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Re: [PATCH 4/5] xfstests: sync before umount to avoid device busy proble

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH 4/5] xfstests: sync before umount to avoid device busy problems
From: Lukas Czerner <lczerner@xxxxxxxxxx>
Date: Mon, 16 Apr 2012 08:57:00 +0200 (CEST)
Cc: Lukas Czerner <lczerner@xxxxxxxxxx>, Stefan Behrens <sbehrens@xxxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20120413115812.GP6734@dastard>
References: <1334310586-2281-1-git-send-email-tmarek@xxxxxxxxxx> <1334310586-2281-4-git-send-email-tmarek@xxxxxxxxxx> <4F87FF3D.7030803@xxxxxxxxxxxxxxxx> <alpine.LFD.2.00.1204131249390.14961@xxxxxxxxxxxxxxxxxxxxxxxxxx> <20120413115812.GP6734@dastard>
User-agent: Alpine 2.00 (LFD 1167 2008-08-23)
On Fri, 13 Apr 2012, Dave Chinner wrote:

> On Fri, Apr 13, 2012 at 12:57:20PM +0200, Lukas Czerner wrote:
> > On Fri, 13 Apr 2012, Stefan Behrens wrote:
> > > On 4/13/2012 11:49 AM, tmarek@xxxxxxxxxx wrote:
> > > > From: Tom Marek <tmarek@xxxxxxxxxx>
> > > > 
> > > > Some tests might fail because of 'device or resource busy' when 
> > > > unmounting
> > > > either the SCRATCH or the TEST device. The reason this happenes is that
> > > > some processes might not have time to finish properly, or they are still
> > > > waiting for IO. The sync command was added before unmount into
> > > > _scratch_unmount() and umount_or_remount_ro which should help processes 
> > > > to
> > > > finish before unmounting takes place and thus it solves the problem.
> > > > This fixes for example tests 226 and 247.
> > > > 
> > > > Test 226 uses plain umount command which suffers from exactly the same 
> > > > problem
> > > > as described above. Use fixed _scratch_unmount() instead of plain 
> > > > umount fixes
> > > > this problem.
> ....
> > > 
> > > If a xfstest process is still running when _scratch_umount() is called,
> > > that xfstest is wrong and needs to be fixed IMO.
> > 
> > I agree, however some tests does not explicitly wait for all processes
> > to finish. It is kind of hard to see why 226 has this problem, since
> > there are no processes running on background, but sync certainly seems
> > to help. It seems to be just a matter of timing though.
> 
> Which indicates a problem that needs to be understood, not hidden.
> 
> > > If a system or filesystem thread is still running and umount fails to
> > > handle it, the system or filesystem needs to be fixed IMO.
> > > 
> > > xfstests shall uncover issues, not hide them.
> > 
> > I do not think this is fs issue at all.
> 
> There are no background threads in 226, so if the unmount is failing
> then there is something wrong with the unmount process.  Indeed, 226
> is doing direct Io writes prior to unmount, so the only dirty
> objects should be the inode and free space indexing metadata. If
> unmount is failing to handle this, we need to know why....
> 
> So I definitely agree with Stefan on this one - adding a sync before
> unmount looks like hiding a problem rather than solving it...

Hmm ok, you're right. Since there is no background process we have to see
what is actually holding back unmount from proceeding successfully. Tom,
will you look into this please ?

Thanks!
-Lukas

> 
> Cheers,
> 
> Dave.
> 

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