbuttons)
+{
+	if (rsize < 32 || rdesc[button_bit_count] != 0x95 ||
+	    rdesc[button_report_size] != 0x75 ||
+	    rdesc[button_report_size + 1] != 0x01 ||
+	    rdesc[button_usage_maximum] != 0x29 || rdesc[padding_bit] != 0x75)
+		return;
+	hid_info(hdev, "Fixing up Elecom mouse button count\n");
+	nbuttons = clamp(nbuttons, 0, MOUSE_BUTTONS_MAX);
+	rdesc[button_bit_count + 1] = nbuttons;
+	rdesc[button_usage_maximum + 1] = nbuttons;
+	rdesc[padding_bit + 1] = MOUSE_BUTTONS_MAX - nbuttons;
+}
+
+static const __u8 *elecom_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+		unsigned int *rsize)
+{
+	switch (hdev->product) {
+	case USB_DEVICE_ID_ELECOM_BM084:
+		/* The BM084 Bluetooth mouse includes a non-existing horizontal
+		 * wheel in the HID descriptor. */
+		if (*rsize >= 48 && rdesc[46] == 0x05 && rdesc[47] == 0x0c) {
+			hid_info(hdev, "Fixing up Elecom BM084 report descriptor\n");
+			rdesc[47] = 0x00;
+		}
+		break;
+	case USB_DEVICE_ID_ELECOM_M_XGL20DLBK:
+		/*
+		 * Report descriptor format:
+		 * 20: button bit count
+		 * 28: padding bit count
+		 * 22: button report size
+		 * 14: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 20, 28, 22, 14, 8);
+		break;
+	case USB_DEVICE_ID_ELECOM_M_XT3URBK_00FB:
+	case USB_DEVICE_ID_ELECOM_M_XT3URBK_018F:
+	case USB_DEVICE_ID_ELECOM_M_XT3DRBK_00FC:
+	case USB_DEVICE_ID_ELECOM_M_XT4DRBK:
+		/*
+		 * Report descriptor format:
+		 * 12: button bit count
+		 * 30: padding bit count
+		 * 14: button report size
+		 * 20: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 12, 30, 14, 20, 6);
+		break;
+	case USB_DEVICE_ID_ELECOM_M_DT1URBK:
+	case USB_DEVICE_ID_ELECOM_M_DT1DRBK:
+	case USB_DEVICE_ID_ELECOM_M_HT1URBK_010C:
+	case USB_DEVICE_ID_ELECOM_M_HT1URBK_019B:
+	case USB_DEVICE_ID_ELECOM_M_HT1DRBK_010D:
+		/*
+		 * Report descriptor format:
+		 * 12: button bit count
+		 * 30: padding bit count
+		 * 14: button report size
+		 * 20: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 12, 30, 14, 20, 8);
+		break;
+	case USB_DEVICE_ID_ELECOM_M_XT3DRBK_018C:
+		/*
+		 * Report descriptor format:
+		 * 22: button bit count
+		 * 30: padding bit count
+		 * 24: button report size
+		 * 16: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 22, 30, 24, 16, 6);
+		break;
+	case USB_DEVICE_ID_ELECOM_M_DT2DRBK:
+	case USB_DEVICE_ID_ELECOM_M_HT1DRBK_011C:
+		/*
+		 * Report descriptor format:
+		 * 22: button bit count
+		 * 30: padding bit count
+		 * 24: button report size
+		 * 16: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 22, 30, 24, 16, 8);
+		break;
+	case USB_DEVICE_ID_ELECOM_M_HT1MRBK:
+	case USB_DEVICE_ID_ELECOM_M_HT1MRBK_01AB:
+	case USB_DEVICE_ID_ELECOM_M_HT1MRBK_01AC:
+		/*
+		 * Report descriptor format:
+		 * 24: button bit count
+		 * 28: padding bit count
+		 * 22: button report size
+		 * 16: button usage maximum
+		 */
+		mouse_button_fixup(hdev, rdesc, *rsize, 24, 28, 22, 16, 8);
+		break;
+	}
+	return rdesc;
+}
+
+static const struct hid_device_id elecom_devices[] = {
+	{ HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_BM084) },
+	{ HID_BLUETOOTH_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1MRBK_01AC) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XGL20DLBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XT3URBK_00FB) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XT3URBK_018F) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XT3DRBK_00FC) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XT3DRBK_018C) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_XT4DRBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT1URBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT1DRBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_DT2DRBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1URBK_010C) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1URBK_019B) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1DRBK_010D) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1DRBK_011C) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1MRBK) },
+	{ HID_USB_DEVICE(USB_VENDOR_ID_ELECOM, USB_DEVICE_ID_ELECOM_M_HT1MRBK_01AB) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, elecom_devices);
+
+static struct hid_driver elecom_driver = {
+	.name = "elecom",
+	.id_table = elecom_devices,
+	.report_fixup = elecom_report_fixup
+};
+module_hid_driver(elecom_driver);
+
+MODULE_DESCRIPTION("HID driver for ELECOM devices");
+MODULE_LICENSE("GPL");