linux-kernel - Re: [RFC PATCH v8 0/5] IPC: checkpoint/restore in userspace enhancements

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Date:	Mon, 14 Jan 2013 01:31:04 -0500
From:	Sasha Levin <levinsasha928@...il.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	serge.hallyn@...onical.com, ebiederm@...ssion.com,
	linux-kernel@...r.kernel.org, xemul@...allels.com,
	catalin.marinas@....com, will.deacon@....com, jmorris@...ei.org,
	cmetcalf@...era.com, joe.korty@...r.com, dhowells@...hat.com,
	dledford@...hat.com, viro@...iv.linux.org.uk,
	kosaki.motohiro@...fujitsu.com, linux-api@...r.kernel.org,
	serue@...ibm.com, tglx@...utronix.de, paulmck@...ux.vnet.ibm.com,
	devel@...nvz.org, mtk.manpages@...il.com,
	Wu Fengguang <fengguang.wu@...el.com>
Subject: Re: [RFC PATCH v8 0/5] IPC: checkpoint/restore in userspace enhancements

On Wed, Jan 9, 2013 at 3:24 AM, Stanislav Kinsbursky
<skinsbursky@...allels.com> wrote:
> 22.12.2012 19:43, Sasha Levin пишет:
>
>> On 12/21/2012 04:57 PM, Sasha Levin wrote:
>>>
>>> On 12/21/2012 03:46 PM, Stanislav Kinsbursky wrote:
>>>>
>>>> 21.12.2012 00:47, Andrew Morton пишет:
>>>>>
>>>>> On Thu, 20 Dec 2012 08:06:32 +0400
>>>>> Stanislav Kinsbursky<skinsbursky@...allels.com>  wrote:
>>>>>
>>>>>> 19.12.2012 00:36, Andrew Morton __________:
>>>>>>>
>>>>>>> On Wed, 24 Oct 2012 19:34:51 +0400
>>>>>>> Stanislav Kinsbursky<skinsbursky@...allels.com>  wrote:
>>>>>>>
>>>>>>>> This respin of the patch set was significantly reworked. Most part
>>>>>>>> of new API
>>>>>>>> was replaced by sysctls (by one per messages, semaphores and shared
>>>>>>>> memory),
>>>>>>>> allowing to preset desired id for next new IPC object.
>>>>>>>>
>>>>>>>> This patch set is aimed to provide additional functionality for all
>>>>>>>> IPC
>>>>>>>> objects, which is required for migration of these objects by
>>>>>>>> user-space
>>>>>>>> checkpoint/restore utils (CRIU).
>>>>>>>>
>>>>>>>> The main problem here was impossibility to set up object id. This
>>>>>>>> patch set
>>>>>>>> solves the problem by adding new sysctls for preset of desired id
>>>>>>>> for new IPC
>>>>>>>> object.
>>>>>>>>
>>>>>>>> Another problem was to peek messages from queues without deleting
>>>>>>>> them.
>>>>>>>> This was achived by introducing of new MSG_COPY flag for
>>>>>>>> sys_msgrcv(). If
>>>>>>>> MSG_COPY flag is set, then msgtyp is interpreted as message number.
>>>>>>>
>>>>>>> According to my extensive records, Sasha hit a bug in
>>>>>>> ipc-message-queue-copy-feature-introduced.patch and Fengguang found a
>>>>>>> bug in
>>>>>>>
>>>>>>> ipc-message-queue-copy-feature-introduced-cleanup-do_msgrcv-aroung-msg_copy-feature.patch
>>>>>>>
>>>>>>> It's not obvious (to me) that these things have been identified and
>>>>>>> fixed.  What's the status, please?
>>>>>>
>>>>>> Hello, Andrew.
>>>>>> Fengguang's issue was solved by "ipc: simplify message copying" I sent
>>>>>> you.
>>>>>> But I can't find Sasha's issue. As I remember, there was some problem
>>>>>> in
>>>>>> early
>>>>>> version of the patch set. But I believe its fixed now.
>>>>>
>>>>> http://lkml.indiana.edu/hypermail/linux/kernel/1210.3/01710.html
>>>>>
>>>>> Subject: "ipc, msgqueue: NULL ptr deref in msgrcv"
>>>>
>>>>
>>>> Ah, yes. Thanks.
>>>> Hi found it in initial version of code, which was significantly changed
>>>> (or cleaned and simplified) by further patch series.
>>>> And I cant find out, how this can happen, because this patch he bisect
>>>> to do not modify the queue itself, while he found the
>>>> problem in testmsg.
>>>
>>>
>>> I actually can't reproduce it on the latest -next.
>>>
>>> I was reverting the IPC changes in the past couple of weeks so that I
>>> could test the
>>> rest of the IPC code with the fuzzer, and when I added them back in again
>>> I can't
>>> reproduce the issue I've reported earlier.
>>>
>>> We can probably figure out where it got fixed by bisecting between -next
>>> trees if anyone
>>> is interested in that.
>>
>>
>> Ignore that. It just took more fuzzing to stumble on it again:
>>
>
> Hello, Sasha!
> Thanks!
> But I still can't understand, how this can happen... And I can't reproduce.
> Could you specify your load? I.e. how do you stumble on this panic?
> Looks like you don't use new "copy" feature.

I just fuzz with trinity
(http://git.codemonkey.org.uk/?p=trinity.git;a=tree) inside a pretty
basic KVM guest.


Thanks,
Sasha
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