Re: [Cbe-oss-dev] [RFC] Cell: shutdown method for spu_sysdev_class

Re: [Cbe-oss-dev] [RFC] Cell: shutdown method for spu_sysdev_class

[Arnd Bergmann]

On Sunday 06 May 2007, Geoff Levand wrote:
> --- ps3-linux-dev.orig/arch/powerpc/platforms/cell/spu_base.c
> +++ ps3-linux-dev/arch/powerpc/platforms/cell/spu_base.c
> @@ -463,8 +463,21 @@ void spu_free(struct spu *spu)
>  }
>  EXPORT_SYMBOL_GPL(spu_free);
>
> +static int spu_shutdown(struct sys_device *sysdev)
> +{
> +       struct spu *spu = container_of(sysdev, struct spu, sysdev);
> +
> +       // what else here???
> +
> +       spu_free_irqs(spu);
> +       spu_destroy_spu(spu);
> +       kfree(spu);
> +       return 0;
> +}
> +
>  struct sysdev_class spu_sysdev_class = {
> -       set_kset_name("spu")
> +       set_kset_name("spu"),
> +       .shutdown = spu_shutdown,
>  };
>
>  int spu_add_sysdev_attr(struct sysdev_attribute *attr)

After some debugging, I found that this patch creates an oops when slab
debugging is enabled, the reason for that being that sysdev_shutdown()
iterates over all system devices using list_for_each_entry(), not
list_for_each_entry_safe().

There are two ways of fixing this:

- use list_for_each_entry_safe() to go over all devices so they
  can be freed in their ->shutdown method.
- not free the device, because we know the system is going down
  anyway.

Is it documented or implied somewhere that ->shutdown must not free
the device? If not, the first option is probably the safer choice.

	Arnd <><

Re: [Cbe-oss-dev] [RFC] Cell: shutdown method for spu_sysdev_class

[Christoph Hellwig]

On Tue, May 29, 2007 at 08:23:49PM +0200, Arnd Bergmann wrote:
> On Sunday 06 May 2007, Geoff Levand wrote:
> > --- ps3-linux-dev.orig/arch/powerpc/platforms/cell/spu_base.c
> > +++ ps3-linux-dev/arch/powerpc/platforms/cell/spu_base.c
> > @@ -463,8 +463,21 @@ void spu_free(struct spu *spu)
> >  }
> >  EXPORT_SYMBOL_GPL(spu_free);
> >
> > +static int spu_shutdown(struct sys_device *sysdev)
> > +{
> > +       struct spu *spu = container_of(sysdev, struct spu, sysdev);
> > +
> > +       // what else here???
> > +
> > +       spu_free_irqs(spu);
> > +       spu_destroy_spu(spu);
> > +       kfree(spu);
> > +       return 0;
> > +}
> > +
> >  struct sysdev_class spu_sysdev_class = {
> > -       set_kset_name("spu")
> > +       set_kset_name("spu"),
> > +       .shutdown = spu_shutdown,
> >  };
> >
> >  int spu_add_sysdev_attr(struct sysdev_attribute *attr)
> 
> After some debugging, I found that this patch creates an oops when slab
> debugging is enabled, the reason for that being that sysdev_shutdown()
> iterates over all system devices using list_for_each_entry(), not
> list_for_each_entry_safe().
> 
> There are two ways of fixing this:
> 
> - use list_for_each_entry_safe() to go over all devices so they
>   can be freed in their ->shutdown method.
> - not free the device, because we know the system is going down
>   anyway.
> 
> Is it documented or implied somewhere that ->shutdown must not free
> the device? If not, the first option is probably the safer choice.

It's not documented anywhere, but implicitly assumed.  I don't know
of any shutdown implementation that frees the device.

Re: [Cbe-oss-dev] [RFC] Cell: shutdown method for spu_sysdev_class

[Arnd Bergmann]

On Wednesday 30 May 2007, Christoph Hellwig wrote:
> 
> > Is it documented or implied somewhere that ->shutdown must not free
> > the device? If not, the first option is probably the safer choice.
> 
> It's not documented anywhere, but implicitly assumed.  I don't know
> of any shutdown implementation that frees the device.

Right, I found the explanation now myself:

The ->shutdown method is called for system devices that are still
part of a linked linked list. Freeing the object would destroy that
list.

Geoff, please merge the patch below in your tree.

	Arnd <><
---

Subject: cell: don't free spu objects in sysdev shutdown

From: Arnd Bergmann <arnd.bergmann@de.ibm.com>
System devices are accessed after they are shut down, so
we must not free the data structures.

Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Index: linux-2.6/arch/powerpc/platforms/cell/spu_base.c
===================================================================
--- linux-2.6.orig/arch/powerpc/platforms/cell/spu_base.c
+++ linux-2.6/arch/powerpc/platforms/cell/spu_base.c
@@ -517,7 +517,6 @@ static int spu_shutdown(struct sys_devic
 
 	spu_free_irqs(spu);
 	spu_destroy_spu(spu);
-	kfree(spu);
 	return 0;
 }