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

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Message-ID: <20061123092805.1408b0c6@frecb000686>
Date:	Thu, 23 Nov 2006 09:28:05 +0100
From:	Sébastien Dugué <sebastien.dugue@...l.net>
To:	Andrew Morton <akpm@...l.org>
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 Tue, 21 Nov 2006 17:02:28 -0800
Andrew Morton <akpm@...l.org> wrote:

> 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;
> > +
> > +	
> > +
> > +	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.
> 

  OK. Does moving 'notify->target = target;' after the get_task_struct() will
do, or am I missing something more subtle?

  Thanks,

  Sébastien.
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