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, 254 insertions, 0 deletions

diff --git a/drivers/input/tablet/acecad.c b/drivers/input/tablet/acecad.c
new file mode 100644
index 000000000..ba79dff21
--- /dev/null
+++ b/drivers/input/tablet/acecad.c
@@ -0,0 +1,254 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2001-2005 Edouard TISSERANT   <edouard.tisserant@wanadoo.fr>
+ *  Copyright (c) 2004-2005 Stephane VOLTZ      <svoltz@numericable.fr>
+ *
+ *  USB Acecad "Acecad Flair" tablet support
+ *
+ *  Changelog:
+ *      v3.2 - Added sysfs support
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb/input.h>
+
+MODULE_AUTHOR("Edouard TISSERANT <edouard.tisserant@wanadoo.fr>");
+MODULE_DESCRIPTION("USB Acecad Flair tablet driver");
+MODULE_LICENSE("GPL");
+
+#define USB_VENDOR_ID_ACECAD	0x0460
+#define USB_DEVICE_ID_FLAIR	0x0004
+#define USB_DEVICE_ID_302	0x0008
+
+struct usb_acecad {
+	char name[128];
+	char phys[64];
+	struct usb_interface *intf;
+	struct input_dev *input;
+	struct urb *irq;
+
+	unsigned char *data;
+	dma_addr_t data_dma;
+};
+
+static void usb_acecad_irq(struct urb *urb)
+{
+	struct usb_acecad *acecad = urb->context;
+	unsigned char *data = acecad->data;
+	struct input_dev *dev = acecad->input;
+	struct usb_interface *intf = acecad->intf;
+	struct usb_device *udev = interface_to_usbdev(intf);
+	int prox, status;
+
+	switch (urb->status) {
+	case 0:
+		/* success */
+		break;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* this urb is terminated, clean up */
+		dev_dbg(&intf->dev, "%s - urb shutting down with status: %d\n",
+			__func__, urb->status);
+		return;
+	default:
+		dev_dbg(&intf->dev, "%s - nonzero urb status received: %d\n",
+			__func__, urb->status);
+		goto resubmit;
+	}
+
+	prox = (data[0] & 0x04) >> 2;
+	input_report_key(dev, BTN_TOOL_PEN, prox);
+
+	if (prox) {
+		int x = data[1] | (data[2] << 8);
+		int y = data[3] | (data[4] << 8);
+		/* Pressure should compute the same way for flair and 302 */
+		int pressure = data[5] | (data[6] << 8);
+		int touch = data[0] & 0x01;
+		int stylus = (data[0] & 0x10) >> 4;
+		int stylus2 = (data[0] & 0x20) >> 5;
+		input_report_abs(dev, ABS_X, x);
+		input_report_abs(dev, ABS_Y, y);
+		input_report_abs(dev, ABS_PRESSURE, pressure);
+		input_report_key(dev, BTN_TOUCH, touch);
+		input_report_key(dev, BTN_STYLUS, stylus);
+		input_report_key(dev, BTN_STYLUS2, stylus2);
+	}
+
+	/* event termination */
+	input_sync(dev);
+
+resubmit:
+	status = usb_submit_urb(urb, GFP_ATOMIC);
+	if (status)
+		dev_err(&intf->dev,
+			"can't resubmit intr, %s-%s/input0, status %d\n",
+			udev->bus->bus_name,
+			udev->devpath, status);
+}
+
+static int usb_acecad_open(struct input_dev *dev)
+{
+	struct usb_acecad *acecad = input_get_drvdata(dev);
+
+	acecad->irq->dev = interface_to_usbdev(acecad->intf);
+	if (usb_submit_urb(acecad->irq, GFP_KERNEL))
+		return -EIO;
+
+	return 0;
+}
+
+static void usb_acecad_close(struct input_dev *dev)
+{
+	struct usb_acecad *acecad = input_get_drvdata(dev);
+
+	usb_kill_urb(acecad->irq);
+}
+
+static int usb_acecad_probe(struct usb_interface *intf, const struct usb_device_id *id)
+{
+	struct usb_device *dev = interface_to_usbdev(intf);
+	struct usb_host_interface *interface = intf->cur_altsetting;
+	struct usb_endpoint_descriptor *endpoint;
+	struct usb_acecad *acecad;
+	struct input_dev *input_dev;
+	int pipe, maxp;
+	int err;
+
+	if (interface->desc.bNumEndpoints != 1)
+		return -ENODEV;
+
+	endpoint = &interface->endpoint[0].desc;
+
+	if (!usb_endpoint_is_int_in(endpoint))
+		return -ENODEV;
+
+	pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress);
