[CRIU] pstree C/R problems

[Cyrill Gorcunov]

On Thu, Sep 27, 2012 at 03:59:49PM +0800, Huang Qiang wrote:
> HI:
> I use a simple code to test CRIU, when it runs, the ids seem like this:
> 
> UID        PID  PPID  PGID   SID  C STIME TTY          TIME   CMD
> root     11988  9904 11988 11988  0 10:37 ?        00:00:00     sshd: root at pts/3
> root     11996 11988 11996 11996  0 10:37 pts/3    00:00:00       -bash
> root     12056 11996 12056 11996  0 10:38 pts/3    00:00:00         ./multitask_simple
> root     12057 12056 12056 11996  0 10:38 pts/3    00:00:00           ./multitask_simple
> 
> then I run:
> # ./crtools dump -D /home/hq/image -t 12056
> it is successful.
> 
> then restore it:
> # ./crtools restore -D /home/hq/image -t 12056
> I got error:
>  12057: Error (cr-restore.c:677): Requested sid 11996 doesn't match inherited 11952
>  12056: Error (cr-restore.c:633): 12057 exited, status=1
> Error (cr-restore.c:911): Someone can't be restored
> 
> I read the pstree C/R code, and found that it didn't handle the situation that
> the root task is not the session leader. But if there is only one task in the tree,
> C/R can successful, otherwise, will face the error.

As far as I know it's expected behaviour when subtree is dumped
(see commit 1264a7a9c6d42d3bdf383082c141c08ccf5744ac).

> Is this a bug? Or is CRIU has a limitation right now for the root task?
> And what's your plan for this situation?
> I think we may also need a helper for root task, of course have other things to consider.

I can't tell for all team but as for me -- when subtree is dumped there
are a number of limitation applies and this is not a scenario which is
encouraged. So I would say we prefer when the complete tree is dumped,
still subtree dumping is allowed but with a number of limitations.

> BTW, the born_sid mechanism seems didn't do any really work for rebuild the pstree,
> but for the check. We may neither support the tree like this:
>         pid = 5
>         sid = 5
>            /
>           /
>       pid = 7
>       sid = 6
>          /
>         /
>     pid = 9
>     sid = 8
> 
> Right?
> 
> Since I didn't find any scheme for the the problems I mentioned above in the TODO
> list, if you guys have any plan or thoughts, could you share them here?
> And maybe I can help to do this work.

Lets wait for Pavel and Andrew answers.