Home » Mailing lists » Devel » Re: [PATCH][usercr]: Ghost tasks must be detached
| Re: [PATCH][usercr]: Ghost tasks must be detached [message #41596 is a reply to message #41595] |
Wed, 09 February 2011 12:37   |
Louis Rilling
Messages: 7
Registered: February 2011
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Junior Member |
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Oops, failed to add Eric properly in Cc...
Louis
On 09/02/11 13:35 +0100, Louis Rilling wrote:
> On 09/02/11 7:18 -0500, Oren Laadan wrote:
> >
> >
> > On 02/09/2011 07:01 AM, Louis Rilling wrote:
> > > On 08/02/11 18:09 -0800, Sukadev Bhattiprolu wrote:
> > >> Oren Laadan [orenl@cs.columbia.edu] wrote:
> > >> |
> > >> |
> > >> | On 02/05/2011 04:40 PM, Sukadev Bhattiprolu wrote:
> > >> | > Oren Laadan [orenl@cs.columbia.edu] wrote:
> > >> | > | Suka,
> > >> | > |
> > >> | > | This patch - and the corresponding kernel patch - are wrong
> > >> | >
> > >> | > Ah, I see that now.
> > >> | >
> > >> | > But am not sure about the kernel part though. We were getting a crash
> > >> | > reliably (with older kernels) because of the ->exit_signal = -1 in
> > >> | > do_ghost_task().
> > >> |
> > >> | Are we still getting it with 2.6.37 ?
> > >>
> > >> I am not currently getting the crash on 2.6.37 - I thought it was due to
> > >> the following commit which removed the check for task_detached() in
> > >> do_wait_thread().
> > >>
> > >> commit 9cd80bbb07fcd6d4d037fad4297496d3b132ac6b
> > >> Author: Oleg Nesterov <oleg@redhat.com>
> > >> Date: Thu Dec 17 15:27:15 2009 -0800
> > >
> > > I don't think that this introduced the bug. The bug triggers with EXIT_DEAD
> > > tasks, for which wait() must ignore (see below). So, the bug looks still there
> > > in 2.6.37.
> > >
> > >>
> > >> But if that is true, I need to investigate why Louis Rilling was getting
> > >> the crash in Jun 2010 - which he tried to fix here:
> > >>
> > >> http://lkml.org/lkml/2010/6/16/295
> > >
> > > I was getting the crash on Kerrighed, which heavily patches the 2.6.30 kernel.
> > > I could reproduce it on vanilla Linux of the moment (2.6.35-rc3), but
> > > only after introducing artificial delays in release_task().
> > >
> > > IIRC, what triggers the crash is some exiting detached task in the
> > > pid_namespace, which goes EXIT_DEAD, and as such cannot be reaped by
> > > zap_pid_ns_processes()->sys_wait4(). So with some odd timing, the detached
> > > task can call proc_flush_task() after container init does, which triggers the
> > > proc_mnt crash.
> > >
> > > Container init Some detached task in the ctnr
> > > exit_notify()
> > > ->exit_state = EXIT_DEAD
> > > exit_notify()
> > > forget_original_parent()
> > > find_new_reaper()
> > > zap_pid_ns_processes()
> > > sys_wait4()
> > > /* cannot reap EXIT_DEAD tasks */
> > > /* reparents EXIT_DEAD tasks to global init */
> > >
> > > Container reaper
> > > release_task()
> > > proc_flush_task()
> > > pid_ns_release_proc()
> > > release_task()
> > > proc_flush_task()
> > > proc_flush_task_mnt()
> > > KABOOM
> >
> > Louis, thanks for the explanation, and two follow-up questions:
> >
> > 1) Is there a patch circulating for this ? or even better, on the
> > way to mainline ?
>
> We finally agreed on a patch from Eric, but for some unknown reason, it has not
> been finalized(?) and routed to mainline yet.
>
> https://lkml.org/lkml/2010/7/12/213
>
> >
> > 2) Would it suffice if the c/r code ensures that the init never
> > exits before any EXIT_DEAD tasks ?
>
> That's what Eric's patch does: make zap_pid_ns_processes() wait until all other
> tasks (EXIT_DEAD or whatever) have passed
> release_task()->__exit_signal()->__unhash_process().
>
> Thanks,
>
> Louis
>
> --
> Dr Louis Rilling Kerlabs
> Skype: louis.rilling Batiment Germanium
> Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
> http://www.kerlabs.com/ 35700 Rennes
--
Dr Louis Rilling Kerlabs
Skype: louis.rilling Batiment Germanium
Phone: (+33|0) 6 80 89 08 23 80 avenue des Buttes de Coesmes
http://www.kerlabs.com/ 35700 Rennes
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