Messages in this thread Patch in this message | | | Date | Sun, 24 Aug 2008 19:49:11 +0400 | From | Oleg Nesterov <> | Subject | [PATCH 1/4] pid_ns: zap_pid_ns_processes: fix the ->child_reaper changing |
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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>
--- 2.6.27-rc4/kernel/pid_namespace.c~1_ZAP_DONT_CLEAR_REAPER 2008-07-30 13:12:49.000000000 +0400 +++ 2.6.27-rc4/kernel/pid_namespace.c 2008-08-24 17:22:59.000000000 +0400 @@ -179,9 +179,12 @@ void zap_pid_ns_processes(struct pid_nam rc = sys_wait4(-1, NULL, __WALL, NULL); } while (rc != -ECHILD); - - /* Child reaper for the pid namespace is going away */ - pid_ns->child_reaper = NULL; + /* + * We can not clear ->child_reaper or leave it alone. + * There may by stealth EXIT_DEAD tasks on ->children, + * forget_original_parent() must move them somewhere. + */ + pid_ns->child_reaper = init_pid_ns.child_reaper; acct_exit_ns(pid_ns); return; }
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