[PATCH v2 0/2] hwmon: (dell-smm) Improve ioctl handler

[PATCH v2 0/2] hwmon: (dell-smm) Improve ioctl handler

[Armin Wolf]

This patch series improves the ioctl handler in dell_smm_hwmon.
The first patch is simplifying the ioctl handler by removing
an unnecessary switch case, while the second patch is unifying
both i8k_ioctl() and i8k_ioctl_unlocked(), resulting in better
performance since i8k_mutex is only acquired when needed
(during fan status change) instead of being acquired for
every ioctl call.

Tested on a Dell Inspiron 3505.

changes in v2:
- simplify logic between mutex_lock()/_unlock()
- replace hardcoded values with sizeof statements

Armin Wolf (2):
  hwmon: (dell-smm) Simplify ioctl handler
  hwmon: (dell-smm) Unify i8k_ioctl() and i8k_ioctl_unlocked()

 drivers/hwmon/dell-smm-hwmon.c | 58 +++++++++++-----------------------
 1 file changed, 18 insertions(+), 40 deletions(-)

--
2.30.2

[PATCH v2 1/2] hwmon: (dell-smm) Simplify ioctl handler

[Armin Wolf]

The second switch-case has no real purpose:

- for I8K_BIOS_VERSION, val does not represent a return value,
  making the check for error values unnecessary.
- for I8K_MACHINE_ID, val remains zero, so the error check is
  unnecessary too.

Remove the switch-case and move the calls to copy_to_user()
into the first switch-case for I8K_BIOS_VERSION/_MACHINE_ID.
Omit buff[] since data->bios_machineid already contains the string
with the necessary zero padding through devm_kzalloc().

Tested on a Dell Inspiron 3505.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
---
 drivers/hwmon/dell-smm-hwmon.c | 30 +++++++++---------------------
 1 file changed, 9 insertions(+), 21 deletions(-)

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index 5596c211f38d..186d40938036 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -454,7 +454,6 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
 {
 	int val = 0;
 	int speed, err;
-	unsigned char buff[16];
 	int __user *argp = (int __user *)arg;

 	if (!argp)
@@ -468,15 +467,19 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd

 		val = (data->bios_version[0] << 16) |
 				(data->bios_version[1] << 8) | data->bios_version[2];
-		break;

+		if (copy_to_user(argp, &val, sizeof(val)))
+			return -EFAULT;
+
+		return 0;
 	case I8K_MACHINE_ID:
 		if (restricted && !capable(CAP_SYS_ADMIN))
 			return -EPERM;

-		strscpy_pad(buff, data->bios_machineid, sizeof(buff));
-		break;
+		if (copy_to_user(argp, data->bios_machineid, sizeof(data->bios_machineid)))
+			return -EFAULT;

+		return 0;
 	case I8K_FN_STATUS:
 		val = i8k_get_fn_status();
 		break;
@@ -527,23 +530,8 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
 	if (val < 0)
 		return val;

-	switch (cmd) {
-	case I8K_BIOS_VERSION:
-		if (copy_to_user(argp, &val, 4))
-			return -EFAULT;
-
-		break;
-	case I8K_MACHINE_ID:
-		if (copy_to_user(argp, buff, 16))
-			return -EFAULT;
-
-		break;
-	default:
-		if (copy_to_user(argp, &val, sizeof(int)))
-			return -EFAULT;
-
-		break;
-	}
+	if (copy_to_user(argp, &val, sizeof(int)))
+		return -EFAULT;

 	return 0;
 }
--
2.30.2

Re: [PATCH v2 1/2] hwmon: (dell-smm) Simplify ioctl handler

[Pali Rohár]

On Saturday 11 December 2021 16:54:21 Armin Wolf wrote:
> The second switch-case has no real purpose:
> 
> - for I8K_BIOS_VERSION, val does not represent a return value,
>   making the check for error values unnecessary.
> - for I8K_MACHINE_ID, val remains zero, so the error check is
>   unnecessary too.
> 
> Remove the switch-case and move the calls to copy_to_user()
> into the first switch-case for I8K_BIOS_VERSION/_MACHINE_ID.
> Omit buff[] since data->bios_machineid already contains the string
> with the necessary zero padding through devm_kzalloc().
> 
> Tested on a Dell Inspiron 3505.
> 
> Signed-off-by: Armin Wolf <W_Armin@gmx.de>

