[PATCH] hwmon: (ads7871) Fix ads7871_probe error path

[PATCH] hwmon: (ads7871) Fix ads7871_probe error path

[Axel Lin]

We need to call hwmon_device_unregister() if an error is detected after
sucessfully register hwmon device.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
---
 drivers/hwmon/ads7871.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c
index b300a20..303db92 100644
--- a/drivers/hwmon/ads7871.c
+++ b/drivers/hwmon/ads7871.c
@@ -201,11 +201,13 @@ static int __devinit ads7871_probe(struct spi_device *spi)
 	we need to make sure we really have a chip*/
 	if (val != ret) {
 		err = -ENODEV;
-		goto error_remove;
+		goto error_unregister;
 	}
 
 	return 0;
 
+error_unregister:
+	hwmon_device_unregister(pdata->hwmon_dev);
 error_remove:
 	sysfs_remove_group(&spi->dev.kobj, &ads7871_group);
 error_free:
-- 
1.7.2

Re: [PATCH] hwmon: (ads7871) Fix ads7871_probe error path

[Jean Delvare]

Hi Alex,

On Mon, 16 Aug 2010 09:31:17 +0800, Axel Lin wrote:
> We need to call hwmon_device_unregister() if an error is detected after
> sucessfully register hwmon device.
> 
> Signed-off-by: Axel Lin <axel.lin@gmail.com>
> ---
>  drivers/hwmon/ads7871.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c
> index b300a20..303db92 100644
> --- a/drivers/hwmon/ads7871.c
> +++ b/drivers/hwmon/ads7871.c
> @@ -201,11 +201,13 @@ static int __devinit ads7871_probe(struct spi_device *spi)
>  	we need to make sure we really have a chip*/
>  	if (val != ret) {
>  		err = -ENODEV;
> -		goto error_remove;
> +		goto error_unregister;
>  	}
>  
>  	return 0;
>  
> +error_unregister:
> +	hwmon_device_unregister(pdata->hwmon_dev);
>  error_remove:
>  	sysfs_remove_group(&spi->dev.kobj, &ads7871_group);
>  error_free:

The bug is real, but I don't think the fix is correct. You should never
have to unregister the hwmon device in the error path, because you
should ensure the hardware is there and working _before_ you register
the hwmon device.

User-space could watch for hwmon devices being added or removed, and
you don't want to trigger such events for a device which isn't going to
work.

So I would suggest reworking the order in which things are done,
leaving hwmon_device_register() at the end of the function. This won't
only fix the error path, this will also close a race window, as for the
moment, the device is exposed to user-space _before_ it it properly
initialized, which is wrong.

Please send an updated patch and I'll be happy to apply it.

-- 
Jean Delvare

Re: [PATCH] hwmon: (ads7871) Fix ads7871_probe error path

[Paul Thomas]

On Tue, Aug 17, 2010 at 4:07 AM, Jean Delvare <khali@linux-fr.org> wrote:
> Hi Alex,
>
> On Mon, 16 Aug 2010 09:31:17 +0800, Axel Lin wrote:
>> We need to call hwmon_device_unregister() if an error is detected after
>> sucessfully register hwmon device.
>>
>> Signed-off-by: Axel Lin <axel.lin@gmail.com>
>> ---
>>  drivers/hwmon/ads7871.c |    4 +++-
>>  1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c
>> index b300a20..303db92 100644
>> --- a/drivers/hwmon/ads7871.c
>> +++ b/drivers/hwmon/ads7871.c
>> @@ -201,11 +201,13 @@ static int __devinit ads7871_probe(struct spi_device *spi)
>>       we need to make sure we really have a chip*/
>>       if (val != ret) {
>>               err = -ENODEV;
>> -             goto error_remove;
>> +             goto error_unregister;
>>       }
>>
>>       return 0;
>>
>> +error_unregister:
>> +     hwmon_device_unregister(pdata->hwmon_dev);
>>  error_remove:
>>       sysfs_remove_group(&spi->dev.kobj, &ads7871_group);
>>  error_free:
>
> The bug is real, but I don't think the fix is correct. You should never
> have to unregister the hwmon device in the error path, because you
> should ensure the hardware is there and working _before_ you register
> the hwmon device.
>
> User-space could watch for hwmon devices being added or removed, and
> you don't want to trigger such events for a device which isn't going to
> work.
>
> So I would suggest reworking the order in which things are done,
> leaving hwmon_device_register() at the end of the function. This won't
> only fix the error path, this will also close a race window, as for the
> moment, the device is exposed to user-space _before_ it it properly
> initialized, which is wrong.
>
> Please send an updated patch and I'll be happy to apply it.
>
> --
> Jean Delvare
>

Should the kzalloc,  sysfs_create_group and hwmon_device_register all
stay in the same order just following the register check? I can send a
patch for that.

thanks,
Paul

Re: [PATCH] hwmon: (ads7871) Fix ads7871_probe error path

[Jean Delvare]

On Tue, 17 Aug 2010 08:15:59 -0700, Paul Thomas wrote:
> On Tue, Aug 17, 2010 at 4:07 AM, Jean Delvare <khali@linux-fr.org> wrote:
> > Hi Alex,
> >
> > On Mon, 16 Aug 2010 09:31:17 +0800, Axel Lin wrote:
> >> We need to call hwmon_device_unregister() if an error is detected after
> >> sucessfully register hwmon device.
> >>
> >> Signed-off-by: Axel Lin <axel.lin@gmail.com>
> >> ---
> >>  drivers/hwmon/ads7871.c |    4 +++-
> >>  1 files changed, 3 insertions(+), 1 deletions(-)
> >>
> >> diff --git a/drivers/hwmon/ads7871.c b/drivers/hwmon/ads7871.c
> >> index b300a20..303db92 100644
> >> --- a/drivers/hwmon/ads7871.c
> >> +++ b/drivers/hwmon/ads7871.c
> >> @@ -201,11 +201,13 @@ static int __devinit ads7871_probe(struct spi_device *spi)
> >>       we need to make sure we really have a chip*/
> >>       if (val != ret) {
> >>               err = -ENODEV;
> >> -             goto error_remove;
> >> +             goto error_unregister;
> >>       }
> >>
> >>       return 0;
> >>
> >> +error_unregister:
> >> +     hwmon_device_unregister(pdata->hwmon_dev);
> >>  error_remove:
> >>       sysfs_remove_group(&spi->dev.kobj, &ads7871_group);
> >>  error_free:
> >
> > The bug is real, but I don't think the fix is correct. You should never
> > have to unregister the hwmon device in the error path, because you
> > should ensure the hardware is there and working _before_ you register
> > the hwmon device.
> >
> > User-space could watch for hwmon devices being added or removed, and
> > you don't want to trigger such events for a device which isn't going to
> > work.
> >
> > So I would suggest reworking the order in which things are done,
> > leaving hwmon_device_register() at the end of the function. This won't
> > only fix the error path, this will also close a race window, as for the
> > moment, the device is exposed to user-space _before_ it it properly
> > initialized, which is wrong.
> >
> > Please send an updated patch and I'll be happy to apply it.
> >
> > --
> > Jean Delvare
> >
> 
> Should the kzalloc,  sysfs_create_group and hwmon_device_register all
> stay in the same order just following the register check? I can send a
> patch for that.

Axel already sent an updated patch, so it's all OK.

-- 
Jean Delvare