[CRIU] pstree C/R problems

[Pavel Emelyanov]

On 09/27/2012 11:59 AM, 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.
> 
> Is this a bug? Or is CRIU has a limitation right now for the root task?
> And what's your plan for this situation?

The plan is -- by default we should reject dumping a process tree if there's a session
in a tree whose leader is not taken into a dump. But there should be a special case in
crtools (Cyrill is working on it) when we explicitly dump that state and on restore
let the tree inherit any sid from crtools.

Does this decision suit you?

> I think we may also need a helper for root task, of course have other things to consider.
> 
> 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.
> 
> 
> regards.
> Huang Qiang
> 
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