From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
Subject: Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()
Date: Wed, 29 Jun 2016 09:15:52 -0400
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To: Petr Mladek <pmladek-IBi9RG/b67k@public.gmane.org>
Cc: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>, "Paul E. McKenney" <paulmck-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Josh Triplett <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org>, Thomas Gleixner <tglx-hfZtesqFncYOwBW4kG4KsQ@public.gmane.org>, Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Jiri Kosina <jkosina-AlSwsSmVLrQ@public.gmane.org>, Borislav Petkov <bp-l3A5Bk7waGM@public.gmane.org>, Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Vlastimil Babka <vbabka-AlSwsSmVLrQ@public.gmane.org>, linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
List-Id: linux-api@vger.kernel.org

Hello,

On Wed, Jun 29, 2016 at 10:17:48AM +0200, Petr Mladek wrote:
> > Ah, okay, I don't think we need to change this.  I was suggesting to
> > simplify it by dropping the draining and just do flush from destroy.
> 
> I see. But then it does not address the original concern from Peter
> Zijlstra. He did not like that the caller was responsible for blocking
> further queueing. It still will be needed. Or did I miss something,
> please?

You can only protect against so much.  Let's say we make the worker
struct to be allocated by the user, what then prevents it prematurely
from user side?  Use-after-free is use-after-free.  If we can trivally
add some protection against it, great, but no need to contort the
design to add marginal protection.

Thanks.

-- 
tejun