linux-kernel - Re: [PATCH 2/4] FUSE: make request_wait_answer() wait for ->end() completion

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Message-Id: <E1MJPJX-0001NB-SG@pomaz-ex.szeredi.hu>
Date:	Wed, 24 Jun 2009 12:02:47 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	tj@...nel.org
CC:	linux-kernel@...r.kernel.org, fuse-devel@...ts.sourceforge.net,
	miklos@...redi.hu, akpm@...ux-foundation.org, npiggin@...e.de,
	tj@...nel.org
Subject: Re: [PATCH 2/4] FUSE: make request_wait_answer() wait for ->end() completion

On Thu, 18 Jun 2009, Tejun Heo wrote:
> Previously, a request was marked FINISHED before ->end() is executed
> and thus request_wait_answer() can return before it's done.  This
> patch makes request_wait_answer() wait for ->end() to finish before
> returning.

Why is this change needed?

> 
> Note that no current ->end() user waits for request completion, so
> this change doesn't cause any behavior difference.
> 
> While at it, beef up the comment above ->end() hook and clarify when
> and where it's called.

OK.

[snip]

> @@ -293,10 +292,21 @@ __releases(&fc->lock)
>  		fc->active_background--;
>  		flush_bg_queue(fc);
>  	}
> +
>  	spin_unlock(&fc->lock);
> -	wake_up(&req->waitq);
> -	if (end)
> +
> +	if (end) {
>  		end(fc, req);
> +		smp_wmb();

Why is this barrier needed?

Thanks,
Miklos
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