linux-kernel - Re: [PATCH 1/2] exec: don't wait for zombie threads with cred_guard

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Message-ID: <20170213180131.GA2699@redhat.com>
Date:   Mon, 13 Feb 2017 19:01:31 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Mika Penttilä <mika.penttila@...tfour.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Aleksa Sarai <asarai@...e.com>,
        Andy Lutomirski <luto@...capital.net>,
        Attila Fazekas <afazekas@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Ulrich Obergfell <uobergfe@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] exec: don't wait for zombie threads with
 cred_guard_mutex held

On 02/13, Mika Penttilä wrote:
>
> > +int de_thread(struct task_struct *tsk)
> >  {
> >  	struct signal_struct *sig = tsk->signal;
> >  	struct sighand_struct *oldsighand = tsk->sighand;
> > @@ -1051,60 +1100,24 @@ static int de_thread(struct task_struct *tsk)
> >  	if (thread_group_empty(tsk))
> >  		goto no_thread_group;
> >
> > -	/*
> > -	 * Kill all other threads in the thread group.
> > -	 */
> >  	spin_lock_irq(lock);
> > -	if (signal_group_exit(sig)) {
> > -		/*
> > -		 * Another group action in progress, just
> > -		 * return so that the signal is processed.
> > -		 */
> > -		spin_unlock_irq(lock);
> > -		return -EAGAIN;
> > -	}
> > -
> > -	sig->group_exit_task = tsk;
> > -	sig->notify_count = zap_other_threads(tsk);
> > +	sig->notify_count = sig->nr_threads;
>
>
> maybe nr_threads - 1 since nr_threads includes us ?

Damn. Of course you are right, thanks a lot! Please see v2.

Hmm. I didn't even notice my own test-case didn't pass because of this
off-by-one.

Oleg.