move exit_task_namespaces() outside of exit_notify()

exit_notify() does exit_task_namespaces() after
forget_original_parent(). This was needed to ensure that ->nsproxy
can't be cleared prematurely, an exiting child we are going to
reparent can do do_notify_parent() and use the parent's (ours) pid_ns.

However, after 32084504 "pidns: use task_active_pid_ns in
do_notify_parent" ->nsproxy != NULL is no longer needed, we rely
on task_active_pid_ns().

Move exit_task_namespaces() from exit_notify() to do_exit(), after
exit_fs() and before exit_task_work().

This solves the problem reported by Andrey, free_ipc_ns()->shm_destroy()
does fput() which needs task_work_add().

Note: this particular problem can be fixed if we change fput(), and
that change makes sense anyway. But there is another reason to move
the callsite. The original reason for exit_task_namespaces() from
the middle of exit_notify() was subtle and it has already gone away,
now this looks confusing. And this allows us do simplify exit_notify(),
we can avoid unlock/lock(tasklist) and we can use ->exit_state instead
of PF_EXITING in forget_original_parent().

Reported-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/kernel/exit.c b/kernel/exit.c
index af2eb3cbd499305c3d418c7f8280c2d7f0f9437d..7bb73f9d09dbeedcc6c07f6a8dc8257f76fc4963 100644 (file)
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -649,7 +649,6 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
         *      jobs, send them a SIGHUP and then a SIGCONT.  (POSIX 3.2.2.2)
         */
        forget_original_parent(tsk);
-       exit_task_namespaces(tsk);
 
        write_lock_irq(&tasklist_lock);
        if (group_dead)
@@ -795,6 +794,7 @@ void do_exit(long code)
        exit_shm(tsk);
        exit_files(tsk);
        exit_fs(tsk);
+       exit_task_namespaces(tsk);
        exit_task_work(tsk);
        check_stack_usage();
        exit_thread();