Home » Mailing lists » Devel » Re: [PATCH][usercr]: Ghost tasks must be detached
| Re: [PATCH][usercr]: Ghost tasks must be detached [message #41533 is a reply to message #41531] |
Sat, 05 February 2011 21:40   |
Sukadev Bhattiprolu
Messages: 413
Registered: August 2006
|
Senior Member |
|
|
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().
One fix I was watching for was Eric Biederman's
http://lkml.org/lkml/2010/7/12/213
which AFAICT has not been merged yet.
Was there another change to 2.6.37 that would prevent the crash ?
| (I should have noticed it in the review!). It turns out that
| ghost (and dead) tasks are _not_ auto-reaped anymore.
|
| There are only two way for tasks to be auto-reaped: one is if
| their parent explicitly says so in its sighand information (but
| then it applies to all children). The other way is if they have
| ->exit_signal==-1. From userspace this happens only when cloning
| with CLONE_THREAD. Using 0xFF for the @flags argument to clone()
| syscall instead results in ->exit_signal = 255 ...
|
| The original motivation for this patch was:
|
| > The downside of marking the task detached in do_ghost_task() is that
| > with current/older kernels container-init does not wait for detached
| > tasks. See:
| >
| > http://lkml.org/lkml/2010/6/16/272
| > http://lkml.org/lkml/2010/7/12/213
| >
| > This can lead to a kernel crash if the container-init pre-deceases a
| > ghost task.
|
| Is this still a problem in 2.6.37 ?
Well, some inadvertent userspace changes seemed to cause the crash (or
an application hang on some machines) during restart. By making those changes,
I seem to be getting an application hang 5 out of 6 times even with 2.6.37,
but did not get a crash. I will investigate this new hang next week.
|
| Oren.
|
|
| On 01/10/2011 08:51 PM, Oren Laadan wrote:
| >
| > Applied to user-cr.
| >
| > Thanks,
| >
| > Oren.
| >
| > On 12/10/2010 10:35 PM, Sukadev Bhattiprolu wrote:
| >>
| >> From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
| >> Date: Fri, 10 Dec 2010 19:23:58 -0800
| >> Subject: [PATCH 1/1] Ghost tasks must be detached
| >>
| >> Ghost processes are created only to help restore orphaned sessions/pgrps.
| >> As such once the session/pgrp is created the ghost must not send another
| >> SIGCHLD to the parent but exit silently. So create such tasks as
| >> "detached".
| >>
| >> See also:
| >>
| >> https://lists.linux-foundation.org/pipermail/containers/2010 -December/026076.html
| >>
| >> Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
| >> ---
| >> restart.c | 7 +++++++
| >> 1 files changed, 7 insertions(+), 0 deletions(-)
| >>
| >> diff --git a/restart.c b/restart.c
| >> index 9fb5e9f..d7ba26b 100644
| >> --- a/restart.c
| >> +++ b/restart.c
| >> @@ -1744,6 +1744,13 @@ static pid_t ckpt_fork_child(struct ckpt_ctx *ctx, struct task *child)
| >> flags |= CLONE_THREAD | CLONE_SIGHAND | CLONE_VM;
| >> else if (child->flags & TASK_SIBLING)
| >> flags |= CLONE_PARENT;
| >> + else if (child->flags & (TASK_GHOST|TASK_DEAD)) {
| >> + /*
| >> + * Ghosts must vanish silently (without signalling parent)
| >> + * when they are done.
| >> + */
| >> + flags = 0xFF;
| >> + }
| >>
| >> memset(&clone_args, 0, sizeof(clone_args));
| >> clone_args.nr_pids = 1;
| > _______________________________________________
| > Containers mailing list
| > Containers@lists.linux-foundation.org
| > https://lists.linux-foundation.org/mailman/listinfo/containe rs
| >
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