On 02/05/2011 05:02 PM, Oren Laadan wrote: > > > On 02/05/2011 04:40 PM, Sukadev Bhattiprolu wrote: >> Oren Laadan [orenl@xxxxxxxxxxxxxxx] 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. Actually - scratch that. The bug was related to the new pids-as-objs patches to user-cr. Now, given the complexity of that patchset, I don't want to spend time on picking fixes that require backporting to the current user-cr. So let's try to focus testing and debugging efforts on kernel/user that includes those patches ? Thanks, Oren. _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
