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

To: Stefan Behrens <sbehrens@xxxxxxxxxxxxxxxx>
Subject: Re: [PATCH 4/5] xfstests: sync before umount to avoid device busy problems
From: Lukas Czerner <lczerner@xxxxxxxxxx>
Date: Fri, 13 Apr 2012 12:57:20 +0200 (CEST)
Cc: xfs@xxxxxxxxxxx
In-reply-to: <4F87FF3D.7030803@xxxxxxxxxxxxxxxx>
References: <1334310586-2281-1-git-send-email-tmarek@xxxxxxxxxx> <1334310586-2281-4-git-send-email-tmarek@xxxxxxxxxx> <4F87FF3D.7030803@xxxxxxxxxxxxxxxx>
User-agent: Alpine 2.00 (LFD 1167 2008-08-23)
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.
> > 
> > Signed-off-by: Tom Marek <tmarek@xxxxxxxxxx>
> > 
> > Reviewed-by: Lukas Czerner <lczerner@xxxxxxxxxx>
> > ---
> >  226       |    4 ++--
> >  common.rc |    5 +++++
> >  2 files changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/226 b/226
> > index 6f28ac9..f8847c6 100755
> > --- a/226
> > +++ b/226
> > @@ -61,7 +61,7 @@ for I in `seq 1 $loops`; do
> >  done
> >  
> >  echo
> > -umount $SCRATCH_DEV
> > +_scratch_unmount
> >  _scratch_mount
> >  
> >  echo "--> $loops direct 64m writes in a loop"
> > @@ -73,7 +73,7 @@ for I in `seq 1 $loops`; do
> >  done
> >  
> >  echo
> > -umount $SCRATCH_DEV
> > +_scratch_unmount
> >  
> >  status=0
> >  exit
> > diff --git a/common.rc b/common.rc
> > index cab0b64..e56e5bc 100644
> > --- a/common.rc
> > +++ b/common.rc
> > @@ -255,6 +255,8 @@ _scratch_mount()
> >  
> >  _scratch_unmount()
> >  {
> > +    # Run sync to give processes some time to finish before unmount
> > +    sync
> >      $UMOUNT_PROG $SCRATCH_DEV
> >  }
> >  
> > @@ -1051,6 +1053,9 @@ _umount_or_remount_ro()
> >      device=$1
> >      mountpoint=`_is_mounted $device`
> >  
> > +    # Run sync to give processes some time to finish before unmount
> > +    sync
> > +
> >      if [ $USE_REMOUNT -eq 0 ]; then
> >          $UMOUNT_PROG $device
> >      else
> 
> 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.


> 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.

Thanks
-Lukas

> 
> sync before umount should never be required.
> 
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