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, 159 insertions, 0 deletions

diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
new file mode 100644
index 000000000..7d02470f1
--- /dev/null
+++ b/drivers/video/console/dummycon.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/drivers/video/dummycon.c -- A dummy console driver
+ *
+ *  To be used if there's no other console driver (e.g. for plain VGA text)
+ *  available, usually until fbcon takes console over.
+ */
+
+#include <linux/types.h>
+#include <linux/kdev_t.h>
+#include <linux/console.h>
+#include <linux/vt_kern.h>
+#include <linux/screen_info.h>
+#include <linux/init.h>
+#include <linux/module.h>
+
+/*
+ *  Dummy console driver
+ */
+
+#if defined(CONFIG_ARCH_FOOTBRIDGE) && defined(CONFIG_VGA_CONSOLE)
+#include <asm/vga.h>
+#define DUMMY_COLUMNS	vgacon_screen_info.orig_video_cols
+#define DUMMY_ROWS	vgacon_screen_info.orig_video_lines
+#else
+/* set by Kconfig. Use 80x25 for 640x480 and 160x64 for 1280x1024 */
+#define DUMMY_COLUMNS	CONFIG_DUMMY_CONSOLE_COLUMNS
+#define DUMMY_ROWS	CONFIG_DUMMY_CONSOLE_ROWS
+#endif
+
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+/* These are both protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_output_nh);
+static bool dummycon_putc_called;
+
+void dummycon_register_output_notifier(struct notifier_block *nb)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	raw_notifier_chain_register(&dummycon_output_nh, nb);
+
+	if (dummycon_putc_called)
+		nb->notifier_call(nb, 0, NULL);
+}
+
+void dummycon_unregister_output_notifier(struct notifier_block *nb)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	raw_notifier_chain_unregister(&dummycon_output_nh, nb);
+}
+
+static void dummycon_putc(struct vc_data *vc, u16 c, unsigned int y,
+                          unsigned int x)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	dummycon_putc_called = true;
+	raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
+}
+
+static void dummycon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
+			   unsigned int ypos, unsigned int xpos)
+{
+	unsigned int i;
+
+	if (!dummycon_putc_called) {
+		/* Ignore erases */
+		for (i = 0 ; i < count; i++) {
+			if (s[i] != vc->vc_video_erase_char)
+				break;
+		}
+		if (i == count)
+			return;
+
+		dummycon_putc_called = true;
+	}
+
+	raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
+}
+
+static bool dummycon_blank(struct vc_data *vc, enum vesa_blank_mode blank,
+			   bool mode_switch)
+{
+	/* Redraw, so that we get putc(s) for output done while blanked */
+	return true;
+}
+
+static bool dummycon_switch(struct vc_data *vc)
+{
+	/*
+	 * Redraw, so that we get putc(s) for output done while switched
+	 * away. Informs deferred consoles to take over the display.
+	 */
+	return true;
+}
+#else
+static void dummycon_putc(struct vc_data *vc, u16 c, unsigned int y,
+			  unsigned int x) { }
+static void dummycon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
+			   unsigned int ypos, unsigned int xpos) { }
+static bool dummycon_blank(struct vc_data *vc, enum vesa_blank_mode blank,
+			   bool mode_switch)
+{
+	return false;
+}
+static bool dummycon_switch(struct vc_data *vc)
+{
+	return false;
+}
+#endif
+
+static const char *dummycon_startup(void)
+{
+    return "dummy device";
+}
+
+static void dummycon_init(struct vc_data *vc, bool init)
+{
+    vc->vc_can_do_color = 1;
+    if (init) {
+	vc->vc_cols = DUMMY_COLUMNS;
+	vc->vc_rows = DUMMY_ROWS;
+    } else
+	vc_resize(vc, DUMMY_COLUMNS, DUMMY_ROWS);
+}
+
+static void dummycon_deinit(struct vc_data *vc) { }
+static void dummycon_clear(struct vc_data *vc, unsigned int sy, unsigned int sx,
+			   unsigned int width) { }
+static void dummycon_cursor(struct vc_data *vc, bool enable) { }
+
+static bool dummycon_scroll(struct vc_data *vc, unsigned int top,
+			    unsigned int bottom, enum con_scroll dir,
+			    unsigned int lines)
+{
+	return false;
+}
+
+/*
+ *  The console `switch' structure for the dummy console
+ *
+ *  Most of the operations are dummies.
+ */
+
+const struct consw dummy_con = {
+	.owner =		THIS_MODULE,
+	.con_startup =	dummycon_startup,
+	.con_init =		dummycon_init,
+	.con_deinit =	dummycon_deinit,
+	.con_clear =	dummycon_clear,
+	.con_putc =		dummycon_putc,
+	.con_putcs =	dummycon_putcs,
+	.con_cursor =	dummycon_cursor,
+	.con_scroll =	dummycon_scroll,
+	.con_switch =	dummycon_switch,
+	.con_blank =	dummycon_blank,
+};
+EXPORT_SYMBOL_GPL(dummy_con);