linux-kernel - Re: [PATCH RFC md-6.16 v3 15/19] md/md-llbitmap: implement APIs to dirty bits and clear bits

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Message-ID: <20250512051722.GA1667@lst.de>
Date: Mon, 12 May 2025 07:17:22 +0200
From: Christoph Hellwig <hch@....de>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: hch@....de, xni@...hat.com, colyli@...nel.org, agk@...hat.com,
	snitzer@...nel.org, mpatocka@...hat.com, song@...nel.org,
	yukuai3@...wei.com, linux-kernel@...r.kernel.org,
	dm-devel@...ts.linux.dev, linux-raid@...r.kernel.org,
	yi.zhang@...wei.com, yangerkun@...wei.com, johnny.chenyi@...wei.com
Subject: Re: [PATCH RFC md-6.16 v3 15/19] md/md-llbitmap: implement APIs to
 dirty bits and clear bits

On Mon, May 12, 2025 at 09:19:23AM +0800, Yu Kuai wrote:
> +static void llbitmap_unplug(struct mddev *mddev, bool sync)
> +{
> +	DECLARE_COMPLETION_ONSTACK(done);
> +	struct llbitmap *llbitmap = mddev->bitmap;
> +	struct llbitmap_unplug_work unplug_work = {
> +		.llbitmap = llbitmap,
> +		.done = &done,
> +	};
> +
> +	if (!llbitmap_dirty(llbitmap))
> +		return;
> +
> +	INIT_WORK_ONSTACK(&unplug_work.work, llbitmap_unplug_fn);
> +	queue_work(md_llbitmap_unplug_wq, &unplug_work.work);
> +	wait_for_completion(&done);
> +	destroy_work_on_stack(&unplug_work.work);

Why is this deferring the work to a workqueue, but then synchronously
waits on it?