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, 184 insertions, 0 deletions

diff --git a/drivers/hwmon/ltc4260.c b/drivers/hwmon/ltc4260.c
new file mode 100644
index 000000000..37a85125d
--- /dev/null
+++ b/drivers/hwmon/ltc4260.c
@@ -0,0 +1,184 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Driver for Linear Technology LTC4260 I2C Positive Voltage Hot Swap Controller
+ *
+ * Copyright (c) 2014 Guenter Roeck
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/err.h>
+#include <linux/slab.h>
+#include <linux/i2c.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/jiffies.h>
+#include <linux/regmap.h>
+
+/* chip registers */
+#define LTC4260_CONTROL	0x00
+#define LTC4260_ALERT	0x01
+#define LTC4260_STATUS	0x02
+#define LTC4260_FAULT	0x03
+#define LTC4260_SENSE	0x04
+#define LTC4260_SOURCE	0x05
+#define LTC4260_ADIN	0x06
+
+/*
+ * Fault register bits
+ */
+#define FAULT_OV	(1 << 0)
+#define FAULT_UV	(1 << 1)
+#define FAULT_OC	(1 << 2)
+#define FAULT_POWER_BAD	(1 << 3)
+#define FAULT_FET_SHORT	(1 << 5)
+
+/* Return the voltage from the given register in mV or mA */
+static int ltc4260_get_value(struct device *dev, u8 reg)
+{
+	struct regmap *regmap = dev_get_drvdata(dev);
+	unsigned int val;
+	int ret;
+
+	ret = regmap_read(regmap, reg, &val);
+	if (ret < 0)
+		return ret;
+
+	switch (reg) {
+	case LTC4260_ADIN:
+		/* 10 mV resolution. Convert to mV. */
+		val = val * 10;
+		break;
+	case LTC4260_SOURCE:
+		/* 400 mV resolution. Convert to mV. */
+		val = val * 400;
+		break;
+	case LTC4260_SENSE:
+		/*
+		 * 300 uV resolution. Convert to current as measured with
+		 * an 1 mOhm sense resistor, in mA. If a different sense
+		 * resistor is installed, calculate the actual current by
+		 * dividing the reported current by the sense resistor value
+		 * in mOhm.
+		 */
+		val = val * 300;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return val;
+}
+
+static ssize_t ltc4260_value_show(struct device *dev,
+				  struct device_attribute *da, char *buf)
+{
+	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
+	int value;
+
+	value = ltc4260_get_value(dev, attr->index);
+	if (value < 0)
+		return value;
+	return sysfs_emit(buf, "%d\n", value);
+}
+
+static ssize_t ltc4260_bool_show(struct device *dev,
+				 struct device_attribute *da, char *buf)
+{
+	struct sensor_device_attribute *attr = to_sensor_dev_attr(da);
+	struct regmap *regmap = dev_get_drvdata(dev);
+	unsigned int fault;
+	int ret;
+
+	ret = regmap_read(regmap, LTC4260_FAULT, &fault);
+	if (ret < 0)
+		return ret;
+
+	fault &= attr->index;
+	if (fault)		/* Clear reported faults in chip register */
+		regmap_update_bits(regmap, LTC4260_FAULT, attr->index, 0);
+
+	return sysfs_emit(buf, "%d\n", !!fault);
+}
+
+/* Voltages */
+static SENSOR_DEVICE_ATTR_RO(in1_input, ltc4260_value, LTC4260_SOURCE);
+static SENSOR_DEVICE_ATTR_RO(in2_input, ltc4260_value, LTC4260_ADIN);
+
+/*
+ * Voltage alarms
+ * UV/OV faults are associated with the input voltage, and the POWER BAD and
+ * FET SHORT faults are associated with the output voltage.
+ */
+static SENSOR_DEVICE_ATTR_RO(in1_min_alarm, ltc4260_bool, FAULT_UV);
+static SENSOR_DEVICE_ATTR_RO(in1_max_alarm, ltc4260_bool, FAULT_OV);
+static SENSOR_DEVICE_ATTR_RO(in2_alarm, ltc4260_bool,
+			     FAULT_POWER_BAD | FAULT_FET_SHORT);
+
+/* Current (via sense resistor) */
+static SENSOR_DEVICE_ATTR_RO(curr1_input, ltc4260_value, LTC4260_SENSE);
+
+/* Overcurrent alarm */
+static SENSOR_DEVICE_ATTR_RO(curr1_max_alarm, ltc4260_bool, FAULT_OC);
+
+static struct attribute *ltc4260_attrs[] = {
+	&sensor_dev_attr_in1_input.dev_attr.attr,
+	&sensor_dev_attr_in1_min_alarm.dev_attr.attr,
+	&sensor_dev_attr_in1_max_alarm.dev_attr.attr,
+	&sensor_dev_attr_in2_input.dev_attr.attr,
+	&sensor_dev_attr_in2_alarm.dev_attr.attr,
+
+	&sensor_dev_attr_curr1_input.dev_attr.attr,
+	&sensor_dev_attr_curr1_max_alarm.dev_attr.attr,
+
+	NULL,
+};
+ATTRIBUTE_GROUPS(ltc4260);
+
+static const struct regmap_config ltc4260_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = LTC4260_ADIN,
+};
+
+static int ltc4260_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct device *hwmon_dev;
+	struct regmap *regmap;
+
+	regmap = devm_regmap_init_i2c(client, &ltc4260_regmap_config);
+	if (IS_ERR(regmap)) {
+		dev_err(dev, "failed to allocate register map\n");
+		return PTR_ERR(regmap);
+	}
+
+	/* Clear faults */
+	regmap_write(regmap, LTC4260_FAULT, 0x00);
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
+							   regmap,
+							   ltc4260_groups);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id ltc4260_id[] = {
+	{ .name = "ltc4260" },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(i2c, ltc4260_id);
+
+static struct i2c_driver ltc4260_driver = {
+	.driver = {
+		   .name = "ltc4260",
+		   },
+	.probe = ltc4260_probe,
+	.id_table = ltc4260_id,
+};
+
+module_i2c_driver(ltc4260_driver);
+
+MODULE_AUTHOR("Guenter Roeck <linux@roeck-us.net>");
+MODULE_DESCRIPTION("LTC4260 driver");
+MODULE_LICENSE("GPL");