linux-kernel - Re: [PATCH] backing_dev: Fix hung task on sync

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Message-ID: <20140219190139.GQ10134@htj.dyndns.org>
Date:	Wed, 19 Feb 2014 14:01:39 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Derek Basehore <dbasehore@...omium.org>,
	Alexander Viro <viro@...to.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Kees Cook <keescook@...omium.org>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, bleung@...omium.org, sonnyrao@...omium.org,
	semenzato@...omium.org
Subject: Re: [PATCH] backing_dev: Fix hung task on sync

Hello, Jan.

On Wed, Feb 19, 2014 at 10:27:31AM +0100, Jan Kara wrote:
>   You are the workqueue expert so you may know better ;) But the way I
> understand it is that queue_delayed_work() does nothing if the timer is
> already running. Since we queue flusher work to run either immediately or
> after dirty_writeback_interval we are safe to run queue_delayed_work()
> whenever we want it to run after dirty_writeback_interval and
> mod_delayed_work() whenever we want to run it immediately.

Ah, okay, so it's always mod on immediate and queue on delayed.  Yeah,
that should work.

> But it's subtle and some interface where we could say queue delayed work
> after no later than X would be easier to grasp.

Yeah, I think it'd be better if we had something like
mod_delayed_work_if_later().  Hmm...

Thanks.

-- 
tejun
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