Re: [PATCH] generic/558: avoid forkbombs on filesystems with many free inodes

["Darrick J. Wong" <djwong@kernel.org>]

On Mon, Jul 17, 2023 at 11:03:03AM +0800, Zorro Lang wrote:
> On Fri, Jul 14, 2023 at 07:59:00AM -0700, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > Mikulas reported that this test became a forkbomb on his system when he
> > tested it with bcachefs.  Unlike XFS and ext4, which have large inodes
> > consuming hundreds of bytes, bcachefs has very tiny ones.  Therefore, it
> > reports a large number of free inodes on a freshly mounted 1GB fs (~15
> > million), which causes this test to try to create 15000 processes.
> > 
> > There's really no reason to do that -- all this test wanted to do was to
> > exhaust the number of inodes as quickly as possible using all available
> > CPUs, and then it ran xfs_repair to try to reproduce a bug.  Set the
> > number of subshells to 4x the CPU count and spread the work among them
> > instead of forking thousands of processes.
> > 
> > Reported-by: Mikulas Patocka <mpatocka@redhat.com>
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > Tested-by: Mikulas Patocka <mpatocka@redhat.com>
> > ---
> >  tests/generic/558 |   18 ++++++++++++------
> >  1 file changed, 12 insertions(+), 6 deletions(-)
> > 
> > diff --git a/tests/generic/558 b/tests/generic/558
> > index 4e22ce656b..de5c28d00d 100755
> > --- a/tests/generic/558
> > +++ b/tests/generic/558
> > @@ -39,15 +39,21 @@ _scratch_mkfs_sized $((1024 * 1024 * 1024)) >>$seqres.full 2>&1
> >  _scratch_mount
> >  
> >  i=0
> > -free_inode=`_get_free_inode $SCRATCH_MNT`
> > -file_per_dir=1000
> > -loop=$((free_inode / file_per_dir + 1))
> > +free_inodes=$(_get_free_inode $SCRATCH_MNT)
> > +nr_cpus=$(( $($here/src/feature -o) * 4 * LOAD_FACTOR ))
> > +echo "free inodes: $free_inodes nr_cpus: $nr_cpus" >> $seqres.full
> > +
> > +if ((free_inodes <= nr_cpus)); then
> > +	nr_cpus=1
> > +	files_per_dir=$free_inodes
> > +else
> > +	files_per_dir=$(( (free_inodes + nr_cpus - 1) / nr_cpus ))
> > +fi
> >  mkdir -p $SCRATCH_MNT/testdir
> >  
> >  echo "Create $((loop * file_per_dir)) files in $SCRATCH_MNT/testdir" >>$seqres.full
> 
> Has the $loop been removed?

DOH.  v3 on the way.  I hate bash.

--D

> > -while [ $i -lt $loop ]; do
> > -	create_file $SCRATCH_MNT/testdir $file_per_dir $i >>$seqres.full 2>&1 &
> > -	let i=$i+1
> > +for ((i = 0; i < nr_cpus; i++)); do
> > +	create_file $SCRATCH_MNT/testdir $files_per_dir $i >>$seqres.full 2>&1 &
> >  done
> >  wait
> >  
> > 
>