On Wed, 2013-08-21 at 21:03 -0700, Greg KH wrote:
> On Thu, Aug 22, 2013 at 10:34:06AM +0800, Li Zhong wrote:
> > On Wed, 2013-08-21 at 09:18 -0700, Greg KH wrote:
> > > On Wed, Aug 21, 2013 at 05:49:58PM +0800, Li Zhong wrote:
> > > > DEBUG_KOBJECT_RELEASE helps to find the issue attached below.
> > > >
> > > > After some investigation, it seems the reason is:
> > > > The mod->mkobj.kobj(ffffffffa01600d0 below) is freed together with mod
> > > > itself in free_module(). However, its children still hold references to
> > > > it, as the delay caused by DEBUG_KOBJECT_RELEASE. So when the
> > > > child(holders below) tries to decrease the reference count to its parent
> > > > in kobject_del(), BUG happens as it tries to access already freed memory.
> > >
> > > Ah, thanks for tracking this down. I had seen this in my local testing,
> > > but wasn't able to figure out the offending code.
> > >
> > > > This patch tries to fix it by waiting for the mod->mkobj.kobj to be
> > > > really released in the module removing process (and some error code
> > > > paths).
> > >
> > > Nasty, we should just be freeing the structure in the release function,
> > > why doesn't that work?
> >
> > Hi Greg,
> >
> > It seems I didn't describe it clearly in the previous mail. I'm trying
> > to do it better below:
> >
> > mod->mkobj.kobj is embedded in module_kobject(not a pointer):
> > struct module_kobject {
> > struct kobject kobj;
> > ...
> >
> > and allocated with the module memory. So we could see the parent below
> > ffffffffa01600d0 is between MODULES_VADDR (ffffffffa0000000) and
> > MODULES_END(ffffffffff000000).
> >
> > It seem to me that the mkobj.kobj is freed by module_free(mod,
> > mod->module_core).
>
> Ick, you are right. If a kobject is being embedded in an object, it
> should control the lifespan of the object, not somewhere else like is
> happening here.
>
> The best solution for this is to make the kobject a pointer, not
> embedded in the structure, that will fix this issue, right?
Yes, I think so. I'll try to write a fix using this way, thanks for your
suggestion.
Thanks, Zhong
>
> thanks,
>
> greg k-h
>
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