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Commit 1434261c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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[PATCH] simplify exec from init's subthread 



I think it is enough to take tasklist_lock for reading while changing
child_reaper:

	Reparenting needs write_lock(tasklist_lock)

	Only one thread in a thread group can do exec()

	sighand->siglock garantees that get_signal_to_deliver()
	will not see a stale value of child_reaper.

This means that we can change child_reaper earlier, without calling
zap_other_threads() twice.

"child_reaper = current" is a NOOP when init does exec from main thread, we
don't care.

Signed-off-by: default avatarOleg Nesterov <oleg@tv-sign.ru>
Acked-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent fef23e7f

fs/exec.c

+10 −12
Original line number Diff line number Diff line
@@ -616,6 +616,15 @@ static int de_thread(struct task_struct *tsk) 
		kmem_cache_free(sighand_cachep, newsighand);

		return -EAGAIN;

	}



	/*

	 * child_reaper ignores SIGKILL, change it now.

	 * Reparenting needs write_lock on tasklist_lock,

	 * so it is safe to do it under read_lock.

	 */

	if (unlikely(current->group_leader == child_reaper))

		child_reaper = current;



	zap_other_threads(current);

	read_unlock(&tasklist_lock);
@@ -660,23 +669,12 @@ static int de_thread(struct task_struct *tsk) 
		struct dentry *proc_dentry1, *proc_dentry2;

		unsigned long ptrace;



		leader = current->group_leader;

		/*

		 * If our leader is the child_reaper become

		 * the child_reaper and resend SIGKILL signal.

		 */

		if (unlikely(leader == child_reaper)) {

			write_lock(&tasklist_lock);

			child_reaper = current;

			zap_other_threads(current);

			write_unlock(&tasklist_lock);

		}



		/*

		 * Wait for the thread group leader to be a zombie.

		 * It should already be zombie at this point, most

		 * of the time.

		 */

		leader = current->group_leader;

		while (leader->exit_state != EXIT_ZOMBIE)

			yield();