Date: Thu, 4 Jan 2007 10:31:07 -0800
From: Andrew Morton <akpm@osdl.org>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Srivatsa Vaddagiri <vatsa@in.ibm.com>, David Howells <dhowells@redhat.com>,
       Christoph Hellwig <hch@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       Linus Torvalds <torvalds@osdl.org>, linux-kernel@vger.kernel.org,
       Gautham shenoy <ego@in.ibm.com>
Subject: Re: [PATCH, RFC] reimplement flush_workqueue()
Message-Id: <20070104103107.e33768d7.akpm@osdl.org>
In-Reply-To: <20070104180901.GA344@tv-sign.ru>
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On Thu, 4 Jan 2007 21:09:01 +0300
Oleg Nesterov <oleg@tv-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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