[PATCH] hwmon: pmbus: protect read-modify-write with lock

[PATCH] hwmon: pmbus: protect read-modify-write with lock

[Adamski, Krzysztof (Nokia - PL/Wroclaw)]

The operation done in the pmbus_update_fan() function is a
read-modify-write operation but it lacks any kind of lock protection
which may cause problems if run more than once simultaneously. This
patch uses an existing update_lock mutex to fix this problem.

Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
---

I'm resending this patch to proper recipients this time. Sorry if the
previous submission confused anybody.

 drivers/hwmon/pmbus/pmbus_core.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
index ef7ee90ee785..94adbede7912 100644
--- a/drivers/hwmon/pmbus/pmbus_core.c
+++ b/drivers/hwmon/pmbus/pmbus_core.c
@@ -268,6 +268,7 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
 	int rv;
 	u8 to;
 
+	mutex_lock(&data->update_lock);
 	from = pmbus_read_byte_data(client, page,
 				    pmbus_fan_config_registers[id]);
 	if (from < 0)
@@ -278,11 +279,15 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
 		rv = pmbus_write_byte_data(client, page,
 					   pmbus_fan_config_registers[id], to);
 		if (rv < 0)
-			return rv;
+			goto out;
 	}
 
-	return _pmbus_write_word_data(client, page,
-				      pmbus_fan_command_registers[id], command);
+	rv = _pmbus_write_word_data(client, page,
+				    pmbus_fan_command_registers[id], command);
+
+out:
+	mutex_lock(&data->update_lock);
+	return rv;
 }
 EXPORT_SYMBOL_GPL(pmbus_update_fan);
 
-- 
2.20.1

Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

[Guenter Roeck]

Hi,

On Thu, May 30, 2019 at 06:45:48AM +0000, Adamski, Krzysztof (Nokia - PL/Wroclaw) wrote:
> The operation done in the pmbus_update_fan() function is a
> read-modify-write operation but it lacks any kind of lock protection
> which may cause problems if run more than once simultaneously. This
> patch uses an existing update_lock mutex to fix this problem.
> 
> Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
> ---
> 
> I'm resending this patch to proper recipients this time. Sorry if the
> previous submission confused anybody.
> 
>  drivers/hwmon/pmbus/pmbus_core.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index ef7ee90ee785..94adbede7912 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -268,6 +268,7 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>  	int rv;
>  	u8 to;
>  
> +	mutex_lock(&data->update_lock);
>  	from = pmbus_read_byte_data(client, page,
>  				    pmbus_fan_config_registers[id]);
>  	if (from < 0)
> @@ -278,11 +279,15 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>  		rv = pmbus_write_byte_data(client, page,
>  					   pmbus_fan_config_registers[id], to);
>  		if (rv < 0)
> -			return rv;
> +			goto out;
>  	}
>  
> -	return _pmbus_write_word_data(client, page,
> -				      pmbus_fan_command_registers[id], command);
> +	rv = _pmbus_write_word_data(client, page,
> +				    pmbus_fan_command_registers[id], command);
> +
> +out:
> +	mutex_lock(&data->update_lock);

Should be mutex_unlock(), meaning you have not tested this ;-).

Either case, I think this is unnecessary. The function is (or should be)
always called with the lock already taken (ie with pmbus_set_sensor()
in the call path). If not, we would need a locked and an unlocked version
of this function to avoid lock recursion.

Thanks,
Guenter

> +	return rv;
>  }
>  EXPORT_SYMBOL_GPL(pmbus_update_fan);
>  
> -- 
> 2.20.1
> 

Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

[Adamski, Krzysztof (Nokia - PL/Wroclaw)]

On Thu, May 30, 2019 at 10:21:20AM -0700, Guenter Roeck wrote:
>Hi,
>
>On Thu, May 30, 2019 at 06:45:48AM +0000, Adamski, Krzysztof (Nokia - PL/Wroclaw) wrote:
>> The operation done in the pmbus_update_fan() function is a
>> read-modify-write operation but it lacks any kind of lock protection
>> which may cause problems if run more than once simultaneously. This
>> patch uses an existing update_lock mutex to fix this problem.
>>
>> Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
>> ---
>>
>> I'm resending this patch to proper recipients this time. Sorry if the
>> previous submission confused anybody.
>>
>>  drivers/hwmon/pmbus/pmbus_core.c | 11 ++++++++---
>>  1 file changed, 8 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
>> index ef7ee90ee785..94adbede7912 100644
>> --- a/drivers/hwmon/pmbus/pmbus_core.c
>> +++ b/drivers/hwmon/pmbus/pmbus_core.c
>> @@ -268,6 +268,7 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>>  	int rv;
>>  	u8 to;
>>
>> +	mutex_lock(&data->update_lock);
>>  	from = pmbus_read_byte_data(client, page,
>>  				    pmbus_fan_config_registers[id]);
>>  	if (from < 0)
>> @@ -278,11 +279,15 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>>  		rv = pmbus_write_byte_data(client, page,
>>  					   pmbus_fan_config_registers[id], to);
>>  		if (rv < 0)
>> -			return rv;
>> +			goto out;
>>  	}
>>
>> -	return _pmbus_write_word_data(client, page,
>> -				      pmbus_fan_command_registers[id], command);
>> +	rv = _pmbus_write_word_data(client, page,
>> +				    pmbus_fan_command_registers[id], command);
>> +
>> +out:
>> +	mutex_lock(&data->update_lock);
>
>Should be mutex_unlock(), meaning you have not tested this ;-).
>
>Either case, I think this is unnecessary. The function is (or should be)
>always called with the lock already taken (ie with pmbus_set_sensor()
>in the call path). If not, we would need a locked and an unlocked version
>of this function to avoid lock recursion.

