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Date: Fri, 13 Mar 2015 17:21:13 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>, Ingo Molnar <mingo@redhat.com>,
        Kees Cook <keescook@chromium.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Rik van Riel <riel@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Michael Kerrisk <mtk.manpages@gmail.com>, linux-kernel@vger.kernel.org,
        linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        x86@kernel.org
Subject: Re: [PATCH 6/6] clone4: Introduce new CLONE_FD flag to get task
	exit notification via fd
Message-ID: <20150313162113.GA25966@redhat.com>
References: <cover.1426180120.git.josh@joshtriplett.org> <9c39c576e1d9a9912b4aec54d833a73a84d2f592.1426180120.git.josh@joshtriplett.org>
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Josh,

I'll certainly try to read this series, but not before next week.

but a couple of nits right now.

On 03/12, Josh Triplett wrote:
>
> When passed CLONE_FD, clone4 will return a file descriptor rather than a
> PID.  When the child process exits, it gets automatically reaped,

And even I have no idea what you are actually doing, this doesn't look
right, see below.

> +static unsigned int clonefd_poll(struct file *file, poll_table *wait)
> +{
> +	struct task_struct *p = file->private_data;
> +	poll_wait(file, &p->clonefd_wqh, wait);
> +	return p->exit_state == EXIT_DEAD ? (POLLIN | POLLRDNORM) : 0;
> +}
> +
> +static ssize_t clonefd_read(struct file *file, char __user *buf, size_t count, loff_t *ppos)
> +{
> +	struct task_struct *p = file->private_data;
> +	int ret = 0;
> +
> +	/* EOF after first read */
> +	if (*ppos)
> +		return 0;
> +
> +	if (file->f_flags & O_NONBLOCK)
> +		ret = -EAGAIN;
> +	else
> +		ret = wait_event_interruptible(p->clonefd_wqh, p->exit_state == EXIT_DEAD);
> +
> +	if (p->exit_state == EXIT_DEAD) {

Again, I simply do not know what this code does at all. But I bet the usage
of EXIT_DEAD is wrong ;)

OK, OK, I can be wrong. But I simply do not see what protects this task_struct
if it is EXIT_DEAD (in fact even if it is EXIT_ZOMBIE).

> @@ -598,7 +600,9 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
>  	if (group_dead)
>  		kill_orphaned_pgrp(tsk->group_leader, NULL);
>  
> -	if (unlikely(tsk->ptrace)) {
> +	if (tsk->autoreap) {
> +		autoreap = true;

Debuggers won't be happy. A ptraced task should not autoreap itself.

Oleg.