On 21/02/11 12:40 -0800, Sukadev Bhattiprolu wrote: > Louis Rilling [Louis.Rilling@xxxxxxxxxxx] wrote: > | > But in 2.6.32 i.e RHEL5, tsk->signal is set to NULL in __exit_signal(). > | > So, I am trying to rule out the following scenario: > | > > | > Child (may not be a ghost) Parent > | > ------------------------- ------ > | > - exit_notify(): is EXIT_DEAD > | > - release_task(): > | > - drops task_list_lock > | > - itself proceeds to exit. > | > - enters release_task() > | > - sets own->signal = NULL > | > (in 2.6.32, __exit_signal()) > | > > | > - enters exit_checkpoint() > | > - __wake_up_parent() > | > access parents->signal NULL ptr > | > > | > Not sure if holding task_list_lock here is needed or will help. > | > | Giving my 2 cents since I've been Cc'ed. > > Thanks, appreciate the input :-) > > | > | AFAICS, holding tasklist_lock prevents __exit_signal() from setting > | parent->signal to NULL in your back. So something like this should be safe: > | > | read_lock(&tasklist_lock); > | if (current->parent->signal) > | __wake_up_parent(...); > | read_unlock(&tasklist_lock); > > Yes, checking the parent->signal with task_list_lock would work. > > | > | I haven't looked at the context, but of course this also requires that some > | get_task_struct() on current->parent has been done somewhere else before current > | has passed __exit_signal(). > | > | By the way, instead of checking current->parent->signal, > | current->parent->exit_state would look cleaner to me. current->parent is not > | supposed to wait on ->wait_chldexit after calling do_exit(), right? > ^^^^^^^ > > Hmm, do you mean exit_notify() here ? Right, I had forgotten zap_pid_ns_processes() ;) My point was just that once ->exit_state is set (for all threads), ->signal->wait_chldexit is not used anymore. But I'm sure that you got it right :) Thanks, Louis > > If so, yes checking the exit_state is cleaner. > > If the parent's exit_state is set, then it can't be waiting for the ghost, > so no need to wake_up_parent(). If exit state is not set, then it is safe > to wake_up_parent() (parent->signal would not yet have been cleared for > instance). > > The one case where a parent in do_exit() could still wait for the child is > the container-init which waits on wait_chldexit in do_exit() -> > zap_pid_ns_processes() - but even in that case the __wake_up_parent() > call would be safe. > > Sukadev > _______________________________________________ > Containers mailing list > Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx > https://lists.linux-foundation.org/mailman/listinfo/containers -- 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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