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Commit 666f164f authored by Roland McGrath's avatar Roland McGrath
Browse files

fix dangling zombie when new parent ignores children 



This fixes an arcane bug that we think was a regression introduced
by commit b2b2cbc4.  When a parent
ignores SIGCHLD (or uses SA_NOCLDWAIT), its children would self-reap
but they don't if it's using ptrace on them.  When the parent thread
later exits and ceases to ptrace a child but leaves other live
threads in the parent's thread group, any zombie children are left
dangling.  The fix makes them self-reap then, as they would have
done earlier if ptrace had not been in use.

Signed-off-by: default avatarRoland McGrath <roland@redhat.com>
parent 14dd0b81

kernel/exit.c

+26 −0
Original line number Diff line number Diff line
@@ -702,6 +702,23 @@ static void exit_mm(struct task_struct * tsk) 
	mmput(mm);

}



/*

 * Return nonzero if @parent's children should reap themselves.

 *

 * Called with write_lock_irq(&tasklist_lock) held.

 */

static int ignoring_children(struct task_struct *parent)

{

	int ret;

	struct sighand_struct *psig = parent->sighand;

	unsigned long flags;

	spin_lock_irqsave(&psig->siglock, flags);

	ret = (psig->action[SIGCHLD-1].sa.sa_handler == SIG_IGN ||

	       (psig->action[SIGCHLD-1].sa.sa_flags & SA_NOCLDWAIT));

	spin_unlock_irqrestore(&psig->siglock, flags);

	return ret;

}



/*

 * Detach all tasks we were using ptrace on.

 * Any that need to be release_task'd are put on the @dead list.
@@ -711,6 +728,7 @@ static void exit_mm(struct task_struct * tsk) 
static void ptrace_exit(struct task_struct *parent, struct list_head *dead)

{

	struct task_struct *p, *n;

	int ign = -1;



	list_for_each_entry_safe(p, n, &parent->ptraced, ptrace_entry) {

		__ptrace_unlink(p);
@@ -726,10 +744,18 @@ static void ptrace_exit(struct task_struct *parent, struct list_head *dead) 
		 * release_task() here because we already hold tasklist_lock.

		 *

		 * If it's our own child, there is no notification to do.

		 * But if our normal children self-reap, then this child

		 * was prevented by ptrace and we must reap it now.

		 */

		if (!task_detached(p) && thread_group_empty(p)) {

			if (!same_thread_group(p->real_parent, parent))

				do_notify_parent(p, p->exit_signal);

			else {

				if (ign < 0)

					ign = ignoring_children(parent);

				if (ign)

					p->exit_signal = -1;

			}

		}



		if (task_detached(p)) {