ftrace: Synchronize the initialization of ftrace_opsgrafted

There's some internal state that ftrace_ops needs to have set, but since
it can be declared outside of the ftrace.c code, it calls
ftrace_ops_init() on the ops in every global function. The issue is that
if two tasks call it on the same ops at the same time it is possible to
have the initialization of one corrupt the initialization of the other
call.

Create a ops_mutex to use to synchronize every initialization of the
ftrace_ops. The mutex is taken within checking the ftrace_ops flag that
states it was initializied but the flag is checked again after the mutex
has been taken. Checking first outside the mutex allows it to shortcut
having to take the mutex. But then the check needs to be done again after
the mute is taken in case of races.

Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home
Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock")
Reported-by: sashiko-bot@kernel.org
Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 112 insertions, 0 deletions

diff --git a/drivers/hid/hid-pxrc.c b/drivers/hid/hid-pxrc.c
new file mode 100644
index 000000000..71fe0c06d
--- /dev/null
+++ b/drivers/hid/hid-pxrc.c
@@ -0,0 +1,112 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * HID driver for PhoenixRC 8-axis flight controller
+ *
+ * Copyright (C) 2022 Marcus Folkesson <marcus.folkesson@gmail.com>
+ */
+
+#include <linux/device.h>
+#include <linux/hid.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+struct pxrc_priv {
+	u8 slider;
+	u8 dial;
+	bool alternate;
+};
+
+static const __u8 pxrc_rdesc_fixed[] = {
+	0x05, 0x01,        // Usage Page (Generic Desktop Ctrls)
+	0x09, 0x04,        // Usage (Joystick)
+	0xA1, 0x01,        // Collection (Application)
+	0x09, 0x01,        //   Usage (Pointer)
+	0xA1, 0x00,        //   Collection (Physical)
+	0x09, 0x30,        //     Usage (X)
+	0x09, 0x36,        //     Usage (Slider)
+	0x09, 0x31,        //     Usage (Y)
+	0x09, 0x32,        //     Usage (Z)
+	0x09, 0x33,        //     Usage (Rx)
+	0x09, 0x34,        //     Usage (Ry)
+	0x09, 0x35,        //     Usage (Rz)
+	0x09, 0x37,        //     Usage (Dial)
+	0x15, 0x00,        //     Logical Minimum (0)
+	0x26, 0xFF, 0x00,  //     Logical Maximum (255)
+	0x35, 0x00,        //     Physical Minimum (0)
+	0x46, 0xFF, 0x00,  //     Physical Maximum (255)
+	0x75, 0x08,        //     Report Size (8)
+	0x95, 0x08,        //     Report Count (8)
+	0x81, 0x02,        //     Input (Data,Var,Abs,No Wrap,Linear,Preferred State,No Null Position)
+	0xC0,              //   End Collection
+	0xC0,              // End Collection
+};
+
+static const __u8 *pxrc_report_fixup(struct hid_device *hdev, __u8 *rdesc,
+				     unsigned int *rsize)
+{
+	hid_info(hdev, "fixing up PXRC report descriptor\n");
+	*rsize = sizeof(pxrc_rdesc_fixed);
+	return pxrc_rdesc_fixed;
+}
+
+static int pxrc_raw_event(struct hid_device *hdev, struct hid_report *report,
+	 u8 *data, int size)
+{
+	struct pxrc_priv *priv = hid_get_drvdata(hdev);
+
+	if (priv->alternate)
+		priv->slider = data[7];
+	else
+		priv->dial = data[7];
+
+	data[1] = priv->slider;
+	data[7] = priv->dial;
+
+	priv->alternate = !priv->alternate;
+	return 0;
+}
+
+static int pxrc_probe(struct hid_device *hdev, const struct hid_device_id *id)
+{
+	int ret;
+	struct pxrc_priv *priv;
+
+	priv = devm_kzalloc(&hdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+	hid_set_drvdata(hdev, priv);
+
+	ret = hid_parse(hdev);
+	if (ret) {
+		hid_err(hdev, "parse failed\n");
+		return ret;
+	}
+
+	ret = hid_hw_start(hdev, HID_CONNECT_DEFAULT);
+	if (ret) {
+		hid_err(hdev, "hw start failed\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static const struct hid_device_id pxrc_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_MULTIPLE_1781, USB_DEVICE_ID_PHOENIXRC) },
+	{ /* sentinel */ }
+};
+MODULE_DEVICE_TABLE(hid, pxrc_devices);
+
+static struct hid_driver pxrc_driver = {
+	.name = "hid-pxrc",
+	.id_table = pxrc_devices,
+	.report_fixup = pxrc_report_fixup,
+	.probe = pxrc_probe,
+	.raw_event = pxrc_raw_event,
+};
+module_hid_driver(pxrc_driver);
+
+MODULE_AUTHOR("Marcus Folkesson <marcus.folkesson@gmail.com>");
+MODULE_DESCRIPTION("HID driver for PXRC 8-axis flight controller");
+MODULE_LICENSE("GPL");