linux-kernel - Re: [PATCH, RFC] reimplement flush

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Message-Id: <20070104103107.e33768d7.akpm@osdl.org>
Date:	Thu, 4 Jan 2007 10:31:07 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...l.org>,
	linux-kernel@...r.kernel.org, Gautham shenoy <ego@...ibm.com>
Subject: Re: [PATCH, RFC] reimplement flush_workqueue()

On Thu, 4 Jan 2007 21:09:01 +0300
Oleg Nesterov <oleg@...sign.ru> wrote:

> > --- a/kernel/workqueue.c~flush_workqueue-use-preempt_disable-to-hold-off-cpu-hotplug
> > +++ a/kernel/workqueue.c
> > @@ -419,18 +419,22 @@ static void flush_cpu_workqueue(struct c
> >  		 * Probably keventd trying to flush its own queue. So simply run
> >  		 * it by hand rather than deadlocking.
> >  		 */
> > -		mutex_unlock(&workqueue_mutex);
> > +		preempt_enable();
> 
> Ah, (looking at _cpu_down()->stop_machine()), so preempt_disable() not only "pins"
> the current CPU, it blocks cpu_down(), yes ???

yep.

But before we do much more of this we should have a wrapper.  Umm

static inline void block_cpu_hotplug(void)
{
	preempt_disable();
}

and use that, so people can see why it's being used.

I spose I'll do that and convert this patch to use it.
-
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