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, 115 insertions, 0 deletions

diff --git a/drivers/hid/hid-emsff.c b/drivers/hid/hid-emsff.c
new file mode 100644
index 000000000..d8e559e05
--- /dev/null
+++ b/drivers/hid/hid-emsff.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Force feedback support for EMS Trio Linker Plus II
+ *
+ *  Copyright (c) 2010 Ignaz Forster <ignaz.forster@gmx.de>
+ */
+
+/*
+ */
+
+
+#include <linux/hid.h>
+#include <linux/input.h>
+#include <linux/module.h>
+
+#include "hid-ids.h"
+
+struct emsff_device {
+	struct hid_report *report;
+};
+
+static int emsff_play(struct input_dev *dev, void *data,
+			 struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct emsff_device *emsff = data;
+	int weak, strong;
+
+	weak = effect->u.rumble.weak_magnitude;
+	strong = effect->u.rumble.strong_magnitude;
+
+	dbg_hid("called with 0x%04x 0x%04x\n", strong, weak);
+
+	weak = weak * 0xff / 0xffff;
+	strong = strong * 0xff / 0xffff;
+
+	emsff->report->field[0]->value[1] = weak;
+	emsff->report->field[0]->value[2] = strong;
+
+	dbg_hid("running with 0x%02x 0x%02x\n", strong, weak);
+	hid_hw_request(hid, emsff->report, HID_REQ_SET_REPORT);
+
+	return 0;
+}
+
+static int ems_input_configured(struct hid_device *hid, struct hid_input *hidinput)
+{
+	struct emsff_device *emsff;
+	struct hid_report *report;
+	struct list_head *report_list =
+			&hid->report_enum[HID_OUTPUT_REPORT].report_list;
+	struct input_dev *dev = hidinput->input;
+	int error;
+
+	if (!list_is_first(&hidinput->list, &hid->inputs))
+		return 0;
+
+	report = list_first_entry_or_null(report_list, struct hid_report, list);
+	if (!report) {
+		hid_err(hid, "no output reports found\n");
+		return -ENODEV;
+	}
+	if (report->maxfield < 1) {
+		hid_err(hid, "no fields in the report\n");
+		return -ENODEV;
+	}
+
+	if (report->field[0]->report_count < 7) {
+		hid_err(hid, "not enough values in the field\n");
+		return -ENODEV;
+	}
+
+	emsff = kzalloc_obj(struct emsff_device);
+	if (!emsff)
+		return -ENOMEM;
+
+	emsff->report = report;
+	set_bit(FF_RUMBLE, dev->ffbit);
+
+	error = input_ff_create_memless(dev, emsff, emsff_play);
+	if (error) {
+		kfree(emsff);
+		return error;
+	}
+
+	emsff->report->field[0]->value[0] = 0x01;
+	emsff->report->field[0]->value[1] = 0x00;
+	emsff->report->field[0]->value[2] = 0x00;
+	emsff->report->field[0]->value[3] = 0x00;
+	emsff->report->field[0]->value[4] = 0x00;
+	emsff->report->field[0]->value[5] = 0x00;
+	emsff->report->field[0]->value[6] = 0x00;
+	hid_hw_request(hid, emsff->report, HID_REQ_SET_REPORT);
+
+	hid_info(hid, "force feedback for EMS based devices by Ignaz Forster <ignaz.forster@gmx.de>\n");
+
+	return 0;
+}
+
+static const struct hid_device_id ems_devices[] = {
+	{ HID_USB_DEVICE(USB_VENDOR_ID_EMS, USB_DEVICE_ID_EMS_TRIO_LINKER_PLUS_II) },
+	{ }
+};
+MODULE_DEVICE_TABLE(hid, ems_devices);
+
+static struct hid_driver ems_driver = {
+	.name = "hkems",
+	.id_table = ems_devices,
+	.input_configured = ems_input_configured,
+};
+module_hid_driver(ems_driver);
+
+MODULE_DESCRIPTION("Force feedback support for EMS Trio Linker Plus II");
+MODULE_LICENSE("GPL");
+