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, 154 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-max6902.c b/drivers/rtc/rtc-max6902.c
new file mode 100644
index 000000000..daaeb6fb6
--- /dev/null
+++ b/drivers/rtc/rtc-max6902.c
@@ -0,0 +1,154 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* drivers/rtc/rtc-max6902.c
+ *
+ * Copyright (C) 2006 8D Technologies inc.
+ * Copyright (C) 2004 Compulab Ltd.
+ *
+ * Driver for MAX6902 spi RTC
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/init.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+
+#define MAX6902_REG_SECONDS		0x01
+#define MAX6902_REG_MINUTES		0x03
+#define MAX6902_REG_HOURS		0x05
+#define MAX6902_REG_DATE		0x07
+#define MAX6902_REG_MONTH		0x09
+#define MAX6902_REG_DAY			0x0B
+#define MAX6902_REG_YEAR		0x0D
+#define MAX6902_REG_CONTROL		0x0F
+#define MAX6902_REG_CENTURY		0x13
+
+static int max6902_set_reg(struct device *dev, unsigned char address,
+				unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	/* MSB must be '0' to write */
+	buf[0] = address & 0x7f;
+	buf[1] = data;
+
+	return spi_write_then_read(spi, buf, 2, NULL, 0);
+}
+
+static int max6902_get_reg(struct device *dev, unsigned char address,
+				unsigned char *data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+
+	/* Set MSB to indicate read */
+	*data = address | 0x80;
+
+	return spi_write_then_read(spi, data, 1, data, 1);
+}
+
+static int max6902_read_time(struct device *dev, struct rtc_time *dt)
+{
+	int err, century;
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[8];
+
+	buf[0] = 0xbf;	/* Burst read */
+
+	err = spi_write_then_read(spi, buf, 1, buf, 8);
+	if (err != 0)
+		return err;
+
+	/* The chip sends data in this order:
+	 * Seconds, Minutes, Hours, Date, Month, Day, Year */
+	dt->tm_sec	= bcd2bin(buf[0]);
+	dt->tm_min	= bcd2bin(buf[1]);
+	dt->tm_hour	= bcd2bin(buf[2]);
+	dt->tm_mday	= bcd2bin(buf[3]);
+	dt->tm_mon	= bcd2bin(buf[4]) - 1;
+	dt->tm_wday	= bcd2bin(buf[5]);
+	dt->tm_year	= bcd2bin(buf[6]);
+
+	/* Read century */
+	err = max6902_get_reg(dev, MAX6902_REG_CENTURY, &buf[0]);
+	if (err != 0)
+		return err;
+
+	century = bcd2bin(buf[0]) * 100;
+
+	dt->tm_year += century;
+	dt->tm_year -= 1900;
+
+	return 0;
+}
+
+static int max6902_set_time(struct device *dev, struct rtc_time *dt)
+{
+	dt->tm_year = dt->tm_year + 1900;
+
+	/* Remove write protection */
+	max6902_set_reg(dev, MAX6902_REG_CONTROL, 0);
+
+	max6902_set_reg(dev, MAX6902_REG_SECONDS, bin2bcd(dt->tm_sec));
+	max6902_set_reg(dev, MAX6902_REG_MINUTES, bin2bcd(dt->tm_min));
+	max6902_set_reg(dev, MAX6902_REG_HOURS, bin2bcd(dt->tm_hour));
+
+	max6902_set_reg(dev, MAX6902_REG_DATE, bin2bcd(dt->tm_mday));
+	max6902_set_reg(dev, MAX6902_REG_MONTH, bin2bcd(dt->tm_mon + 1));
+	max6902_set_reg(dev, MAX6902_REG_DAY, bin2bcd(dt->tm_wday));
+	max6902_set_reg(dev, MAX6902_REG_YEAR, bin2bcd(dt->tm_year % 100));
+	max6902_set_reg(dev, MAX6902_REG_CENTURY, bin2bcd(dt->tm_year / 100));
+
+	/* Compulab used a delay here. However, the datasheet
+	 * does not mention a delay being required anywhere... */
+	/* delay(2000); */
+
+	/* Write protect */
+	max6902_set_reg(dev, MAX6902_REG_CONTROL, 0x80);
+
+	return 0;
+}
+
+static const struct rtc_class_ops max6902_rtc_ops = {
+	.read_time	= max6902_read_time,
+	.set_time	= max6902_set_time,
+};
+
+static int max6902_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	unsigned char tmp;
+	int res;
+
+	spi->mode = SPI_MODE_3;
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	res = max6902_get_reg(&spi->dev, MAX6902_REG_SECONDS, &tmp);
+	if (res != 0)
+		return res;
+
+	rtc = devm_rtc_device_register(&spi->dev, "max6902",
+				&max6902_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	spi_set_drvdata(spi, rtc);
+	return 0;
+}
+
+static struct spi_driver max6902_driver = {
+	.driver = {
+		.name	= "rtc-max6902",
+	},
+	.probe	= max6902_probe,
+};
+
+module_spi_driver(max6902_driver);
+
+MODULE_DESCRIPTION("max6902 spi RTC driver");
+MODULE_AUTHOR("Raphael Assenat");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:rtc-max6902");