sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.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");