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, 92 insertions, 0 deletions

diff --git a/drivers/auxdisplay/line-display.h b/drivers/auxdisplay/line-display.h
new file mode 100644
index 000000000..36853b639
--- /dev/null
+++ b/drivers/auxdisplay/line-display.h
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Character line display core support
+ *
+ * Copyright (C) 2016 Imagination Technologies
+ * Author: Paul Burton <paul.burton@mips.com>
+ *
+ * Copyright (C) 2021 Glider bv
+ * Copyright (C) 2025 Jean-François Lessard
+ */
+
+#ifndef _LINEDISP_H
+#define _LINEDISP_H
+
+#include <linux/device.h>
+#include <linux/timer_types.h>
+
+#include <linux/map_to_7segment.h>
+#include <linux/map_to_14segment.h>
+
+struct linedisp;
+
+/**
+ * enum linedisp_map_type - type of the character mapping
+ * @LINEDISP_MAP_SEG7: Map characters to 7 segment display
+ * @LINEDISP_MAP_SEG14: Map characters to 14 segment display
+ */
+enum linedisp_map_type {
+	LINEDISP_MAP_SEG7,
+	LINEDISP_MAP_SEG14,
+};
+
+/**
+ * struct linedisp_map - character mapping
+ * @type: type of the character mapping
+ * @map: conversion character mapping
+ * @size: size of the @map
+ */
+struct linedisp_map {
+	enum linedisp_map_type type;
+	union {
+		struct seg7_conversion_map seg7;
+		struct seg14_conversion_map seg14;
+	} map;
+	unsigned int size;
+};
+
+/**
+ * struct linedisp_ops - character line display operations
+ * @get_map_type: Function called to get the character mapping, if required
+ * @update: Function called to update the display. This must not sleep!
+ */
+struct linedisp_ops {
+	int (*get_map_type)(struct linedisp *linedisp);
+	void (*update)(struct linedisp *linedisp);
+};
+
+/**
+ * struct linedisp - character line display private data structure
+ * @dev: the line display device
+ * @timer: timer used to implement scrolling
+ * @ops: character line display operations
+ * @buf: pointer to the buffer for the string currently displayed
+ * @message: the full message to display or scroll on the display
+ * @num_chars: the number of characters that can be displayed
+ * @message_len: the length of the @message string
+ * @scroll_pos: index of the first character of @message currently displayed
+ * @scroll_rate: scroll interval in jiffies
+ * @id: instance id of this display
+ */
+struct linedisp {
+	struct device dev;
+	struct timer_list timer;
+	const struct linedisp_ops *ops;
+	struct linedisp_map *map;
+	char *buf;
+	char *message;
+	unsigned int num_chars;
+	unsigned int message_len;
+	unsigned int scroll_pos;
+	unsigned int scroll_rate;
+	unsigned int id;
+};
+
+int linedisp_attach(struct linedisp *linedisp, struct device *dev,
+		    unsigned int num_chars, const struct linedisp_ops *ops);
+void linedisp_detach(struct device *dev);
+int linedisp_register(struct linedisp *linedisp, struct device *parent,
+		      unsigned int num_chars, const struct linedisp_ops *ops);
+void linedisp_unregister(struct linedisp *linedisp);
+
+#endif /* LINEDISP_H */