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 11:35:09 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Veaceslav Falico <vfalico@...hat.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	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>
Subject: Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging request
 during shutdown

On Mon, Oct 28, 2013 at 11:30 AM, Veaceslav Falico <vfalico@...hat.com> wrote:
> 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 :)
>>
>>> Bjorn, don't you have a fix for this problem already done somewhere?
>>
>>
>> Yep, this is clearly wrong, and Veaceslav has a patch that moves the
>> kfree() to the release function.  I've been waiting for a consolidated
>> repost of all his MSI-related fixes, but maybe he's been waiting for
>> *me*.
>
>
> https://lkml.org/lkml/2013/10/9/170
>
> My patchset is ready to be applied, in its v2 state.
>
> Except that the bits with kobject_del() (theoretical race) - which are done
> in your patch "kobject: remove kset from sysfs immediately in
> kset_unregister()", though I didn't see it accepted.
>
> Should I re-send the patchset?

Can you please repost it?  That will be easier for me than digging
individual messages out of the archives.  Thanks, and sorry for my
confusion.

Bjorn
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