Re: [PATCH] generic/446: make sure all background processes are dead before umount

[Eryu Guan <eguan@redhat.com>]

On Tue, Jul 25, 2017 at 09:39:28AM +0800, Xiao Yang wrote:
> On 2017/07/24 18:11, Eryu Guan wrote:
> > The $dread_pid refers to the while-true-do loop, wait for $dread_pid
> > doesn't mean the xfs_io direct read process is already dead,
> > sometimes xfs_io process is still running and blocking
> > _scratch_unmount.
> Hi Eryu,
> 
> Could you tell me what can i do to trigger this block?

I don't have a reliable reproducer, I hit this in my automated tests,
perhaps easier to hit with slow disks. You can try replace the fpunch
operation with a pwrite, I can hit the block much easier this way.

> > Fix it by making the direct read does a fixed number of loop and
> > break out the second mmap-fpunch loop if the first loop exits. At
> 
> Does it break out the second mmap-fpunch loop if the first loop doesn't
> exit?

The second mmap-fpunch loop won't break until it finds the first loop
exits.

> 
> > this point we're sure that there's no unfinished background process
> > blocking the umount.
> 
> The others look fine.

Thanks!

Eryu

> 
> Thanks,
> Xiao Yang.
> > Signed-off-by: Eryu Guan <eguan@redhat.com>
> > ---
> >  tests/generic/446 | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> >
> > diff --git a/tests/generic/446 b/tests/generic/446
> > index 62ae449de6b1..83ff4ac9edd3 100755
> > --- a/tests/generic/446
> > +++ b/tests/generic/446
> > @@ -61,20 +61,22 @@ filesz=$((65536 * 2))
> >  $XFS_IO_PROG -f -c "truncate $((filesz * 2))" $SCRATCH_MNT/file >> $seqres.full
> >  
> >  # run a background dio read to a hole in a loop
> > -while true; do
> > +for i in `seq 0 999`; do
> >  	$XFS_IO_PROG -d -c "pread 0 $filesz" $SCRATCH_MNT/file > /dev/null 2>&1
> >  done &
> >  
> >  dread_pid=$!
> >  
> >  # run mapped write to the same hole as dio read
> > -for i in `seq 0 999`; do
> > +while true; do
> >  	$XFS_IO_PROG -c "mmap 0 $filesz" -c "mwrite 0 $filesz" $SCRATCH_MNT/file \
> >  		> /dev/null
> >  	$XFS_IO_PROG -c "fpunch 0 $filesz" $SCRATCH_MNT/file > /dev/null
> > +	if ! kill -s 0 $dread_pid >/dev/null 2>&1; then
> > +		break
> > +	fi
> >  done
> >  
> > -kill -9 $dread_pid > /dev/null 2>&1
> >  wait $dread_pid > /dev/null 2>&1
> >  
> >  echo "Silence is golden"
> 
> 
>