linux-kernel - Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY

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Message-ID: <20150824145150.GA10029@mtj.duckdns.org>
Date:	Mon, 24 Aug 2015 10:51:50 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Jan Kara <jack@...e.cz>
Cc:	Dave Chinner <david@...morbit.com>, Eryu Guan <eguan@...hat.com>,
	Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	xfs@....sgi.com, axboe@...com, Jan Kara <jack@...e.com>,
	linux-fsdevel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH block/for-linus] writeback: fix syncing of I_DIRTY_TIME
 inodes

Hello, Jan.

On Mon, Aug 24, 2015 at 11:19:59AM +0200, Jan Kara wrote:
> > which shows unmount being the next writeback event queued and
> > executed after the IO completions have come in (that missed the
> > log). What is missing is the specific queue/exec events for
> > sync_sb_inodes() from the sync code for each filesystem.
> 
> Bah, I see the problem and indeed it was introduced by commit e79729123f639
> "writeback: don't issue wb_writeback_work if clean". The problem is that
> we bail out of sync_inodes_sb() if there is no dirty IO. Which is wrong
> because we have to wait for any outstanding IO (i.e. call wait_sb_inodes())
> regardless of dirty state! And that also explains why Tejun's patch fixes
> the problem because it backs out the change to the exit condition in
> sync_inodes_sb().

Dang, I'm an idiot sandwich.

> So Tejun's patch from this thread is indeed fixing the real problem but the
> comment in sync_inodes_sb() should be fixed to mention wait_sb_inodes()
> must be called in all cases... Tejun, will you fixup the comment please?

Will post an updated patch.  Kudos to Eryu and Dave for chasing it
down.

Thanks a lot.

-- 
tejun
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