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

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Message-ID: <CAErSpo5NmBDqRA3URAQPmw4iC3xvpDdd9JFROuftLJE1YsbPhA@mail.gmail.com>
Date:	Mon, 28 Oct 2013 11:23:41 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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

[+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*.

Bjorn
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