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, 59 insertions, 0 deletions

diff --git a/drivers/media/dvb-frontends/mt352.h b/drivers/media/dvb-frontends/mt352.h
new file mode 100644
index 000000000..acb1c3374
--- /dev/null
+++ b/drivers/media/dvb-frontends/mt352.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  Driver for Zarlink DVB-T MT352 demodulator
+ *
+ *  Written by Holger Waechtler <holger@qanu.de>
+ *	 and Daniel Mack <daniel@qanu.de>
+ *
+ *  AVerMedia AVerTV DVB-T 771 support by
+ *       Wolfram Joost <dbox2@frokaschwei.de>
+ *
+ *  Support for Samsung TDTC9251DH01C(M) tuner
+ *  Copyright (C) 2004 Antonio Mancuso <antonio.mancuso@digitaltelevision.it>
+ *                     Amauri  Celani  <acelani@essegi.net>
+ *
+ *  DVICO FusionHDTV DVB-T1 and DVICO FusionHDTV DVB-T Lite support by
+ *       Christopher Pascoe <c.pascoe@itee.uq.edu.au>
+ */
+
+#ifndef MT352_H
+#define MT352_H
+
+#include <linux/dvb/frontend.h>
+
+struct mt352_config
+{
+	/* the demodulator's i2c address */
+	u8 demod_address;
+
+	/* frequencies in kHz */
+	int adc_clock;  // default: 20480
+	int if2;        // default: 36166
+
+	/* set if no pll is connected to the secondary i2c bus */
+	int no_tuner;
+
+	/* Initialise the demodulator and PLL. Cannot be NULL */
+	int (*demod_init)(struct dvb_frontend* fe);
+};
+
+#if IS_REACHABLE(CONFIG_DVB_MT352)
+extern struct dvb_frontend* mt352_attach(const struct mt352_config* config,
+					 struct i2c_adapter* i2c);
+#else
+static inline struct dvb_frontend* mt352_attach(const struct mt352_config* config,
+					 struct i2c_adapter* i2c)
+{
+	printk(KERN_WARNING "%s: driver disabled by Kconfig\n", __func__);
+	return NULL;
+}
+#endif // CONFIG_DVB_MT352
+
+static inline int mt352_write(struct dvb_frontend *fe, const u8 buf[], int len) {
+	int r = 0;
+	if (fe->ops.write)
+		r = fe->ops.write(fe, buf, len);
+	return r;
+}
+
+#endif // MT352_H