Re: [BUG 3.12.rc4] Oops: unable to handle kernel paging requestduring shutdown

From: Veaceslav Falico
Date: Mon Oct 28 2013 - 13:33:35 EST

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@xxxxxxxxxxxxxxxxxxx> 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


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

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?

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