+	maxp = usb_maxpacket(dev, pipe);
+
+	acecad = kzalloc_obj(*acecad);
+	input_dev = input_allocate_device();
+	if (!acecad || !input_dev) {
+		err = -ENOMEM;
+		goto fail1;
+	}
+
+	acecad->data = usb_alloc_coherent(dev, 8, GFP_KERNEL, &acecad->data_dma);
+	if (!acecad->data) {
+		err= -ENOMEM;
+		goto fail1;
+	}
+
+	acecad->irq = usb_alloc_urb(0, GFP_KERNEL);
+	if (!acecad->irq) {
+		err = -ENOMEM;
+		goto fail2;
+	}
+
+	acecad->intf = intf;
+	acecad->input = input_dev;
+
+	if (dev->manufacturer)
+		strscpy(acecad->name, dev->manufacturer, sizeof(acecad->name));
+
+	if (dev->product) {
+		if (dev->manufacturer)
+			strlcat(acecad->name, " ", sizeof(acecad->name));
+		strlcat(acecad->name, dev->product, sizeof(acecad->name));
+	}
+
+	usb_make_path(dev, acecad->phys, sizeof(acecad->phys));
+	strlcat(acecad->phys, "/input0", sizeof(acecad->phys));
+
+	input_dev->name = acecad->name;
+	input_dev->phys = acecad->phys;
+	usb_to_input_id(dev, &input_dev->id);
+	input_dev->dev.parent = &intf->dev;
+
+	input_set_drvdata(input_dev, acecad);
+
+	input_dev->open = usb_acecad_open;
+	input_dev->close = usb_acecad_close;
+
+	input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_DIGI)] = BIT_MASK(BTN_TOOL_PEN) |
+		BIT_MASK(BTN_TOUCH) | BIT_MASK(BTN_STYLUS) |
+		BIT_MASK(BTN_STYLUS2);
+
+	switch (id->driver_info) {
+	case 0:
+		input_set_abs_params(input_dev, ABS_X, 0, 5000, 4, 0);
+		input_set_abs_params(input_dev, ABS_Y, 0, 3750, 4, 0);
+		input_set_abs_params(input_dev, ABS_PRESSURE, 0, 512, 0, 0);
+		if (!strlen(acecad->name))
+			snprintf(acecad->name, sizeof(acecad->name),
+				"USB Acecad Flair Tablet %04x:%04x",
+				le16_to_cpu(dev->descriptor.idVendor),
+				le16_to_cpu(dev->descriptor.idProduct));
+		break;
+
+	case 1:
+		input_set_abs_params(input_dev, ABS_X, 0, 53000, 4, 0);
+		input_set_abs_params(input_dev, ABS_Y, 0, 2250, 4, 0);
+		input_set_abs_params(input_dev, ABS_PRESSURE, 0, 1024, 0, 0);
+		if (!strlen(acecad->name))
+			snprintf(acecad->name, sizeof(acecad->name),
+				"USB Acecad 302 Tablet %04x:%04x",
+				le16_to_cpu(dev->descriptor.idVendor),
+				le16_to_cpu(dev->descriptor.idProduct));
+		break;
+	}
+
+	usb_fill_int_urb(acecad->irq, dev, pipe,
+			acecad->data, maxp > 8 ? 8 : maxp,
+			usb_acecad_irq, acecad, endpoint->bInterval);
+	acecad->irq->transfer_dma = acecad->data_dma;
+	acecad->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+
+	err = input_register_device(acecad->input);
+	if (err)
+		goto fail3;
+
+	usb_set_intfdata(intf, acecad);
+
+	return 0;
+
+ fail3:	usb_free_urb(acecad->irq);
+ fail2:	usb_free_coherent(dev, 8, acecad->data, acecad->data_dma);
+ fail1: input_free_device(input_dev);
+	kfree(acecad);
+	return err;
+}
+
+static void usb_acecad_disconnect(struct usb_interface *intf)
+{
+	struct usb_acecad *acecad = usb_get_intfdata(intf);
+	struct usb_device *udev = interface_to_usbdev(intf);
+
+	usb_set_intfdata(intf, NULL);
+
+	input_unregister_device(acecad->input);
+	usb_free_urb(acecad->irq);
+	usb_free_coherent(udev, 8, acecad->data, acecad->data_dma);
+	kfree(acecad);
+}
+
+static const struct usb_device_id usb_acecad_id_table[] = {
+	{ USB_DEVICE(USB_VENDOR_ID_ACECAD, USB_DEVICE_ID_FLAIR), .driver_info = 0 },
+	{ USB_DEVICE(USB_VENDOR_ID_ACECAD, USB_DEVICE_ID_302),	 .driver_info = 1 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(usb, usb_acecad_id_table);
+
+static struct usb_driver usb_acecad_driver = {
+	.name =		"usb_acecad",
+	.probe =	usb_acecad_probe,
+	.disconnect =	usb_acecad_disconnect,
+	.id_table =	usb_acecad_id_table,
+};
+
+module_usb_driver(usb_acecad_driver);