[PATCH] i2c: do not use device name after device_unregister

[PATCH] i2c: do not use device name after device_unregister

[Thadeu Lima de Souza Cascardo]

dev_dbg outputs dev_name, which is released with device_unregister. This bug
resulted in output like this:

[ 7860.470713] i2c Xy2�0: adapter [SMBus I801 adapter at 1880] unregistered

The right output would be:
[   60.639233] i2c i2c-0: adapter [SMBus I801 adapter at 1880] unregistered

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
---
 drivers/i2c/i2c-core.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
index 0ac2f90..d5db0f4 100644
--- a/drivers/i2c/i2c-core.c
+++ b/drivers/i2c/i2c-core.c
@@ -843,6 +843,9 @@ int i2c_del_adapter(struct i2c_adapter *adap)
 				 adap->dev.parent);
 #endif
 
+	/* device name is gone after device_unregister */
+	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
+
 	/* clean up the sysfs representation */
 	init_completion(&adap->dev_released);
 	device_unregister(&adap->dev);
@@ -855,8 +858,6 @@ int i2c_del_adapter(struct i2c_adapter *adap)
 	idr_remove(&i2c_adapter_idr, adap->nr);
 	mutex_unlock(&core_lock);
 
-	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
-
 	/* Clear the device structure in case this adapter is ever going to be
 	   added again */
 	memset(&adap->dev, 0, sizeof(adap->dev));
-- 
1.6.5.7

Re: [PATCH] i2c: do not use device name after device_unregister

[Jean Delvare]

Hi Thadeu,

On Tue, 12 Jan 2010 19:36:43 -0200, Thadeu Lima de Souza Cascardo wrote:
> dev_dbg outputs dev_name, which is released with device_unregister. This bug
> resulted in output like this:
> 
> [ 7860.470713] i2c Xy2�0: adapter [SMBus I801 adapter at 1880] unregistered
> 
> The right output would be:
> [   60.639233] i2c i2c-0: adapter [SMBus I801 adapter at 1880] unregistered

I can't reproduce this bug. Do you have a specific memory poisoning
option enabled by any chance? And which kernel version are you running
exactly?

> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
> ---
>  drivers/i2c/i2c-core.c |    5 +++--
>  1 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 0ac2f90..d5db0f4 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -843,6 +843,9 @@ int i2c_del_adapter(struct i2c_adapter *adap)
>  				 adap->dev.parent);
>  #endif
>  
> +	/* device name is gone after device_unregister */
> +	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
> +
>  	/* clean up the sysfs representation */
>  	init_completion(&adap->dev_released);
>  	device_unregister(&adap->dev);
> @@ -855,8 +858,6 @@ int i2c_del_adapter(struct i2c_adapter *adap)
>  	idr_remove(&i2c_adapter_idr, adap->nr);
>  	mutex_unlock(&core_lock);
>  
> -	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
> -
>  	/* Clear the device structure in case this adapter is ever going to be
>  	   added again */
>  	memset(&adap->dev, 0, sizeof(adap->dev));

The device structure is embedded in struct i2c_adapter, so its memory
can't be reused before the i2c_adapter itself is freed, which can't
happen before the end of function i2c_del_adapter(). Until recently,
the device name was embedded in the device structure so the code above
was fine. But apparently this changed some 9 months ago...

-- 
Jean Delvare

Re: [PATCH] i2c: do not use device name after device_unregister

[Manu Abraham]

On Wed, Jan 13, 2010 at 2:25 PM, Jean Delvare <khali@linux-fr.org> wrote:
> Hi Thadeu,
>
> On Tue, 12 Jan 2010 19:36:43 -0200, Thadeu Lima de Souza Cascardo wrote:
>> dev_dbg outputs dev_name, which is released with device_unregister. This bug
>> resulted in output like this:
>>
>> [ 7860.470713] i2c Xy2�0: adapter [SMBus I801 adapter at 1880] unregistered
>>
>> The right output would be:
>> [   60.639233] i2c i2c-0: adapter [SMBus I801 adapter at 1880] unregistered
>
> I can't reproduce this bug. Do you have a specific memory poisoning
> option enabled by any chance? And which kernel version are you running
> exactly?


Same thing happens here with 2.6.30.5:

[11984.257365] i2c-adapter kkkkkkkkkkkkkkkkkkkkkkkkkkkkkkk�[�t��
 : adapter [SAA716x I2C Core 0] unregistered

Regards,
Manu

Re: [PATCH] i2c: do not use device name after device_unregister

[Thadeu Lima de Souza Cascardo]

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On Wed, Jan 13, 2010 at 11:25:15AM +0100, Jean Delvare wrote:
> Hi Thadeu,
> 
> On Tue, 12 Jan 2010 19:36:43 -0200, Thadeu Lima de Souza Cascardo wrote:
> > dev_dbg outputs dev_name, which is released with device_unregister. This bug
> > resulted in output like this:
> > 
> > [ 7860.470713] i2c Xy2�0: adapter [SMBus I801 adapter at 1880] unregistered
> > 
> > The right output would be:
> > [   60.639233] i2c i2c-0: adapter [SMBus I801 adapter at 1880] unregistered
> 
> I can't reproduce this bug. Do you have a specific memory poisoning
> option enabled by any chance? And which kernel version are you running
> exactly?
> 

I'm not using any memory poisoning option that I'm aware of. However, I've been
using SLOB as an allocator, which may make a pretty difference, I guess.

I was running some of Linus' latest published git versions, something on top of
v2.6.33-rc3, commit 2c1f1895ef2aa8f0e5497893eff71304aef332e1.

> > 
> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
> > ---
> >  drivers/i2c/i2c-core.c |    5 +++--
> >  1 files changed, 3 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> > index 0ac2f90..d5db0f4 100644
> > --- a/drivers/i2c/i2c-core.c
> > +++ b/drivers/i2c/i2c-core.c
> > @@ -843,6 +843,9 @@ int i2c_del_adapter(struct i2c_adapter *adap)
> >  				 adap->dev.parent);
> >  #endif
> >  
> > +	/* device name is gone after device_unregister */
> > +	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
> > +
> >  	/* clean up the sysfs representation */
> >  	init_completion(&adap->dev_released);
> >  	device_unregister(&adap->dev);
> > @@ -855,8 +858,6 @@ int i2c_del_adapter(struct i2c_adapter *adap)
> >  	idr_remove(&i2c_adapter_idr, adap->nr);
> >  	mutex_unlock(&core_lock);
> >  
> > -	dev_dbg(&adap->dev, "adapter [%s] unregistered\n", adap->name);
> > -
> >  	/* Clear the device structure in case this adapter is ever going to be
> >  	   added again */
> >  	memset(&adap->dev, 0, sizeof(adap->dev));
> 
> The device structure is embedded in struct i2c_adapter, so its memory
> can't be reused before the i2c_adapter itself is freed, which can't
> happen before the end of function i2c_del_adapter(). Until recently,
> the device name was embedded in the device structure so the code above
> was fine. But apparently this changed some 9 months ago...
> 

The device may not be reused, but it's name is in its kobject, which allocates
memory using kvasprintf, and releases it when device_del ends up calling
kobject_put. So, anyway, we should not access memory that has been released. I
guess trying some poisoning option or changing to SLOB may help you hit the
bug.

> -- 
> Jean Delvare

Best Regards,
Cascardo.

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