linux-kernel - Re: [PATCH -mm 3/4][AIO] - AIO completion signal notification

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Message-Id: <20061121170228.4412b572.akpm@osdl.org>
Date:	Tue, 21 Nov 2006 17:02:28 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Sébastien Dugué <sebastien.dugue@...l.net>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-aio <linux-aio@...ck.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Zach Brown <zach.brown@...cle.com>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Jean Pierre Dion <jean-pierre.dion@...l.net>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [PATCH -mm 3/4][AIO] - AIO completion signal notification

On Mon, 20 Nov 2006 15:22:52 +0100
S__bastien Dugu__ <sebastien.dugue@...l.net> wrote:

> +static long aio_setup_sigevent(struct aio_notify *notify,
> +			       struct sigevent __user *user_event)
> +{
> +	sigevent_t event;
> +	struct task_struct *target;
> +
> +	if (copy_from_user(&event, user_event, sizeof (event)))
> +		return -EFAULT;
> +
> +	if (event.sigev_notify == SIGEV_NONE)
> +		return 0;
> +
> +	notify->notify = event.sigev_notify;
> +	notify->signo = event.sigev_signo;
> +	notify->value = event.sigev_value;
> +
> +	read_lock(&tasklist_lock);
> +	target = good_sigevent(&event);
> +
> +	if (unlikely(!target || (target->flags & PF_EXITING)))
> +		goto out_unlock;
> +
> +	notify->target = target;
> +
> +	if (notify->notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID)) {
> +		/*
> +		 * This reference will be dropped in really_put_req() when
> +		 * we're done with the request.
> +		 */
> +		get_task_struct(target);
> +	}

It worries me that this function can save away a task_struct* without
having taken a reference against it.


> +	read_unlock(&tasklist_lock);
> +
> +	/*
> +	 * NOTE: we cannot free the sigqueue in the completion path as
> +	 * the signal may not have been delivered to the target task.
> +	 * Therefore it has to be freed in __sigqueue_free() when the
> +	 * signal is collected if si_code is SI_ASYNCIO.
> +	 */
> +	notify->sigq = sigqueue_alloc();
> +
> +	if (unlikely(!notify->sigq))
> +		return -EAGAIN;
> +
> +	return 0;
> +
> +out_unlock:
> +	read_unlock(&tasklist_lock);
> +	return -EINVAL;
> +}
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