Reviewed-by: Pali Rohár <pali@kernel.org>

> ---
>  drivers/hwmon/dell-smm-hwmon.c | 30 +++++++++---------------------
>  1 file changed, 9 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index 5596c211f38d..186d40938036 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -454,7 +454,6 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
>  {
>  	int val = 0;
>  	int speed, err;
> -	unsigned char buff[16];
>  	int __user *argp = (int __user *)arg;
> 
>  	if (!argp)
> @@ -468,15 +467,19 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
> 
>  		val = (data->bios_version[0] << 16) |
>  				(data->bios_version[1] << 8) | data->bios_version[2];
> -		break;
> 
> +		if (copy_to_user(argp, &val, sizeof(val)))
> +			return -EFAULT;
> +
> +		return 0;
>  	case I8K_MACHINE_ID:
>  		if (restricted && !capable(CAP_SYS_ADMIN))
>  			return -EPERM;
> 
> -		strscpy_pad(buff, data->bios_machineid, sizeof(buff));
> -		break;
> +		if (copy_to_user(argp, data->bios_machineid, sizeof(data->bios_machineid)))
> +			return -EFAULT;
> 
> +		return 0;
>  	case I8K_FN_STATUS:
>  		val = i8k_get_fn_status();
>  		break;
> @@ -527,23 +530,8 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
>  	if (val < 0)
>  		return val;
> 
> -	switch (cmd) {
> -	case I8K_BIOS_VERSION:
> -		if (copy_to_user(argp, &val, 4))
> -			return -EFAULT;
> -
> -		break;
> -	case I8K_MACHINE_ID:
> -		if (copy_to_user(argp, buff, 16))
> -			return -EFAULT;
> -
> -		break;
> -	default:
> -		if (copy_to_user(argp, &val, sizeof(int)))
> -			return -EFAULT;
> -
> -		break;
> -	}
> +	if (copy_to_user(argp, &val, sizeof(int)))
> +		return -EFAULT;
> 
>  	return 0;
>  }
> --
> 2.30.2
> 

Re: [PATCH v2 1/2] hwmon: (dell-smm) Simplify ioctl handler

[Guenter Roeck]

On Sat, Dec 11, 2021 at 04:54:21PM +0100, Armin Wolf wrote:
> The second switch-case has no real purpose:
> 
> - for I8K_BIOS_VERSION, val does not represent a return value,
>   making the check for error values unnecessary.
> - for I8K_MACHINE_ID, val remains zero, so the error check is
>   unnecessary too.
> 
> Remove the switch-case and move the calls to copy_to_user()
> into the first switch-case for I8K_BIOS_VERSION/_MACHINE_ID.
> Omit buff[] since data->bios_machineid already contains the string
> with the necessary zero padding through devm_kzalloc().
> 
> Tested on a Dell Inspiron 3505.
> 
> Signed-off-by: Armin Wolf <W_Armin@gmx.de>
> Reviewed-by: Pali Rohár <pali@kernel.org>

Series applied.

Thanks,
Guenter

> ---
>  drivers/hwmon/dell-smm-hwmon.c | 30 +++++++++---------------------
>  1 file changed, 9 insertions(+), 21 deletions(-)
> 
> --
> 2.30.2
> 
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index 5596c211f38d..186d40938036 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -454,7 +454,6 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
>  {
>  	int val = 0;
>  	int speed, err;
> -	unsigned char buff[16];
>  	int __user *argp = (int __user *)arg;
> 
>  	if (!argp)
> @@ -468,15 +467,19 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
> 
>  		val = (data->bios_version[0] << 16) |
>  				(data->bios_version[1] << 8) | data->bios_version[2];
> -		break;
> 
> +		if (copy_to_user(argp, &val, sizeof(val)))
> +			return -EFAULT;
> +
> +		return 0;
>  	case I8K_MACHINE_ID:
>  		if (restricted && !capable(CAP_SYS_ADMIN))
>  			return -EPERM;
> 
> -		strscpy_pad(buff, data->bios_machineid, sizeof(buff));
> -		break;
> +		if (copy_to_user(argp, data->bios_machineid, sizeof(data->bios_machineid)))
> +			return -EFAULT;
> 
> +		return 0;
>  	case I8K_FN_STATUS:
>  		val = i8k_get_fn_status();
>  		break;
> @@ -527,23 +530,8 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
>  	if (val < 0)
>  		return val;
> 
> -	switch (cmd) {
> -	case I8K_BIOS_VERSION:
> -		if (copy_to_user(argp, &val, 4))
> -			return -EFAULT;
> -
> -		break;
> -	case I8K_MACHINE_ID:
> -		if (copy_to_user(argp, buff, 16))
> -			return -EFAULT;
> -
> -		break;
> -	default:
> -		if (copy_to_user(argp, &val, sizeof(int)))
> -			return -EFAULT;
> -
> -		break;
> -	}
> +	if (copy_to_user(argp, &val, sizeof(int)))
> +		return -EFAULT;
> 
>  	return 0;
>  }

[PATCH v2 2/2] hwmon: (dell-smm) Unify i8k_ioctl() and i8k_ioctl_unlocked()

[Armin Wolf]

The only purpose of i8k_ioctl() is to call i8k_ioctl_unlocked()
with i8k_mutex held. Judging from the hwmon code, this mutex
only needs to be held when setting the fan speed/mode, so
the operation of I8K_SET_FAN is guaranteed to be atomic.
Unify both functions and reduce the locking of i8k_mutex
to I8K_SET_FAN.

