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

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Date:	Sun, 27 Oct 2013 14:24:07 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	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>
Subject: Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging request
 during shutdown

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.

Bjorn, don't you have a fix for this problem already done somewhere?

thanks,

greg k-h
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