Re: [PATCH 2/3] workqueue: not allow recursion run_workqueue

From: Peter Zijlstra <peterz@infradead.org>
To: "Frédéric Weisbecker" <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>, Lai Jiangshan <laijs@cn.fujitsu.com>,
	Oleg Nesterov <oleg@tv-sign.ru>,
	Andrew Morton <akpm@linux-foundation.org>,
	Eric Dumazet <dada1@cosmosbay.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/3] workqueue: not allow recursion run_workqueue
Date: Thu, 22 Jan 2009 12:10:15 +0100	[thread overview]
Message-ID: <1232622615.4890.114.camel@laptop> (raw)
In-Reply-To: <c62985530901220306p78ea541cs28912a844297b304@mail.gmail.com>

On Thu, 2009-01-22 at 12:06 +0100, Frédéric Weisbecker wrote:

> Ok.
> Oh but I haven't seen that Oleg said he prefered bug_on, because the
> system will deadlock instead....hmm...
> 
> Or perhaps keeping the things like the old way, but with a WARN_ONCE:
> 
> if (cwq->thread == current) {
>                /*
>                 * Don't ever think to flush workqueue from a work
>                 */
>                WARN_ONCE(1);
> 
>                run_workqueue(cwq);
>                active = 1;
> }
> 
> And then, the workqueue will flush...so it will behave correctly but
> will warn on this bad developer idea of flushing from a work.

lockdep already yells at you for doing that, and developers should run
with lockdep enabled -- or at least test stuff with lockdep enabled, so
I'm not exactly seeing what this will buy us.

> Actually I don't understand when Lai says that it will actually not flush.

Yeah, his changelog is an utter mistery to many..