pid_ns: zap_pid_ns_processes: fix the ->child_reaper changing
authorOleg Nesterov <oleg@tv-sign.ru>
Tue, 2 Sep 2008 21:35:48 +0000 (14:35 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Wed, 3 Sep 2008 02:21:38 +0000 (19:21 -0700)
commitadd0d4dfd660e9e4fd0af3eac3cad23583c9558f
tree8bba7c39efcd5999c0925bed083a0ca68d6a5e40
parente385ea63f44b475e034a78b6d8bc6bb50caf72ca
pid_ns: zap_pid_ns_processes: fix the ->child_reaper changing

zap_pid_ns_processes() sets pid_ns->child_reaper = NULL, this is wrong.

Yes, we have already killed all tasks in this namespace, and sys_wait4()
doesn't see any child.  But this doesn't mean ->children list is empty, we
may have EXIT_DEAD tasks which are not visible to do_wait().  In that case
the subsequent forget_original_parent() will crash the kernel because it
will try to re-parent these tasks to the NULL reaper.

Even if there are no childs, it is not good that forget_original_parent()
uses reaper == NULL.

Change the code to set ->child_reaper = init_pid_ns.child_reaper instead.
We could use pid_ns->parent->child_reaper as well, I think this does not
really matter.  These EXIT_DEAD tasks are not visible to the new ->parent
after re-parenting, they will silently do release_task() eventually.

Note that we must change ->child_reaper, otherwise
forget_original_parent() will use reaper == father, and in that case we
will hit the (correct) BUG_ON(!list_empty(&father->children)).

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
kernel/pid_namespace.c