linux-kernel - Re: [PATCH, RFC rc1-mm1] implement flush

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Message-Id: <20061218165119.8cd8e7e4.akpm@osdl.org>
Date:	Mon, 18 Dec 2006 16:51:19 -0800
From:	Andrew Morton <akpm@...l.org>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	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
Subject: Re: [PATCH, RFC rc1-mm1] implement flush_work()

On Mon, 18 Dec 2006 23:17:14 +0300
Oleg Nesterov <oleg@...sign.ru> wrote:

> Add ->current_work to the "struct cpu_workqueue_struct", it points to
> currently running "struct queue_work". When flush_work(work) detects
> ->current_work == work, it inserts a barrier at the _head_ of ->worklist
> (and thus right _after_ that work) and waits for completition. This means
> that the next work fired on that CPU will be this barrier, or another
> barrier queued by concurrent flush_work(), so the caller of flush_work()
> will be woken before any "regular" work has a chance to run.
> 
> Since __queue_work() does both set_wq_data() and list_add_tail() atomically
> under cwq->lock, flush_work() can remove the pending work from queue when
> it sees "get_wq_data(work) == cwq".

Seems sane.

> NOTE: flush_work() doesn't like no-auto-release works. Unless they go away
> we can fix this later or add the "don't do this" comment.

Yes, let's make the _NAR stuff go away pleeeeze.  It's fairly
straightforward, and is on my todo list somewhere.
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