linux-kernel - Re: [PATCH 09/10] ptrace: add JOBCTL_BLOCK

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Message-ID: <20110519163233.GE17265@redhat.com>
Date:	Thu, 19 May 2011 18:32:33 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	jan.kratochvil@...hat.com, vda.linux@...glemail.com,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, indan@....nu, bdonlan@...il.com
Subject: Re: [PATCH 09/10] ptrace: add JOBCTL_BLOCK_NOTIFY

On 05/16, Tejun Heo wrote:
>
> +static void ptrace_put_task_struct(struct task_struct *child)
> +{
> +	unsigned long flags;
> +
> +	if (!(child->jobctl & JOBCTL_BLOCK_NOTIFY))
> +		goto out_put;
> +
> +	if (unlikely(!lock_task_sighand(child, &flags)))
> +		goto out_put;
> +
> +	/*
> +	 * Make sure @chlid is still ptraced by us and clear BLOCK_NOTIFY.
> +	 */
> +	if (likely((child->ptrace & PT_PTRACED) && child->parent == current))

This looks a bit confusing... It is either traced or not. If it is traced,
nobody else can trace it. In fact even PT_PTRACED is not strictly needed
but I agree this check makes the code cleaner.

Oleg.

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