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, 160 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-max6916.c b/drivers/rtc/rtc-max6916.c
new file mode 100644
index 000000000..e72e768ab
--- /dev/null
+++ b/drivers/rtc/rtc-max6916.c
@@ -0,0 +1,160 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* rtc-max6916.c
+ *
+ * Driver for MAXIM  max6916 Low Current, SPI Compatible
+ * Real Time Clock
+ *
+ * Author : Venkat Prashanth B U <venkat.prashanth2498@gmail.com>
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+
+/* Registers in max6916 rtc */
+
+#define MAX6916_SECONDS_REG	0x01
+#define MAX6916_MINUTES_REG	0x02
+#define MAX6916_HOURS_REG	0x03
+#define MAX6916_DATE_REG	0x04
+#define MAX6916_MONTH_REG	0x05
+#define MAX6916_DAY_REG	0x06
+#define MAX6916_YEAR_REG	0x07
+#define MAX6916_CONTROL_REG	0x08
+#define MAX6916_STATUS_REG	0x0C
+#define MAX6916_CLOCK_BURST	0x3F
+
+static int max6916_read_reg(struct device *dev, unsigned char address,
+			    unsigned char *data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+
+	*data = address | 0x80;
+
+	return spi_write_then_read(spi, data, 1, data, 1);
+}
+
+static int max6916_write_reg(struct device *dev, unsigned char address,
+			     unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	buf[0] = address & 0x7F;
+	buf[1] = data;
+
+	return spi_write_then_read(spi, buf, 2, NULL, 0);
+}
+
+static int max6916_read_time(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	int err;
+	unsigned char buf[8];
+
+	buf[0] = MAX6916_CLOCK_BURST | 0x80;
+
+	err = spi_write_then_read(spi, buf, 1, buf, 8);
+
+	if (err)
+		return err;
+
+	dt->tm_sec = bcd2bin(buf[0]);
+	dt->tm_min = bcd2bin(buf[1]);
+	dt->tm_hour = bcd2bin(buf[2] & 0x3F);
+	dt->tm_mday = bcd2bin(buf[3]);
+	dt->tm_mon = bcd2bin(buf[4]) - 1;
+	dt->tm_wday = bcd2bin(buf[5]) - 1;
+	dt->tm_year = bcd2bin(buf[6]) + 100;
+
+	return 0;
+}
+
+static int max6916_set_time(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[9];
+
+	if (dt->tm_year < 100 || dt->tm_year > 199) {
+		dev_err(&spi->dev, "Year must be between 2000 and 2099. It's %d.\n",
+			dt->tm_year + 1900);
+		return -EINVAL;
+	}
+
+	buf[0] = MAX6916_CLOCK_BURST & 0x7F;
+	buf[1] = bin2bcd(dt->tm_sec);
+	buf[2] = bin2bcd(dt->tm_min);
+	buf[3] = (bin2bcd(dt->tm_hour) & 0X3F);
+	buf[4] = bin2bcd(dt->tm_mday);
+	buf[5] = bin2bcd(dt->tm_mon + 1);
+	buf[6] = bin2bcd(dt->tm_wday + 1);
+	buf[7] = bin2bcd(dt->tm_year % 100);
+	buf[8] = bin2bcd(0x00);
+
+	/* write the rtc settings */
+	return spi_write_then_read(spi, buf, 9, NULL, 0);
+}
+
+static const struct rtc_class_ops max6916_rtc_ops = {
+	.read_time = max6916_read_time,
+	.set_time = max6916_set_time,
+};
+
+static int max6916_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	unsigned char data;
+	int res;
+
+	/* spi setup with max6916 in mode 3 and bits per word as 8 */
+	spi->mode = SPI_MODE_3;
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	/* RTC Settings */
+	res = max6916_read_reg(&spi->dev, MAX6916_SECONDS_REG, &data);
+	if (res)
+		return res;
+
+	/* Disable the write protect of rtc */
+	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
+	data = data & ~(1 << 7);
+	max6916_write_reg(&spi->dev, MAX6916_CONTROL_REG, data);
+
+	/*Enable oscillator,disable oscillator stop flag, glitch filter*/
+	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
+	data = data & 0x1B;
+	max6916_write_reg(&spi->dev, MAX6916_STATUS_REG, data);
+
+	/* display the settings */
+	max6916_read_reg(&spi->dev, MAX6916_CONTROL_REG, &data);
+	dev_info(&spi->dev, "MAX6916 RTC CTRL Reg = 0x%02x\n", data);
+
+	max6916_read_reg(&spi->dev, MAX6916_STATUS_REG, &data);
+	dev_info(&spi->dev, "MAX6916 RTC Status Reg = 0x%02x\n", data);
+
+	rtc = devm_rtc_device_register(&spi->dev, "max6916",
+				       &max6916_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	spi_set_drvdata(spi, rtc);
+
+	return 0;
+}
+
+static struct spi_driver max6916_driver = {
+	.driver = {
+		.name = "max6916",
+	},
+	.probe = max6916_probe,
+};
+module_spi_driver(max6916_driver);
+
+MODULE_DESCRIPTION("MAX6916 SPI RTC DRIVER");
+MODULE_AUTHOR("Venkat Prashanth B U <venkat.prashanth2498@gmail.com>");
+MODULE_LICENSE("GPL v2");