From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oren Laadan Subject: Re: [PATCH][usercr]: Ghost tasks must be detached Date: Sat, 05 Feb 2011 17:02:51 -0500 Message-ID: <4D4DC90B.3010103@cs.columbia.edu> References: <20101211033548.GA12584@us.ibm.com> <4D2BB78A.9090701@cs.columbia.edu> <4D4D9D1B.3000209@cs.columbia.edu> <20110205214032.GA12944@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20110205214032.GA12944-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Sukadev Bhattiprolu Cc: Containers List-Id: containers.vger.kernel.org On 02/05/2011 04:40 PM, Sukadev Bhattiprolu wrote: > Oren Laadan [orenl-eQaUEPhvms7ENvBUuze7eA@public.gmane.org] 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 ? > > 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. If we need it and it isn't in mainline (any reason why ?) then we can just add it to our linux-cr tree, as a preparatory patch. > > Was there another change to 2.6.37 that would prevent the crash ? I don't know whether *that* crash still happens in 2.6.37 - because I still didn't test it with that kernel line back. (Actually, I never experienced that crash here even with earlier kernels). > > | (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. I'm currently chasing down a bug that causes restart to hang when there are ghost/dead tasks. It may be the same one you are seeing. So far I'm convinced it's userspace - working on it. Will post patches once solved. Thanks, Oren. > > | > | 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 > | >> 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 > | >> --- > | >> 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-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org > | > https://lists.linux-foundation.org/mailman/listinfo/containers > | > >