2019-05-30 06:48:27

by Krzysztof Adamski

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

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 <[email protected]>
---

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

2019-05-30 17:23:14

by Guenter Roeck

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

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 <[email protected]>
> ---
>
> 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
>

2019-05-31 10:14:08

by Krzysztof Adamski

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

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 <[email protected]>
>> ---
>>
>> 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

2019-06-03 13:14:03

by Alexander Sverdlin

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

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 <[email protected]>
> ---
>
> 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.

2019-06-03 16:21:02

by Guenter Roeck

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

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 <[email protected]>
> > ---
> >
> > 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