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, 68 insertions, 0 deletions

diff --git a/drivers/leds/trigger/ledtrig-panic.c b/drivers/leds/trigger/ledtrig-panic.c
new file mode 100644
index 000000000..1d49c1078
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-panic.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Kernel Panic LED Trigger
+ *
+ * Copyright 2016 Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
+ */
+
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <linux/panic_notifier.h>
+#include <linux/leds.h>
+#include "../leds.h"
+
+static struct led_trigger *trigger;
+
+/*
+ * This is called in a special context by the atomic panic
+ * notifier. This means the trigger can be changed without
+ * worrying about locking.
+ */
+static void led_trigger_set_panic(struct led_classdev *led_cdev)
+{
+	if (led_cdev->trigger)
+		list_del(&led_cdev->trig_list);
+	list_add_tail(&led_cdev->trig_list, &trigger->led_cdevs);
+
+	/* Avoid the delayed blink path */
+	led_cdev->blink_delay_on = 0;
+	led_cdev->blink_delay_off = 0;
+
+	led_cdev->trigger = trigger;
+}
+
+static int led_trigger_panic_notifier(struct notifier_block *nb,
+				      unsigned long code, void *unused)
+{
+	struct led_classdev *led_cdev;
+
+	list_for_each_entry(led_cdev, &leds_list, node)
+		if (led_cdev->flags & LED_PANIC_INDICATOR)
+			led_trigger_set_panic(led_cdev);
+	return NOTIFY_DONE;
+}
+
+static struct notifier_block led_trigger_panic_nb = {
+	.notifier_call = led_trigger_panic_notifier,
+};
+
+static long led_panic_blink(int state)
+{
+	led_trigger_event(trigger, state ? LED_FULL : LED_OFF);
+	return 0;
+}
+
+static int __init ledtrig_panic_init(void)
+{
+	led_trigger_register_simple("panic", &trigger);
+	if (!trigger)
+		return -ENOMEM;
+
+	atomic_notifier_chain_register(&panic_notifier_list,
+				       &led_trigger_panic_nb);
+
+	panic_blink = led_panic_blink;
+	return 0;
+}
+device_initcall(ledtrig_panic_init);