Re: [BULK] Re: [PATCH] xfstests 311: test fsync with dm flakey V2

[Dave Chinner <david@fromorbit.com>]

On Thu, Apr 25, 2013 at 09:32:37PM -0400, Josef Bacik wrote:
> On Thu, Apr 25, 2013 at 07:08:29PM -0600, Dave Chinner wrote:
> > On Thu, Apr 25, 2013 at 08:24:04PM -0400, Josef Bacik wrote:
> > > On Thu, Apr 25, 2013 at 04:45:56PM -0600, Dave Chinner wrote:
> > > > On Thu, Apr 25, 2013 at 10:12:56AM -0400, Josef Bacik wrote:
> > .....
> > > > > +	$here/src/fsync-tester -s $SEED -r -t $test_num $extra $testfile
> > > > > +	if [ $? -ne 0 ]; then
> > > > > +		_unmount_flakey
> > > > > +		_cleanup
> > > > > +		exit
> > > > > +	fi
> > > > > +
> > > > > +	_md5_checksum $testfile
> > > > > +	_drop_writes
> > > > > +	_unmount_flakey
> > > > 
> > > > So, _drop_writes suspends the dm-flakey device, freezes the
> > > > filesystem, turns off writes then thaws the filesystem, right?
> > > >
> > > > If so, doesn't that mean you're not actually testing fsync() as the
> > > > freeze will effectively sync the entire filesystem before you start
> > > > dropping writes?
> > > > 
> > > > I can see why you want to stop unmount from writing back metadata to
> > > > simulate a crash, but if you've already frozen the filesystem then
> > > > writeback has already occurred before you stop the writes. So I
> > > > can't see how this is actually testing fsync - what it appears to be
> > > > testing is the fileystem freeze code...
> > > > 
> > > > [ This is precisely the issue that XFS shutdown ioctls deal with to
> > > > trigger an immediate forced shutdown of the filesystem that prevents
> > > > *any* further writes from being issued by the filesystem - no sync
> > > > operations get in the way and change the state of the filesystem
> > > > after then fsync call, so we know that what is on disk is what was
> > > > written by the sync/fsync calls being tested.
> > > > 
> > > > This is how we test sync/fsync in other XFS tests (e.g.
> > > > xfs/137-140), and this is the reason why us XFS people have
> > > > suggested that other filesystems should implement the ioctls for
> > > > this functionality rather than try to invent new ways of trying
> > > > to stop filesystems from writing back dirty metadata for fsync/sync
> > > > testing....
> > > > 
> > > > Besides, if a corruption is detected, you need a method of stopping
> > > > all dirty metadata from being written back in the filesystem to
> > > > prevent propagation of the corruption.  These ioctls should just be
> > > > an interface into that mechanism. ]
> > > >
> > > 
> > > So I need to look at what this does.  I don't think it freezes the file system,
> > 
> > `dmsetup suspend` ends up in dm_suspend(). This calls lock_fs(), which
> > calls freeze_bdev()....
> > 
> > If you do `dmsetup suspend --nolockfs` then it won't freeze the
> > filesystem during the suspend...
> >
> 
> Ok so I think I'll just make this test do all the iterations of the fsync tester
> with and without --nolockfs, since without --nolockfs I'm still seeing problems,
> does that sound reasonable?

Sounds like a fine plan to me ;)

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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