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

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Message-ID: <20131028173949.GG11209@redhat.com>
Date:	Mon, 28 Oct 2013 18:39:49 +0100
From:	Veaceslav Falico <vfalico@...hat.com>
To:	Bjorn Helgaas <bhelgaas@...gle.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 11:35:09AM -0600, Bjorn Helgaas wrote:
>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.

Will rebase and repost, sorry for all the noise about it :).

Thank you!

>
>Bjorn
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