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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: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
Oleg Nesterov 2006-03-28 16:10:59 -08:00 committed by Linus Torvalds
parent fef23e7fbb
commit 1434261c07
1 changed files with 10 additions and 12 deletions
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22
fs/exec.c
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@ -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();