linux-kernel - Re: [PATCH] workqueues: insert_work: use "list

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Message-ID: <20080612165550.GA12183@tv-sign.ru>
Date:	Thu, 12 Jun 2008 20:55:50 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jarek Poplawski <jarkao2@...pl>,
	Max Krasnyansky <maxk@...lcomm.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueues: insert_work: use "list_head *" instead of "int tail"

On 06/12, Oleg Nesterov wrote:
>
> insert_work() inserts the new work_struct before or after cwq->worklist,
> depending on the "int tail" parameter. Change it to accept "list_head *"
> instead, this shrinks .text a bit and allows us to insert the barrier
> after specific work_struct.

This allows us to implement

	int flush_work(struct work_struct *work)
	{
		struct cpu_workqueue_struct *cwq;
		struct list_head *head;
		struct wq_barrier barr;

		cwq = get_wq_data(work);
		if (!cwq)
			return 0;

		head = NULL;
		spin_lock_irq(&cwq->lock);
		if (!list_empty(&work->entry)) {
			smp_rmb();
			/*
			 * ---- FAT COMMENT ----
			 */
			if (cwq == get_wq_data(work))
				head = work->entry.next;
		} else if (cwq->current_work == work) {
			head = cwq->worklist.next;
		}

		if (head)
			insert_wq_barrier(cwq, &barr, head);
		spin_unlock_irq(&cwq->lock);

		if (!head)
			return 0;
		wait_for_completion(&barr.done);
		return 1;
	}

suggested by Peter. It only waits for selected work_struct.

I doubt it will have a lot of users though. In most cases we need
cancel_work_sync() and nothing more.

Oleg.

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