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, 87 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/fakekey.c b/drivers/accessibility/speakup/fakekey.c
new file mode 100644
index 000000000..9c0b24038
--- /dev/null
+++ b/drivers/accessibility/speakup/fakekey.c
@@ -0,0 +1,87 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* fakekey.c
+ * Functions for simulating key presses.
+ *
+ * Copyright (C) 2010 the Speakup Team
+ */
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/preempt.h>
+#include <linux/percpu.h>
+#include <linux/input.h>
+
+#include "speakup.h"
+
+#define PRESSED 1
+#define RELEASED 0
+
+static DEFINE_PER_CPU(int, reporting_keystroke);
+
+static struct input_dev *virt_keyboard;
+
+int speakup_add_virtual_keyboard(void)
+{
+	int err;
+
+	virt_keyboard = input_allocate_device();
+
+	if (!virt_keyboard)
+		return -ENOMEM;
+
+	virt_keyboard->name = "Speakup";
+	virt_keyboard->id.bustype = BUS_VIRTUAL;
+	virt_keyboard->phys = "speakup/input0";
+	virt_keyboard->dev.parent = NULL;
+
+	__set_bit(EV_KEY, virt_keyboard->evbit);
+	__set_bit(KEY_DOWN, virt_keyboard->keybit);
+
+	err = input_register_device(virt_keyboard);
+	if (err) {
+		input_free_device(virt_keyboard);
+		virt_keyboard = NULL;
+	}
+
+	return err;
+}
+
+void speakup_remove_virtual_keyboard(void)
+{
+	if (virt_keyboard) {
+		input_unregister_device(virt_keyboard);
+		virt_keyboard = NULL;
+	}
+}
+
+/*
+ * Send a simulated down-arrow to the application.
+ */
+void speakup_fake_down_arrow(void)
+{
+	unsigned long flags;
+
+	/* disable keyboard interrupts */
+	local_irq_save(flags);
+	/* don't change CPU */
+	preempt_disable();
+
+	__this_cpu_write(reporting_keystroke, true);
+	input_report_key(virt_keyboard, KEY_DOWN, PRESSED);
+	input_report_key(virt_keyboard, KEY_DOWN, RELEASED);
+	input_sync(virt_keyboard);
+	__this_cpu_write(reporting_keystroke, false);
+
+	/* re-enable preemption */
+	preempt_enable();
+	/* re-enable keyboard interrupts */
+	local_irq_restore(flags);
+}
+
+/*
+ * Are we handling a simulated key press on the current CPU?
+ * Returns a boolean.
+ */
+bool speakup_fake_key_pressed(void)
+{
+	return this_cpu_read(reporting_keystroke);
+}