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, 41 insertions, 0 deletions

diff --git a/drivers/hwmon/lm75.h b/drivers/hwmon/lm75.h
new file mode 100644
index 000000000..b803ada5e
--- /dev/null
+++ b/drivers/hwmon/lm75.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * lm75.h - Part of lm_sensors, Linux kernel modules for hardware monitoring
+ * Copyright (c) 2003 Mark M. Hoffman <mhoffman@lightlink.com>
+ */
+
+/*
+ * This file contains common code for encoding/decoding LM75 type
+ * temperature readings, which are emulated by many of the chips
+ * we support.  As the user is unlikely to load more than one driver
+ * which contains this code, we don't worry about the wasted space.
+ */
+
+#include <linux/minmax.h>
+#include <linux/types.h>
+
+/* straight from the datasheet */
+#define LM75_TEMP_MIN (-55000)
+#define LM75_TEMP_MAX 125000
+#define LM75_SHUTDOWN 0x01
+
+/*
+ * TEMP: 0.001C/bit (-55C to +125C)
+ * REG: (0.5C/bit, two's complement) << 7
+ */
+static inline u16 LM75_TEMP_TO_REG(long temp)
+{
+	int ntemp = clamp_val(temp, LM75_TEMP_MIN, LM75_TEMP_MAX);
+
+	ntemp += (ntemp < 0 ? -250 : 250);
+	return (u16)((ntemp / 500) << 7);
+}
+
+static inline int LM75_TEMP_FROM_REG(u16 reg)
+{
+	/*
+	 * use integer division instead of equivalent right shift to
+	 * guarantee arithmetic shift and preserve the sign
+	 */
+	return ((s16)reg / 128) * 500;
+}