linux-ext4 - RE: ext4 out of order when use cfq scheduler

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Message-ID: <c91b1f9d6ed04caa964cb60b19d972e5@SGPMBX1004.APAC.bosch.com>
Date:	Fri, 8 Jan 2016 00:46:42 +0000
From:	"HUANG Weller (CM/ESW12-CN)" <Weller.Huang@...bosch.com>
To:	Jan Kara <jack@...e.cz>
CC:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
	"Li, Michael" <huayil@....qualcomm.com>
Subject: RE: ext4 out of order when use cfq scheduler

> >
> > >
> > > OK, so I was looking into the code and indeed, reality is correct
> > > and my mental model was wrong! ;) I thought that inode gets added to
> > > the list of inodes for which we need to wait for data IO completion
> > > during transaction commit during block allocation. And I was wrong.
> > > It used to happen in
> > > mpage_da_map_and_submit() until commit f3b59291a69d (ext4: remove
> > > calls to
> > > ext4_jbd2_file_inode() from delalloc write path) where it got
> > > removed. And that was wrong because although we submit data writes
> > > before dropping handle for allocating transaction and updating
> > > i_size, nobody guarantees that data IO is not delayed in the block layer until
> transaction commit.
> > > Which seems to happen in your case. I'll send a fix. Thanks for your
> > > report and persistence!
> > >
> >
> > Thanks a lot for your feedback :-)
> > Because I am not familiar with the detail of the ext4 internal code.  I will try to
> understand your explanation which you describe above.  And have a look on
> related funcations.
> > Could you send the fix in this mail ?
> > And whether the kernel 3.14 also have such issue, right ?
> 
> The problem is in all kernels starting with 3.8. Attached is a patch which should fix
> the issue. Can you test whether it fixes the problem for you?
> 
> 								Honza
> --

Yes, of course I will redo the test with the patch. And also give you feedback.
Thanks.
Huang weller

> Jan Kara <jack@...e.com>
> SUSE Labs, CR
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