linux-kernel - Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist

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Date:	Tue, 9 Jan 2007 19:56:55 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	Andrew Morton <akpm@...l.org>, 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] flush_cpu_workqueue: don't flush an empty ->worklist

On 01/09, Srivatsa Vaddagiri wrote:
>
> On Tue, Jan 09, 2007 at 07:38:15PM +0300, Oleg Nesterov wrote:
> > We can't do this. We should thaw cwq->thread (which was bound to the
> > dead CPU) to complete CPU_DEAD event. So we still need some changes.
> 
> I noticed that, but I presumed kthread_stop() will post a wakeup which
> will bring it out of frozen state. Looking at refrigerator(), I realize
> that is not possible. 
> 
> So CPU_DEAD should do a thaw_process on the kthread before doing a
> kthread_stop?

Probably we can do this, or that. In any case we need changes, that
was my point.

And the best change I believe is to _remove_ CPU_DEAD handling from
workqueue.c as I suggested before. This kthread_stop() is not a good
idea per se, it calls wake_up_process(), but we should in fact use
wake_up(&cwq->more_work). Yes, work->func() should be ready for the
false wakeups, but still.

But for now I hope the last "draft" patch is enough. I'll continue
on next weekend.

Oleg.

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