linux-kernel - Re: [PATCH v9 06/12] kthread: Add kthread_drain

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Message-ID: <20160629131552.GA24054@htj.duckdns.org>
Date:	Wed, 29 Jun 2016 09:15:52 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Petr Mladek <pmladek@...e.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jiri Kosina <jkosina@...e.cz>, Borislav Petkov <bp@...e.de>,
	Michal Hocko <mhocko@...e.cz>, linux-mm@...ck.org,
	Vlastimil Babka <vbabka@...e.cz>, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 06/12] kthread: Add kthread_drain_worker()

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