[CRIU] Fix cpuset restore-in-root bug

[Pavel Emelyanov]

On 10/08/2014 06:25 PM, Pavel Emelyanov wrote:
> On 10/08/2014 06:16 PM, Tycho Andersen wrote:
>> On Wed, Oct 08, 2014 at 06:02:04PM +0400, Pavel Emelyanov wrote:
>>> On 10/08/2014 05:57 PM, Pavel Emelyanov wrote:
>>>> On 10/08/2014 02:43 AM, Tycho Andersen wrote:
>>>>> Hi Pavel,
>>>>>
>>>>> On Tue, Oct 07, 2014 at 03:58:39PM -0500, Tycho Andersen wrote:
>>>>>> On Tue, Oct 07, 2014 at 11:15:34PM +0400, Pavel Emelyanov wrote:
>>>>>>> On 10/07/2014 06:16 PM, Tycho Andersen wrote:
>>>>>>>> Hi Pavel,
>>>>>>>>
>>>>>>>> On Tue, Oct 07, 2014 at 12:58:34PM +0400, Pavel Emelyanov wrote:
>>>>>>>>> On 10/06/2014 06:03 PM, Tycho Andersen wrote:
>>>>>>>>>> Hi all,
>>>>>>>>>>
>>>>>>>>>> Based on some discussion, we shouldn't try to do any intelligent copying of any
>>>>>>>>>> properties anywhere else in the tree. These cpuset properties are special only
>>>>>>>>>> in the sense that they need to be restored before the move_in_cgroup call, and
>>>>>>>>>> if the parent cgroups have conflicting options (or empty options), it is best
>>>>>>>>>> to just let the restore fail.
>>>>>>>>>
>>>>>>>>> Patches applied, thanks!
>>>>>>>>>
>>>>>>>>>> Also, I noticed when making this patch that I am getting a lot of:
>>>>>>>>>>
>>>>>>>>>> (00.092575)    290: Error (util.c:101): Unable to close fd 1016: Bad file descriptor
>>>>>>>>>
>>>>>>>>> Ouch. Can you show the full log please?
>>>>>>>>
>>>>>>>> Yes, these are with the current master:
>>>>>>>>
>>>>>>>> http://paste.ubuntu.com/8514798/
>>>>>>>
>>>>>>> Hm... I've run cgroup* tests on recent HEAD and no errors in logs.
>>>>>>>
>>>>>>>> also, 1016 is the cg service fd, so it seems like maybe a recent
>>>>>>>> reordering broke something? I can do a bisect if you take a look at
>>>>>>>> the log and nothing obvious pops out.
>>>>>>>
>>>>>>> Yes, please. If you would be able to shed more light on this, that
>>>>>>> would be awesome.
>>>>>>
>>>>>> Hmm. I tried to bisect with a patch that I know I wasn't seeing this
>>>>>> problem with, but even that one has this issue now. Something about my
>>>>>> environment must have changed, I guess? I will investigate more and
>>>>>> keep you posted.
>>>>>
>>>>> The patch below fixes the issue for me. Does it make sense? I have no
>>>>> idea why we/I didn't see this earlier.
>>>>>
>>>>> Tycho
>>>>>
>>>>>
>>>>>
>>>>> >From 0f3aad8a78aee56ff7794db33cf76c5d5aae5039 Mon Sep 17 00:00:00 2001
>>>>> From: Tycho Andersen <tycho.andersen at canonical.com>
>>>>> Date: Tue, 7 Oct 2014 17:25:26 -0500
>>>>> Subject: [PATCH] restore: don't race when closing cg yard
>>>>>
>>>>> If CLONE_FILES is set, we only have one copy of the cg yard fd, so we shouldn't
>>>>> all close it. Further, we should wait to close it until after the FORKING stage
>>>>> is done, since it is needed during that stage.
>>>>>
>>>>> If CLONE_FILES is not set, each process can safely close their copy of the fd.
>>>>>
>>>>> Signed-off-by: Tycho Andersen <tycho.andersen at canonical.com>
>>>>> ---
>>>>>  cr-restore.c | 17 +++++++++--------
>>>>>  1 file changed, 9 insertions(+), 8 deletions(-)
>>>>>
>>>>> diff --git a/cr-restore.c b/cr-restore.c
>>>>> index fd35bef..c12d28e 100644
>>>>> --- a/cr-restore.c
>>>>> +++ b/cr-restore.c
>>>>> @@ -1461,14 +1461,6 @@ static int restore_task_with_children(void *_arg)
>>>>>  	if (create_children_and_session())
>>>>>  		goto err_fini_mnt;
>>>>>  
>>>>> -	/*
>>>>> -	 * This must be done after forking to allow child
>>>>> -	 * to get the cgroup fd so it can move into the
>>>>> -	 * correct /tasks file if it is in a different cgroup
>>>>> -	 * set than its parent
>>>>> -	 */
>>>>> -	close_service_fd(CGROUP_YARD);
>>>>> -
>>>>>  	if (restore_task_mnt_ns(current))
>>>>>  		goto err_fini_mnt;
>>>>>  
>>>>> @@ -1480,6 +1472,15 @@ static int restore_task_with_children(void *_arg)
>>>>>  	if (restore_finish_stage(CR_STATE_FORKING) < 0)
>>>>>  		goto err_fini_mnt;
>>>>>  
>>>>> +	/*
>>>>> +	 * This must be done after forking to allow child
>>>>> +	 * to get the cgroup fd so it can move into the
>>>>> +	 * correct /tasks file if it is in a different cgroup
>>>>> +	 * set than its parent
>>>>> +	 */
>>>>> +	if (!(ca->clone_flags & CLONE_FILES) || current->parent == NULL)
>>>>> +		close_service_fd(CGROUP_YARD);
>>>>
>>>> I think what really makes sense here is the CLONE_FILES check, because
>>>> all children forking happens in create_children_and_session().
>>>>
>>>> And it looks like I know why this appeared only recently -- the helper
>>>> tasks are now created with CLONE_FILES, so we may have a lot of helpers.
>>>
>>> After a bit more thinking and reading the code. The place where this close
>>> is called also matters -- if we close CGYARD before other tasks forked, the
>>> latter ones may fail to obtain this service fd.
>>
>> Yeah, it isn't necessarily clear from the diff, but I moved it after
>> the FORKING stage to avoid this problem.
> 
> Yes, and this is also correct. I'm still thinking about the CLONE_FILES check.
> 
>>> And one more notice -- it looks like we have generic service descriptors 
>>> closing problem. Helpers inherit files table from parent but close the
>>> descriptors.
>>
>> By this you mean that there are some other bugs like this as well?
> 
> Should be -- other service descriptors are closed just with close_service_fd,
> but seem not to emit such warnings -- I've run the session00 test that generates 
> helpers and haven't found any errors like that.

Ah, of course. All other close_service_fd-s are not called by helpers :)
The restore_one_task() switches the task state and only the code run by
alive and stopped has these closes.

Can you check whether moving the close for cgyard somewhere inside e.g.
close_old_fds helps?

Thanks,
Pavel