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Commit 84eb646b authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

handle the multi-threaded init's exit() properly 



With or without this patch, multi-threaded init's are not fully supported,
but do_exit() is completely wrong.  This becomes a real problem when we
support pid namespaces.

1. do_exit() panics when the main thread of /sbin/init exits. It should not
   until the whole thread group exits. Move the code below, under the
   "if (group_dead)" check.

   Note: this means that forget_original_parent() can use an already dead
   child_reaper()'s task_struct. This is OK for /sbin/init because

   	- do_wait() from alive sub-thread still can reap a zombie, we iterate
   	  over all sub-thread's ->children lists

   	- do_notify_parent() will wakeup some alive sub-thread because it sends
   	  the group-wide signal

   However, we should remove choose_new_parent()->BUG_ON(reaper->exit_state)
   for this.

2. We are playing games with ->nsproxy->pid_ns. This code is bogus today, and
   it has to be changed anyway when we really support pid namespaces, just
   remove it.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Roland McGrath <roland@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8e9073ed

kernel/exit.c

+11 −20
Original line number Diff line number Diff line
@@ -592,17 +592,6 @@ static void exit_mm(struct task_struct * tsk) 
	mmput(mm);

}



static inline void

choose_new_parent(struct task_struct *p, struct task_struct *reaper)

{

	/*

	 * Make sure we're not reparenting to ourselves and that

	 * the parent is not a zombie.

	 */

	BUG_ON(p == reaper || reaper->exit_state);

	p->real_parent = reaper;

}



static void

reparent_thread(struct task_struct *p, struct task_struct *father, int traced)

{
@@ -710,7 +699,7 @@ forget_original_parent(struct task_struct *father, struct list_head *to_release) 


		if (father == p->real_parent) {

			/* reparent with a reaper, real father it's us */

			choose_new_parent(p, reaper);

			p->real_parent = reaper;

			reparent_thread(p, father, 0);

		} else {

			/* reparent ptraced task to its real parent */
@@ -731,7 +720,7 @@ forget_original_parent(struct task_struct *father, struct list_head *to_release) 
	}

	list_for_each_safe(_p, _n, &father->ptrace_children) {

		p = list_entry(_p, struct task_struct, ptrace_list);

		choose_new_parent(p, reaper);

		p->real_parent = reaper;

		reparent_thread(p, father, 1);

	}

}
@@ -882,6 +871,14 @@ 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 != child_reaper(tsk)))

		return;



	panic("Attempted to kill init!");

}



fastcall NORET_TYPE void do_exit(long code)

{

	struct task_struct *tsk = current;
@@ -895,13 +892,6 @@ fastcall NORET_TYPE void do_exit(long code) 
		panic("Aiee, killing interrupt handler!");

	if (unlikely(!tsk->pid))

		panic("Attempted to kill the idle task!");

	if (unlikely(tsk == child_reaper(tsk))) {

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

			tsk->nsproxy->pid_ns->child_reaper = init_pid_ns.child_reaper;

		else

			panic("Attempted to kill init!");

	}





	if (unlikely(current->ptrace & PT_TRACE_EXIT)) {

		current->ptrace_message = code;
@@ -951,6 +941,7 @@ fastcall 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);

	}