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Commit 950bbabb authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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pid_ns: (BUG 11391) change ->child_reaper when init->group_leader exits 

We don't change pid_ns->child_reaper when the main thread of the
subnamespace init exits.  As Robert Rex <robert.rex@exasol.com> pointed
out this is wrong.

Yes, the re-parenting itself works correctly, but if the reparented task
exits it needs ->parent->nsproxy->pid_ns in do_notify_parent(), and if the
main thread is zombie its ->nsproxy was already cleared by
exit_task_namespaces().

Introduce the new function, find_new_reaper(), which finds the new
->parent for the re-parenting and changes ->child_reaper if needed.  Kill
the now unneeded exit_child_reaper().

Also move the changing of ->child_reaper from zap_pid_ns_processes() to
find_new_reaper(), this consolidates the games with ->child_reaper and
makes it stable under tasklist_lock.

Addresses http://bugzilla.kernel.org/show_bug.cgi?id=11391



Reported-by: default avatarRobert Rex <robert.rex@exasol.com>
Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatarSerge Hallyn <serue@us.ibm.com>
Acked-by: default avatarPavel Emelyanov <xemul@openvz.org>
Acked-by: default avatarSukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent add0d4df

kernel/exit.c

+34 −44
Original line number Diff line number Diff line
@@ -831,26 +831,50 @@ static void reparent_thread(struct task_struct *p, struct task_struct *father) 
 * the child reaper process (ie "init") in our pid

 * space.

 */

static struct task_struct *find_new_reaper(struct task_struct *father)

{

	struct pid_namespace *pid_ns = task_active_pid_ns(father);

	struct task_struct *thread;



	thread = father;

	while_each_thread(father, thread) {

		if (thread->flags & PF_EXITING)

			continue;

		if (unlikely(pid_ns->child_reaper == father))

			pid_ns->child_reaper = thread;

		return thread;

	}



	if (unlikely(pid_ns->child_reaper == father)) {

		write_unlock_irq(&tasklist_lock);

		if (unlikely(pid_ns == &init_pid_ns))

			panic("Attempted to kill init!");



		zap_pid_ns_processes(pid_ns);

		write_lock_irq(&tasklist_lock);

		/*

		 * 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;

	}



	return pid_ns->child_reaper;

}



static void forget_original_parent(struct task_struct *father)

{

	struct task_struct *p, *n, *reaper = father;

	struct task_struct *p, *n, *reaper;

	LIST_HEAD(ptrace_dead);



	write_lock_irq(&tasklist_lock);



	reaper = find_new_reaper(father);

	/*

	 * First clean up ptrace if we were using it.

	 */

	ptrace_exit(father, &ptrace_dead);



	do {

		reaper = next_thread(reaper);

		if (reaper == father) {

			reaper = task_child_reaper(father);

			break;

		}

	} while (reaper->flags & PF_EXITING);



	list_for_each_entry_safe(p, n, &father->children, sibling) {

		p->real_parent = reaper;

		if (p->parent == father) {
@@ -959,39 +983,6 @@ static void check_stack_usage(void) 
static inline void check_stack_usage(void) {}

#endif



static inline void exit_child_reaper(struct task_struct *tsk)

{

	if (likely(tsk->group_leader != task_child_reaper(tsk)))

		return;



	if (tsk->nsproxy->pid_ns == &init_pid_ns)

		panic("Attempted to kill init!");



	/*

	 * @tsk is the last thread in the 'cgroup-init' and is exiting.

	 * Terminate all remaining processes in the namespace and reap them

	 * before exiting @tsk.

	 *

	 * Note that @tsk (last thread of cgroup-init) may not necessarily

	 * be the child-reaper (i.e main thread of cgroup-init) of the

	 * namespace i.e the child_reaper may have already exited.

	 *

	 * Even after a child_reaper exits, we let it inherit orphaned children,

	 * because, pid_ns->child_reaper remains valid as long as there is

	 * at least one living sub-thread in the cgroup init.



	 * This living sub-thread of the cgroup-init will be notified when

	 * a child inherited by the 'child-reaper' exits (do_notify_parent()

	 * uses __group_send_sig_info()). Further, when reaping child processes,

	 * do_wait() iterates over children of all living sub threads.



	 * i.e even though 'child_reaper' thread is listed as the parent of the

	 * orphaned children, any living sub-thread in the cgroup-init can

	 * perform the role of the child_reaper.

	 */

	zap_pid_ns_processes(tsk->nsproxy->pid_ns);

}



NORET_TYPE void do_exit(long code)

{

	struct task_struct *tsk = current;
@@ -1051,7 +1042,6 @@ NORET_TYPE void do_exit(long code) 
	}

	group_dead = atomic_dec_and_test(&tsk->signal->live);

	if (group_dead) {

		exit_child_reaper(tsk);

		hrtimer_cancel(&tsk->signal->real_timer);

		exit_itimers(tsk->signal);

	}

kernel/pid_namespace.c

+0 −6
Original line number Diff line number Diff line
@@ -179,12 +179,6 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns) 
		rc = sys_wait4(-1, NULL, __WALL, NULL);

	} while (rc != -ECHILD);



	/*

	 * 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;

}