linux-kernel - Re: [RFC PATCH v2 next]module: Fix mod->mkobj.kobj potentially freed too early

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Date:	Mon, 26 Aug 2013 23:21:35 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Li Zhong <zhong@...ux.vnet.ibm.com>,
	linux-next list <linux-next@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>, rmk+kernel@....linux.org.uk
Subject: Re: [RFC PATCH v2 next]module: Fix mod->mkobj.kobj potentially freed
 too early

On Tue, Aug 27, 2013 at 02:08:27PM +0930, Rusty Russell wrote:
> Greg KH <gregkh@...uxfoundation.org> writes:
> > On Thu, Aug 22, 2013 at 03:37:55PM +0800, Li Zhong wrote:
> >> DEBUG_KOBJECT_RELEASE helps to find the issue attached below.
> > People are starting to hit these types of issues, and I'd like to take
> > this one out of the picture.
> >
> > Rusty, any objection to me taking this through my driver-core tree,
> > where this new config option shows up?
> 
> The original fix was better.
> 
> Moving the module_kobject out and giving it its own lifetime solves this
> immediate issue, but it still means there's an accessible module_kobject
> around referring to a module which doesn't exist any more.

That's ok, it could happen before as well.  What's wrong with that?

> Original copied below, feel free to take it.

You are just sitting and sleeping until someone drops the last reference
to the module.  What if userspace grabs a reference from sysfs?  That
could never return, I don't think you want to stall that out.

I'd prefer not having 2 things determining the lifecycle of a single
object, that's messy, and not needed at all.

thanks,

greg k-h
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