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, 217 insertions, 0 deletions

diff --git a/drivers/hwmon/g760a.c b/drivers/hwmon/g760a.c
new file mode 100644
index 000000000..e2166ee76
--- /dev/null
+++ b/drivers/hwmon/g760a.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * g760a - Driver for the Global Mixed-mode Technology Inc. G760A
+ *	   fan speed PWM controller chip
+ *
+ * Copyright (C) 2007  Herbert Valerio Riedel <hvr@gnu.org>
+ *
+ * Complete datasheet is available at GMT's website:
+ * http://www.gmt.com.tw/product/datasheet/EDS-760A.pdf
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/jiffies.h>
+#include <linux/i2c.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/err.h>
+#include <linux/mutex.h>
+#include <linux/sysfs.h>
+
+enum g760a_regs {
+	G760A_REG_SET_CNT = 0x00,
+	G760A_REG_ACT_CNT = 0x01,
+	G760A_REG_FAN_STA = 0x02
+};
+
+#define G760A_REG_FAN_STA_RPM_OFF 0x1 /* +/-20% off */
+#define G760A_REG_FAN_STA_RPM_LOW 0x2 /* below 1920rpm */
+
+/* register data is read (and cached) at most once per second */
+#define G760A_UPDATE_INTERVAL (HZ)
+
+struct g760a_data {
+	struct i2c_client *client;
+	struct mutex update_lock;
+
+	/* board specific parameters */
+	u32 clk; /* default 32kHz */
+	u16 fan_div; /* default P=2 */
+
+	/* g760a register cache */
+	unsigned int valid:1;
+	unsigned long last_updated; /* In jiffies */
+
+	u8 set_cnt; /* PWM (period) count number; 0xff stops fan */
+	u8 act_cnt; /*   formula: cnt = (CLK * 30)/(rpm * P) */
+	u8 fan_sta; /* bit 0: set when actual fan speed more than 20%
+		     *   outside requested fan speed
+		     * bit 1: set when fan speed below 1920 rpm
+		     */
+};
+
+#define G760A_DEFAULT_CLK 32768
+#define G760A_DEFAULT_FAN_DIV 2
+
+#define PWM_FROM_CNT(cnt)	(0xff-(cnt))
+#define PWM_TO_CNT(pwm)		(0xff-(pwm))
+
+static inline unsigned int rpm_from_cnt(u8 val, u32 clk, u16 div)
+{
+	return ((val == 0x00) ? 0 : ((clk*30)/(val*div)));
+}
+
+/* read/write wrappers */
+static int g760a_read_value(struct i2c_client *client, enum g760a_regs reg)
+{
+	return i2c_smbus_read_byte_data(client, reg);
+}
+
+static int g760a_write_value(struct i2c_client *client, enum g760a_regs reg,
+			     u16 value)
+{
+	return i2c_smbus_write_byte_data(client, reg, value);
+}
+
+/*
+ * sysfs attributes
+ */
+
+static struct g760a_data *g760a_update_client(struct device *dev)
+{
+	struct g760a_data *data = dev_get_drvdata(dev);
+	struct i2c_client *client = data->client;
+
+	mutex_lock(&data->update_lock);
+
+	if (time_after(jiffies, data->last_updated + G760A_UPDATE_INTERVAL)
+	    || !data->valid) {
+		dev_dbg(&client->dev, "Starting g760a update\n");
+
+		data->set_cnt = g760a_read_value(client, G760A_REG_SET_CNT);
+		data->act_cnt = g760a_read_value(client, G760A_REG_ACT_CNT);
+		data->fan_sta = g760a_read_value(client, G760A_REG_FAN_STA);
+
+		data->last_updated = jiffies;
+		data->valid = true;
+	}
+
+	mutex_unlock(&data->update_lock);
+
+	return data;
+}
+
+static ssize_t fan1_input_show(struct device *dev,
+			       struct device_attribute *da, char *buf)
+{
+	struct g760a_data *data = g760a_update_client(dev);
+	unsigned int rpm = 0;
+
+	mutex_lock(&data->update_lock);
+	if (!(data->fan_sta & G760A_REG_FAN_STA_RPM_LOW))
+		rpm = rpm_from_cnt(data->act_cnt, data->clk, data->fan_div);
+	mutex_unlock(&data->update_lock);
+
+	return sprintf(buf, "%d\n", rpm);
+}
+
+static ssize_t fan1_alarm_show(struct device *dev,
+			       struct device_attribute *da, char *buf)
+{
+	struct g760a_data *data = g760a_update_client(dev);
+
+	int fan_alarm = (data->fan_sta & G760A_REG_FAN_STA_RPM_OFF) ? 1 : 0;
+
+	return sprintf(buf, "%d\n", fan_alarm);
+}
+
+static ssize_t pwm1_show(struct device *dev, struct device_attribute *da,
+			 char *buf)
+{
+	struct g760a_data *data = g760a_update_client(dev);
+
+	return sprintf(buf, "%d\n", PWM_FROM_CNT(data->set_cnt));
+}
+
+static ssize_t pwm1_store(struct device *dev, struct device_attribute *da,
+			  const char *buf, size_t count)
+{
+	struct g760a_data *data = g760a_update_client(dev);
+	struct i2c_client *client = data->client;
+	unsigned long val;
+
+	if (kstrtoul(buf, 10, &val))
+		return -EINVAL;
+
+	mutex_lock(&data->update_lock);
+	data->set_cnt = PWM_TO_CNT(clamp_val(val, 0, 255));
+	g760a_write_value(client, G760A_REG_SET_CNT, data->set_cnt);
+	mutex_unlock(&data->update_lock);
+
+	return count;
+}
+
+static DEVICE_ATTR_RW(pwm1);
+static DEVICE_ATTR_RO(fan1_input);
+static DEVICE_ATTR_RO(fan1_alarm);
+
+static struct attribute *g760a_attrs[] = {
+	&dev_attr_pwm1.attr,
+	&dev_attr_fan1_input.attr,
+	&dev_attr_fan1_alarm.attr,
+	NULL
+};
+
+ATTRIBUTE_GROUPS(g760a);
+
+/*
+ * new-style driver model code
+ */
+
+static int g760a_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct g760a_data *data;
+	struct device *hwmon_dev;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_SMBUS_BYTE_DATA))
+		return -EIO;
+
+	data = devm_kzalloc(dev, sizeof(struct g760a_data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+	mutex_init(&data->update_lock);
+
+	/* setup default configuration for now */
+	data->fan_div = G760A_DEFAULT_FAN_DIV;
+	data->clk = G760A_DEFAULT_CLK;
+
+	hwmon_dev = devm_hwmon_device_register_with_groups(dev, client->name,
+							   data,
+							   g760a_groups);
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id g760a_id[] = {
+	{ .name = "g760a" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, g760a_id);
+
+static struct i2c_driver g760a_driver = {
+	.driver = {
+		.name	= "g760a",
+	},
+	.probe = g760a_probe,
+	.id_table = g760a_id,
+};
+
+module_i2c_driver(g760a_driver);
+
+MODULE_AUTHOR("Herbert Valerio Riedel <hvr@gnu.org>");
+MODULE_DESCRIPTION("GMT G760A driver");
+MODULE_LICENSE("GPL");