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Date:   Fri, 19 Jul 2019 18:14:05 +0200
From:   Oleg Nesterov <oleg@redhat.com>
To:     "Joel Fernandes (Google)" <joel@joelfernandes.org>
Cc:     linux-kernel@vger.kernel.org,
        Suren Baghdasaryan <surenb@google.com>,
        kernel-team@android.com, Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christian Brauner <christian@brauner.io>,
        "Eric W. Biederman" <ebiederm@xmission.com>,
        Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH RFC v1] pidfd: fix a race in setting exit_state for pidfd
 polling
Message-ID: <20190719161404.GA24170@redhat.com>
References: <20190717172100.261204-1-joel@joelfernandes.org>
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it seems that I missed something else...

On 07/17, Joel Fernandes (Google) wrote:
>
> @@ -1156,10 +1157,11 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
>  		ptrace_unlink(p);
>  
>  		/* If parent wants a zombie, don't release it now */
> -		state = EXIT_ZOMBIE;
> +		p->exit_state = EXIT_ZOMBIE;
>  		if (do_notify_parent(p, p->exit_signal))
> -			state = EXIT_DEAD;
> -		p->exit_state = state;
> +			p->exit_state = EXIT_DEAD;
> +
> +		state = p->exit_state;
>  		write_unlock_irq(&tasklist_lock);

why do you think we also need to change wait_task_zombie() ?

pidfd_poll() only needs the exit_state != 0 check, we know that it
is not zero at this point. Why do we need to change exit_state before
do_notify_parent() ?

Oleg.