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, 204 insertions, 0 deletions

diff --git a/drivers/input/tablet/kbtab.c b/drivers/input/tablet/kbtab.c
new file mode 100644
index 000000000..6ce70c8e2
--- /dev/null
+++ b/drivers/input/tablet/kbtab.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb/input.h>
+#include <linux/unaligned.h>
+
+/*
+ * Pressure-threshold modules param code from Alex Perry <alex.perry@ieee.org>
+ */
+
+MODULE_AUTHOR("Josh Myer <josh@joshisanerd.com>");
+MODULE_DESCRIPTION("USB KB Gear JamStudio Tablet driver");
+MODULE_LICENSE("GPL");
+
+#define USB_VENDOR_ID_KBGEAR	0x084e
+
+static int kb_pressure_click = 0x10;
+module_param(kb_pressure_click, int, 0);
+MODULE_PARM_DESC(kb_pressure_click, "pressure threshold for clicks");
+
+struct kbtab {
+	unsigned char *data;
+	dma_addr_t data_dma;
+	struct input_dev *dev;
+	struct usb_interface *intf;
+	struct urb *irq;
+	char phys[32];
+};
+
+static void kbtab_irq(struct urb *urb)
+{
+	struct kbtab *kbtab = urb->context;
+	unsigned char *data = kbtab->data;
+	struct input_dev *dev = kbtab->dev;
+	int pressure;
+	int retval;
+
+	switch (urb->status) {
+	case 0:
+		/* success */
+		break;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* this urb is terminated, clean up */
+		dev_dbg(&kbtab->intf->dev,
+			"%s - urb shutting down with status: %d\n",
+			__func__, urb->status);
+		return;
+	default:
+		dev_dbg(&kbtab->intf->dev,
+			"%s - nonzero urb status received: %d\n",
+			__func__, urb->status);
+		goto exit;
+	}
+
+
+	input_report_key(dev, BTN_TOOL_PEN, 1);
+
+	input_report_abs(dev, ABS_X, get_unaligned_le16(&data[1]));
+	input_report_abs(dev, ABS_Y, get_unaligned_le16(&data[3]));
+
+	/*input_report_key(dev, BTN_TOUCH , data[0] & 0x01);*/
+	input_report_key(dev, BTN_RIGHT, data[0] & 0x02);
+
+	pressure = data[5];
+	if (kb_pressure_click == -1)
+		input_report_abs(dev, ABS_PRESSURE, pressure);
+	else
+		input_report_key(dev, BTN_LEFT, pressure > kb_pressure_click ? 1 : 0);
+
+	input_sync(dev);
+
+ exit:
+	retval = usb_submit_urb(urb, GFP_ATOMIC);
+	if (retval)
+		dev_err(&kbtab->intf->dev,
+			"%s - usb_submit_urb failed with result %d\n",
+			__func__, retval);
+}
+
+static const struct usb_device_id kbtab_ids[] = {
+	{ USB_DEVICE(USB_VENDOR_ID_KBGEAR, 0x1001), .driver_info = 0 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(usb, kbtab_ids);
+
+static int kbtab_open(struct input_dev *dev)
+{
+	struct kbtab *kbtab = input_get_drvdata(dev);
+	struct usb_device *udev = interface_to_usbdev(kbtab->intf);
+
+	kbtab->irq->dev = udev;
+	if (usb_submit_urb(kbtab->irq, GFP_KERNEL))
+		return -EIO;
+
+	return 0;
+}
+
+static void kbtab_close(struct input_dev *dev)
+{
+	struct kbtab *kbtab = input_get_drvdata(dev);
+
+	usb_kill_urb(kbtab->irq);
+}
+
+static int kbtab_probe(struct usb_interface *intf, const struct usb_device_id *id)
+{
+	struct usb_device *dev = interface_to_usbdev(intf);
+	struct usb_endpoint_descriptor *endpoint;
+	struct kbtab *kbtab;
+	struct input_dev *input_dev;
+	int error = -ENOMEM;
+
+	if (intf->cur_altsetting->desc.bNumEndpoints < 1)
+		return -ENODEV;
+
+	endpoint = &intf->cur_altsetting->endpoint[0].desc;
+	if (!usb_endpoint_is_int_in(endpoint))
+		return -ENODEV;
+
+	kbtab = kzalloc_obj(*kbtab);
+	input_dev = input_allocate_device();
+	if (!kbtab || !input_dev)
+		goto fail1;
+
+	kbtab->data = usb_alloc_coherent(dev, 8, GFP_KERNEL, &kbtab->data_dma);
+	if (!kbtab->data)
+		goto fail1;
+
+	kbtab->irq = usb_alloc_urb(0, GFP_KERNEL);
+	if (!kbtab->irq)
+		goto fail2;
+
+	kbtab->intf = intf;
+	kbtab->dev = input_dev;
+
+	usb_make_path(dev, kbtab->phys, sizeof(kbtab->phys));
+	strlcat(kbtab->phys, "/input0", sizeof(kbtab->phys));
+
+	input_dev->name = "KB Gear Tablet";
+	input_dev->phys = kbtab->phys;
+	usb_to_input_id(dev, &input_dev->id);
+	input_dev->dev.parent = &intf->dev;
+
+	input_set_drvdata(input_dev, kbtab);
+
+	input_dev->open = kbtab_open;
+	input_dev->close = kbtab_close;
+
+	input_dev->evbit[0] |= BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_LEFT)] |=
+		BIT_MASK(BTN_LEFT) | BIT_MASK(BTN_RIGHT);
+	input_dev->keybit[BIT_WORD(BTN_DIGI)] |=
+		BIT_MASK(BTN_TOOL_PEN) | BIT_MASK(BTN_TOUCH);
+	input_set_abs_params(input_dev, ABS_X, 0, 0x2000, 4, 0);
+	input_set_abs_params(input_dev, ABS_Y, 0, 0x1750, 4, 0);
+	input_set_abs_params(input_dev, ABS_PRESSURE, 0, 0xff, 0, 0);
+
+	usb_fill_int_urb(kbtab->irq, dev,
+			 usb_rcvintpipe(dev, endpoint->bEndpointAddress),
+			 kbtab->data, 8,
+			 kbtab_irq, kbtab, endpoint->bInterval);
+	kbtab->irq->transfer_dma = kbtab->data_dma;
+	kbtab->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+
+	error = input_register_device(kbtab->dev);
+	if (error)
+		goto fail3;
+
+	usb_set_intfdata(intf, kbtab);
+
+	return 0;
+
+ fail3:	usb_free_urb(kbtab->irq);
+ fail2:	usb_free_coherent(dev, 8, kbtab->data, kbtab->data_dma);
+ fail1:	input_free_device(input_dev);
+	kfree(kbtab);
+	return error;
+}
+
+static void kbtab_disconnect(struct usb_interface *intf)
+{
+	struct kbtab *kbtab = usb_get_intfdata(intf);
+	struct usb_device *udev = interface_to_usbdev(intf);
+
+	usb_set_intfdata(intf, NULL);
+
+	input_unregister_device(kbtab->dev);
+	usb_free_urb(kbtab->irq);
+	usb_free_coherent(udev, 8, kbtab->data, kbtab->data_dma);
+	kfree(kbtab);
+}
+
+static struct usb_driver kbtab_driver = {
+	.name =		"kbtab",
+	.probe =	kbtab_probe,
+	.disconnect =	kbtab_disconnect,
+	.id_table =	kbtab_ids,
+};
+
+module_usb_driver(kbtab_driver);