You've got me :) I did not test that as I do not have a workflow using
this. I just stumbled opon this when looking at the code related to my
other patches. So it was more like a - "hey, shouldn't there be a lock
here?". But I was wrong, thanks.

Krzysztof

Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

[Sverdlin, Alexander (Nokia - DE/Ulm)]

Hi!

On 30/05/2019 08:45, Adamski, Krzysztof (Nokia - PL/Wroclaw) wrote:
> The operation done in the pmbus_update_fan() function is a
> read-modify-write operation but it lacks any kind of lock protection
> which may cause problems if run more than once simultaneously. This
> patch uses an existing update_lock mutex to fix this problem.
> 
> Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
> ---
> 
> I'm resending this patch to proper recipients this time. Sorry if the
> previous submission confused anybody.
> 
>  drivers/hwmon/pmbus/pmbus_core.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index ef7ee90ee785..94adbede7912 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -268,6 +268,7 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>  	int rv;
>  	u8 to;
>  
> +	mutex_lock(&data->update_lock);
>  	from = pmbus_read_byte_data(client, page,
>  				    pmbus_fan_config_registers[id]);
>  	if (from < 0)
> @@ -278,11 +279,15 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
>  		rv = pmbus_write_byte_data(client, page,
>  					   pmbus_fan_config_registers[id], to);
>  		if (rv < 0)
> -			return rv;
> +			goto out;
>  	}
>  
> -	return _pmbus_write_word_data(client, page,
> -				      pmbus_fan_command_registers[id], command);
> +	rv = _pmbus_write_word_data(client, page,
> +				    pmbus_fan_command_registers[id], command);
> +
> +out:
> +	mutex_lock(&data->update_lock);

This has to be mutex_unlock()...

> +	return rv;
>  }
>  EXPORT_SYMBOL_GPL(pmbus_update_fan);

-- 
Best regards,
Alexander Sverdlin.

Re: [PATCH] hwmon: pmbus: protect read-modify-write with lock

[Guenter Roeck]

On Mon, Jun 03, 2019 at 01:11:45PM +0000, Sverdlin, Alexander (Nokia - DE/Ulm) wrote:
> Hi!
> 
> On 30/05/2019 08:45, Adamski, Krzysztof (Nokia - PL/Wroclaw) wrote:
> > The operation done in the pmbus_update_fan() function is a
> > read-modify-write operation but it lacks any kind of lock protection
> > which may cause problems if run more than once simultaneously. This
> > patch uses an existing update_lock mutex to fix this problem.
> > 
> > Signed-off-by: Krzysztof Adamski <krzysztof.adamski@nokia.com>
> > ---
> > 
> > I'm resending this patch to proper recipients this time. Sorry if the
> > previous submission confused anybody.
> > 
> >  drivers/hwmon/pmbus/pmbus_core.c | 11 ++++++++---
> >  1 file changed, 8 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> > index ef7ee90ee785..94adbede7912 100644
> > --- a/drivers/hwmon/pmbus/pmbus_core.c
> > +++ b/drivers/hwmon/pmbus/pmbus_core.c
> > @@ -268,6 +268,7 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
> >  	int rv;
> >  	u8 to;
> >  
> > +	mutex_lock(&data->update_lock);
> >  	from = pmbus_read_byte_data(client, page,
> >  				    pmbus_fan_config_registers[id]);
> >  	if (from < 0)
> > @@ -278,11 +279,15 @@ int pmbus_update_fan(struct i2c_client *client, int page, int id,
> >  		rv = pmbus_write_byte_data(client, page,
> >  					   pmbus_fan_config_registers[id], to);
> >  		if (rv < 0)
> > -			return rv;
> > +			goto out;
> >  	}
> >  
> > -	return _pmbus_write_word_data(client, page,
> > -				      pmbus_fan_command_registers[id], command);
> > +	rv = _pmbus_write_word_data(client, page,
> > +				    pmbus_fan_command_registers[id], command);
> > +
> > +out:
> > +	mutex_lock(&data->update_lock);
> 
> This has to be mutex_unlock()...
> 

Not only that - it is also recursive.

Guenter