linux-kernel - Re: [PATCH -mm 4/7][AIO] - Make good

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Message-ID: <20070205120928.51dbc6a2@frecb000686>
Date:	Mon, 5 Feb 2007 12:09:28 +0100
From:	Sébastien Dugué <sebastien.dugue@...l.net>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, linux-aio <linux-aio@...ck.org>,
	Bharata B Rao <bharata@...ibm.com>,
	Christoph Hellwig <hch@...radead.org>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Ulrich Drepper <drepper@...hat.com>,
	Zach Brown <zach.brown@...cle.com>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Benjamin LaHaise <bcrl@...ux.intel.com>,
	Jean Pierre Dion <jean-pierre.dion@...l.net>
Subject: Re: [PATCH -mm 4/7][AIO] - Make good_sigevent() non-static


  Hi Oleg,

  thanks for your comments.

On Fri, 2 Feb 2007 21:00:39 +0300 Oleg Nesterov <oleg@...sign.ru> wrote:

> On 02/01, S?bastien Dugu? wrote:
> > 
> > +struct task_struct * sigevent_find_task(sigevent_t * event)
> > +{
> > +	struct task_struct *task = NULL;
> > +
> > +	if (event->sigev_signo <= 0 || event->sigev_signo > SIGRTMAX)
> > +		return NULL;
> > +
> > +	if ((event->sigev_notify & SIGEV_THREAD_ID ) == SIGEV_THREAD_ID) {
> > +		task = find_task_by_pid(event->sigev_notify_thread_id);
> > +
> > +		if (!task || task->tgid != current->tgid)
> > +			task = NULL;
> > +	} else if (event->sigev_notify == SIGEV_SIGNAL)
> > +		task = current->group_leader;
> > +
> > +	return task;
> > +}
> 
> I am afraid this is still not right. Consider
> 
> 	->sigev_notify == SIGEV_THREAD_ID | RANDOM_BIT
> 
> Now, the second "if (SIGEV_THREAD_ID)" returns a valid task. However,
> 
> 	really_put_req:
> 
> 		if (notify == SIGEV_THREAD_ID || notify == SIGEV_SIGNAL)
> 			put_task_struct();
> 
> doesn't work, so we have task_struct leak.

  Right, I'll revert back to the old code with cleanups.

> 
> Worse, this breaks posix-timers. Note that posix-timers allow SIGEV_NONE,
> the timer is not queued in that case, we shouldn't do ->sigev_signo check.
> This means that aio should check SIGEV_NONE itself.
> 
> Also, it is critical for posix-timers that SIGEV_THREAD_ID doesn't come
> with another bit (like in the example below), note the code like
> 
> 	if (sigev_notify == (SIGEV_SIGNAL|SIGEV_THREAD_ID))
> 		...
> 
> IOW: good_sigevent() in its current form is very cryptic, and it _really_
> needs a cleanup, but we should not change its behaviour.

  Yep. I must admit that I didn't pay enough attention to this 10-liner,
but in the end it rightfully backfired on me.

> 
> Apart from this, I don't see other problems in the signal related code in
> this series.
> 
> Oleg.
> 

  Thanks again for your review.

  Sébastien.
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