linux-kernel - Re: [PATCH 2/3] Fix fsync livelock

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Message-ID: <20081006025116.GA12509@disturbed>
Date:	Mon, 6 Oct 2008 13:51:16 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Arjan van de Ven <arjan@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, agk@...hat.com, mbroz@...hat.com,
	chris@...chsys.com
Subject: Re: [PATCH 2/3] Fix fsync livelock

On Sun, Oct 05, 2008 at 08:01:46PM -0400, Mikulas Patocka wrote:
> This looks madly complicated. And ineffective, because if some page was 
> submitted before fsync() was invoked, and is under writeback while fsync() 
> is called, fsync() still has to wait on it.

fsync() waiting on pre-issued writeback pages is the correct
behaviour.

IOW, if the page is under writeback at the time an fsync() is
issued (e.g. issued by pdflush), the page was *not clean* at the
time the fsync() was called and hence must be clean when fsync()
returns. fsync() needs to wait for all pages under I/O at the time
it is called, not just the dirty pages it issues I/O on.....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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