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, 121 insertions, 0 deletions

diff --git a/drivers/power/reset/qemu-virt-ctrl.c b/drivers/power/reset/qemu-virt-ctrl.c
new file mode 100644
index 000000000..97875007f
--- /dev/null
+++ b/drivers/power/reset/qemu-virt-ctrl.c
@@ -0,0 +1,121 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * QEMU Virt Machine System Controller Driver
+ *
+ * Copyright (C) 2026 Kuan-Wei Chiu <visitorckw@gmail.com>
+ */
+
+#include <linux/io.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/reboot.h>
+
+/* Registers */
+#define VIRT_CTRL_REG_FEATURES	0x00
+#define VIRT_CTRL_REG_CMD	0x04
+
+/* Commands */
+#define CMD_NOOP	0
+#define CMD_RESET	1
+#define CMD_HALT	2
+#define CMD_PANIC	3
+
+struct qemu_virt_ctrl {
+	void __iomem *base;
+	struct notifier_block reboot_nb;
+};
+
+static inline void virt_ctrl_write32(u32 val, void __iomem *addr)
+{
+	if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
+		iowrite32be(val, addr);
+	else
+		iowrite32(val, addr);
+}
+
+static int qemu_virt_ctrl_power_off(struct sys_off_data *data)
+{
+	struct qemu_virt_ctrl *ctrl = data->cb_data;
+
+	virt_ctrl_write32(CMD_HALT, ctrl->base + VIRT_CTRL_REG_CMD);
+
+	return NOTIFY_DONE;
+}
+
+static int qemu_virt_ctrl_restart(struct sys_off_data *data)
+{
+	struct qemu_virt_ctrl *ctrl = data->cb_data;
+
+	virt_ctrl_write32(CMD_RESET, ctrl->base + VIRT_CTRL_REG_CMD);
+
+	return NOTIFY_DONE;
+}
+
+static int qemu_virt_ctrl_reboot_notify(struct notifier_block *nb,
+					unsigned long action, void *data)
+{
+	struct qemu_virt_ctrl *ctrl = container_of(nb, struct qemu_virt_ctrl, reboot_nb);
+
+	if (action == SYS_HALT)
+		virt_ctrl_write32(CMD_HALT, ctrl->base + VIRT_CTRL_REG_CMD);
+
+	return NOTIFY_DONE;
+}
+
+static int qemu_virt_ctrl_probe(struct platform_device *pdev)
+{
+	struct qemu_virt_ctrl *ctrl;
+	int ret;
+
+	ctrl = devm_kzalloc(&pdev->dev, sizeof(*ctrl), GFP_KERNEL);
+	if (!ctrl)
+		return -ENOMEM;
+
+	ctrl->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(ctrl->base))
+		return PTR_ERR(ctrl->base);
+
+	ret = devm_register_sys_off_handler(&pdev->dev,
+					    SYS_OFF_MODE_RESTART,
+					    SYS_OFF_PRIO_DEFAULT,
+					    qemu_virt_ctrl_restart,
+					    ctrl);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret,
+				     "cannot register restart handler\n");
+
+	ret = devm_register_sys_off_handler(&pdev->dev,
+					    SYS_OFF_MODE_POWER_OFF,
+					    SYS_OFF_PRIO_DEFAULT,
+					    qemu_virt_ctrl_power_off,
+					    ctrl);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret,
+				     "cannot register power-off handler\n");
+
+	ctrl->reboot_nb.notifier_call = qemu_virt_ctrl_reboot_notify;
+	ret = devm_register_reboot_notifier(&pdev->dev, &ctrl->reboot_nb);
+	if (ret)
+		return dev_err_probe(&pdev->dev, ret, "cannot register reboot notifier\n");
+
+	return 0;
+}
+
+static const struct platform_device_id qemu_virt_ctrl_id[] = {
+	{ .name = "qemu-virt-ctrl" },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, qemu_virt_ctrl_id);
+
+static struct platform_driver qemu_virt_ctrl_driver = {
+	.probe = qemu_virt_ctrl_probe,
+	.driver = {
+		.name = "qemu-virt-ctrl",
+	},
+	.id_table = qemu_virt_ctrl_id,
+};
+module_platform_driver(qemu_virt_ctrl_driver);
+
+MODULE_AUTHOR("Kuan-Wei Chiu <visitorckw@gmail.com>");
+MODULE_DESCRIPTION("QEMU Virt Machine System Controller Driver");
+MODULE_LICENSE("GPL");