linux-kernel - Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging request during shutdown

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Date:	Mon, 28 Oct 2013 11:52:25 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <yinghai@...nel.org>,
	Knut Petersen <Knut_Petersen@...nline.de>,
	Ingo Molnar <mingo@...nel.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Veaceslav Falico <vfalico@...hat.com>
Subject: Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging request
 during shutdown

On Mon, Oct 28, 2013 at 11:23:41AM -0600, Bjorn Helgaas wrote:
> [+cc Veaceslav]
> 
> On Sun, Oct 27, 2013 at 3:24 PM, Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> > On Sun, Oct 27, 2013 at 09:13:29PM +0000, Linus Torvalds wrote:
> >> .. and one more case of freeing a delayed work object (likely a kobject again):
> >>
> >> This time it looks like it's in the PCI layer, freeing the msi irq information.
> >>
> >> It looks like that code simply does
> >>
> >>     kobject_del(&entry->kobj);
> >>     kobject_put(&entry->kobj);
> >>     list_del(&entry->list);
> >>     kfree(entry);
> >>
> >> and the problem is that the "entry->kobj" may have *other* references
> >> to it, thanks to people accessing it through /sys, so despite doing a
> >> kojbect_del/kobject_put(), it's not at all ok to then do a "kfree()"
> >> on it. The embedded kobj might still be in use.
> >>
> >> Afaik, that code should do the kfree() on the kobject in the _release_
> >> method, not synchronously like that.
> >>
> >> We already have a msi_kobj_release(), I'm wondering why that doesn't
> >> do the kfree().
> >>
> >> Bjorn? Yinghai? Greg, comments about that msi kobj usage?
> >
> > Ick, it really should be doing a kfree() in the release only.  Bjorn has
> > had a bunch of changes in this area recently, perhaps they are in
> > linux-next waiting for 3.13, and I've talked to him about getting rid of
> > all of the kobjects for msi files, as I don't think it's needed at all.
> 
> IIRC, you said you might take a look at converting this to attributes
> on the train back home, so I haven't looked into it myself :)

Yes, I was supposed to, but James and I ended up splitting a bottle of
wine on the train, and it's not a good idea to do driver model work with
wine.  Hard liquor is usually needed :)

It's on my todo list...

thanks,

greg k-h
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