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Date: Wed, 30 May 2007 11:58:22 +0200
From: Christoph Hellwig <hch@lst.de>
To: Arnd Bergmann <arnd@arndb.de>
Cc: cbe-oss-dev@ozlabs.org, gregkh@suse.de, linux-kernel@vger.kernel.org
Subject: Re: [Cbe-oss-dev] [RFC] Cell: shutdown method for spu_sysdev_class
Message-ID: <20070530095821.GA24373@lst.de>
References: <463D1A2F.10708@am.sony.com> <200705292023.49968.arnd@arndb.de>
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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.