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, 190 insertions, 0 deletions

diff --git a/drivers/usb/misc/ehset.c b/drivers/usb/misc/ehset.c
new file mode 100644
index 000000000..36b6e9fa7
--- /dev/null
+++ b/drivers/usb/misc/ehset.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2010-2013, The Linux Foundation. All rights reserved.
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/usb.h>
+#include <linux/usb/ch11.h>
+
+#define TEST_SE0_NAK_PID			0x0101
+#define TEST_J_PID				0x0102
+#define TEST_K_PID				0x0103
+#define TEST_PACKET_PID				0x0104
+#define TEST_HS_HOST_PORT_SUSPEND_RESUME	0x0106
+#define TEST_SINGLE_STEP_GET_DEV_DESC		0x0107
+#define TEST_SINGLE_STEP_SET_FEATURE		0x0108
+
+extern const struct usb_device_id *usb_device_match_id(struct usb_device *udev,
+						const struct usb_device_id *id);
+
+/*
+ * A list of USB hubs which requires to disable the power
+ * to the port before starting the testing procedures.
+ */
+static const struct usb_device_id ehset_hub_list[] = {
+	{ USB_DEVICE(0x0424, 0x4502) },
+	{ USB_DEVICE(0x0424, 0x4913) },
+	{ USB_DEVICE(0x0451, 0x8027) },
+	{ }
+};
+
+static int ehset_prepare_port_for_testing(struct usb_device *hub_udev, u16 portnum)
+{
+	int ret = 0;
+
+	/*
+	 * The USB2.0 spec chapter 11.24.2.13 says that the USB port which is
+	 * going under test needs to be put in suspend before sending the
+	 * test command. Most hubs don't enforce this precondition, but there
+	 * are some hubs which needs to disable the power to the port before
+	 * starting the test.
+	 */
+	if (usb_device_match_id(hub_udev, ehset_hub_list)) {
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_CLEAR_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_ENABLE,
+					   portnum, NULL, 0, 1000, GFP_KERNEL);
+		/*
+		 * Wait for the port to be disabled. It's an arbitrary value
+		 * which worked every time.
+		 */
+		msleep(100);
+	} else {
+		/*
+		 * For the hubs which are compliant with the spec,
+		 * put the port in SUSPEND.
+		 */
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_SET_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_SUSPEND,
+					   portnum, NULL, 0, 1000, GFP_KERNEL);
+	}
+	return ret;
+}
+
+static int ehset_probe(struct usb_interface *intf,
+		       const struct usb_device_id *id)
+{
+	int ret = -EINVAL;
+	struct usb_device *dev = interface_to_usbdev(intf);
+	struct usb_device *hub_udev = dev->parent;
+	struct usb_device_descriptor buf;
+	u8 portnum = dev->portnum;
+	u16 test_pid = le16_to_cpu(dev->descriptor.idProduct);
+
+	switch (test_pid) {
+	case TEST_SE0_NAK_PID:
+		ret = ehset_prepare_port_for_testing(hub_udev, portnum);
+		if (ret < 0)
+			break;
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_SET_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_TEST,
+					   (USB_TEST_SE0_NAK << 8) | portnum,
+					   NULL, 0, 1000, GFP_KERNEL);
+		break;
+	case TEST_J_PID:
+		ret = ehset_prepare_port_for_testing(hub_udev, portnum);
+		if (ret < 0)
+			break;
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_SET_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_TEST,
+					   (USB_TEST_J << 8) | portnum, NULL, 0,
+					   1000, GFP_KERNEL);
+		break;
+	case TEST_K_PID:
+		ret = ehset_prepare_port_for_testing(hub_udev, portnum);
+		if (ret < 0)
+			break;
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_SET_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_TEST,
+					   (USB_TEST_K << 8) | portnum, NULL, 0,
+					   1000, GFP_KERNEL);
+		break;
+	case TEST_PACKET_PID:
+		ret = ehset_prepare_port_for_testing(hub_udev, portnum);
+		if (ret < 0)
+			break;
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_SET_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_TEST,
+					   (USB_TEST_PACKET << 8) | portnum,
+					   NULL, 0, 1000, GFP_KERNEL);
+		break;
+	case TEST_HS_HOST_PORT_SUSPEND_RESUME:
+		/* Test: wait for 15secs -> suspend -> 15secs delay -> resume */
+		msleep(15 * 1000);
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_SET_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_SUSPEND,
+					   portnum, NULL, 0, 1000, GFP_KERNEL);
+		if (ret < 0)
+			break;
+
+		msleep(15 * 1000);
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_CLEAR_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_SUSPEND,
+					   portnum, NULL, 0, 1000, GFP_KERNEL);
+		break;
+	case TEST_SINGLE_STEP_GET_DEV_DESC:
+		/* Test: wait for 15secs -> GetDescriptor request */
+		msleep(15 * 1000);
+
+		ret = usb_control_msg_recv(dev, 0, USB_REQ_GET_DESCRIPTOR,
+					   USB_DIR_IN, USB_DT_DEVICE << 8, 0,
+					   &buf, USB_DT_DEVICE_SIZE,
+					   USB_CTRL_GET_TIMEOUT, GFP_KERNEL);
+		break;
+	case TEST_SINGLE_STEP_SET_FEATURE:
+		/*
+		 * GetDescriptor SETUP request -> 15secs delay -> IN & STATUS
+		 *
+		 * Note, this test is only supported on root hubs since the
+		 * SetPortFeature handling can only be done inside the HCD's
+		 * hub_control callback function.
+		 */
+		if (hub_udev != dev->bus->root_hub) {
+			dev_err(&intf->dev, "SINGLE_STEP_SET_FEATURE test only supported on root hub\n");
+			break;
+		}
+
+		ret = usb_control_msg_send(hub_udev, 0, USB_REQ_SET_FEATURE,
+					   USB_RT_PORT, USB_PORT_FEAT_TEST,
+					   (6 << 8) | portnum, NULL, 0,
+					   60 * 1000, GFP_KERNEL);
+
+		break;
+	default:
+		dev_err(&intf->dev, "%s: unsupported PID: 0x%x\n",
+			__func__, test_pid);
+	}
+
+	return ret;
+}
+
+static void ehset_disconnect(struct usb_interface *intf)
+{
+}
+
+static const struct usb_device_id ehset_id_table[] = {
+	{ USB_DEVICE(0x1a0a, TEST_SE0_NAK_PID) },
+	{ USB_DEVICE(0x1a0a, TEST_J_PID) },
+	{ USB_DEVICE(0x1a0a, TEST_K_PID) },
+	{ USB_DEVICE(0x1a0a, TEST_PACKET_PID) },
+	{ USB_DEVICE(0x1a0a, TEST_HS_HOST_PORT_SUSPEND_RESUME) },
+	{ USB_DEVICE(0x1a0a, TEST_SINGLE_STEP_GET_DEV_DESC) },
+	{ USB_DEVICE(0x1a0a, TEST_SINGLE_STEP_SET_FEATURE) },
+	{ }			/* Terminating entry */
+};
+MODULE_DEVICE_TABLE(usb, ehset_id_table);
+
+static struct usb_driver ehset_driver = {
+	.name =		"usb_ehset_test",
+	.probe =	ehset_probe,
+	.disconnect =	ehset_disconnect,
+	.id_table =	ehset_id_table,
+};
+
+module_usb_driver(ehset_driver);
+
+MODULE_DESCRIPTION("USB Driver for EHSET Test Fixture");
+MODULE_LICENSE("GPL v2");