Tested on a Dell Inspiron 3505.

Signed-off-by: Armin Wolf <W_Armin@gmx.de>
---
 drivers/hwmon/dell-smm-hwmon.c | 28 +++++++++-------------------
 1 file changed, 9 insertions(+), 19 deletions(-)

diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
index 186d40938036..d8c6e75bb374 100644
--- a/drivers/hwmon/dell-smm-hwmon.c
+++ b/drivers/hwmon/dell-smm-hwmon.c
@@ -449,12 +449,12 @@ static int i8k_get_power_status(void)
  * Procfs interface
  */

-static int
-i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd, unsigned long arg)
+static long i8k_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)
 {
-	int val = 0;
-	int speed, err;
+	struct dell_smm_data *data = PDE_DATA(file_inode(fp));
 	int __user *argp = (int __user *)arg;
+	int speed, err;
+	int val = 0;

 	if (!argp)
 		return -EINVAL;
@@ -516,11 +516,13 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
 		if (copy_from_user(&speed, argp + 1, sizeof(int)))
 			return -EFAULT;

+		mutex_lock(&data->i8k_mutex);
 		err = i8k_set_fan(data, val, speed);
 		if (err < 0)
-			return err;
-
-		val = i8k_get_fan_status(data, val);
+			val = err;
+		else
+			val = i8k_get_fan_status(data, val);
+		mutex_unlock(&data->i8k_mutex);
 		break;

 	default:
@@ -536,18 +538,6 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
 	return 0;
 }

-static long i8k_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)
-{
-	struct dell_smm_data *data = PDE_DATA(file_inode(fp));
-	long ret;
-
-	mutex_lock(&data->i8k_mutex);
-	ret = i8k_ioctl_unlocked(fp, data, cmd, arg);
-	mutex_unlock(&data->i8k_mutex);
-
-	return ret;
-}
-
 /*
  * Print the information for /proc/i8k.
  */
--
2.30.2

Re: [PATCH v2 2/2] hwmon: (dell-smm) Unify i8k_ioctl() and i8k_ioctl_unlocked()

[Pali Rohár]

On Saturday 11 December 2021 16:54:22 Armin Wolf wrote:
> The only purpose of i8k_ioctl() is to call i8k_ioctl_unlocked()
> with i8k_mutex held. Judging from the hwmon code, this mutex
> only needs to be held when setting the fan speed/mode, so
> the operation of I8K_SET_FAN is guaranteed to be atomic.
> Unify both functions and reduce the locking of i8k_mutex
> to I8K_SET_FAN.
> 
> Tested on a Dell Inspiron 3505.
> 
> Signed-off-by: Armin Wolf <W_Armin@gmx.de>

Reviewed-by: Pali Rohár <pali@kernel.org>

> ---
>  drivers/hwmon/dell-smm-hwmon.c | 28 +++++++++-------------------
>  1 file changed, 9 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/hwmon/dell-smm-hwmon.c b/drivers/hwmon/dell-smm-hwmon.c
> index 186d40938036..d8c6e75bb374 100644
> --- a/drivers/hwmon/dell-smm-hwmon.c
> +++ b/drivers/hwmon/dell-smm-hwmon.c
> @@ -449,12 +449,12 @@ static int i8k_get_power_status(void)
>   * Procfs interface
>   */
> 
> -static int
> -i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd, unsigned long arg)
> +static long i8k_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)
>  {
> -	int val = 0;
> -	int speed, err;
> +	struct dell_smm_data *data = PDE_DATA(file_inode(fp));
>  	int __user *argp = (int __user *)arg;
> +	int speed, err;
> +	int val = 0;
> 
>  	if (!argp)
>  		return -EINVAL;
> @@ -516,11 +516,13 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
>  		if (copy_from_user(&speed, argp + 1, sizeof(int)))
>  			return -EFAULT;
> 
> +		mutex_lock(&data->i8k_mutex);
>  		err = i8k_set_fan(data, val, speed);
>  		if (err < 0)
> -			return err;
> -
> -		val = i8k_get_fan_status(data, val);
> +			val = err;
> +		else
> +			val = i8k_get_fan_status(data, val);
> +		mutex_unlock(&data->i8k_mutex);
>  		break;
> 
>  	default:
> @@ -536,18 +538,6 @@ i8k_ioctl_unlocked(struct file *fp, struct dell_smm_data *data, unsigned int cmd
>  	return 0;
>  }
> 
> -static long i8k_ioctl(struct file *fp, unsigned int cmd, unsigned long arg)
> -{
> -	struct dell_smm_data *data = PDE_DATA(file_inode(fp));
> -	long ret;
> -
> -	mutex_lock(&data->i8k_mutex);
> -	ret = i8k_ioctl_unlocked(fp, data, cmd, arg);
> -	mutex_unlock(&data->i8k_mutex);
> -
> -	return ret;
> -}
> -
>  /*
>   * Print the information for /proc/i8k.
>   */
> --
> 2.30.2
>