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Message-ID: <20090122172312.GB27250@redhat.com>
Date: Thu, 22 Jan 2009 18:23:12 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Frederic Weisbecker <fweisbec@...il.com>
Cc: Lai Jiangshan <laijs@...fujitsu.com>, Ingo Molnar <mingo@...e.hu>,
Andrew Morton <akpm@...ux-foundation.org>,
Peter Zijlstra <peterz@...radead.org>,
Eric Dumazet <dada1@...mosbay.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] workqueue: not allow recursion run_workqueue
On 01/22, Frederic Weisbecker wrote:
>
> On Thu, Jan 22, 2009 at 05:14:24PM +0800, Lai Jiangshan wrote:
> > static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq)
> > {
> > - int active;
> > + int active = 0;
> > + struct wq_barrier barr;
> >
> > - if (cwq->thread == current) {
> > - /*
> > - * Probably keventd trying to flush its own queue. So simply run
> > - * it by hand rather than deadlocking.
> > - */
> > - run_workqueue(cwq);
> > - active = 1;
> > - } else {
> > - struct wq_barrier barr;
> > + BUG_ON(cwq->thread == current);
>
> Hi Lai,
>
> BUG_ON seems perhaps a bit too much for such case. The system
> will run in an endless loop because of a mistake that will not have
> necessarily a fatal end.
Confused. Why do you think the system will run in an endless loop?
cwq-thread will exit.
> WARN_ON should be enough (plus the warn that lockdep will raise
> too in this case).
and if cwq-thread proceeds after WARN_ON() it will be "lost" anyway
because it will sleep forever.
Not that I think BUG_ON() is much better, except it is more "loud".
As for the patch itself, I completely agree with Peter.
Oleg.
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