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SubjectRe: [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@linuxfoundation.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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