Re: [PATCH 03/10] xfs: test rtalloc alignment and math errors

[Chandan Babu R <chandanrlinux@gmail.com>]

On 23 Mar 2021 at 09:45, Darrick J. Wong wrote:
> On Thu, Mar 11, 2021 at 01:28:32PM +0530, Chandan Babu R wrote:
>> On 09 Mar 2021 at 10:10, Darrick J. Wong wrote:
>> > From: Darrick J. Wong <djwong@kernel.org>
>> >
>> > Add a couple of regression tests for "xfs: make sure the rt allocator
>> > doesn't run off the end" and "xfs: ensure that fpunch, fcollapse, and
>> > finsert operations are aligned to rt extent size".
>> >
>> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
>> > ---
>> >  tests/xfs/759     |  100 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>> >  tests/xfs/759.out |    2 +
>> >  tests/xfs/760     |   68 ++++++++++++++++++++++++++++++++++++
>> >  tests/xfs/760.out |    9 +++++
>> >  tests/xfs/group   |    2 +
>> >  5 files changed, 181 insertions(+)
>> >  create mode 100755 tests/xfs/759
>> >  create mode 100644 tests/xfs/759.out
>> >  create mode 100755 tests/xfs/760
>> >  create mode 100644 tests/xfs/760.out
>> >
>> >
>> > diff --git a/tests/xfs/759 b/tests/xfs/759
>> > new file mode 100755
>> > index 00000000..8558fe30
>> > --- /dev/null
>> > +++ b/tests/xfs/759
>> > @@ -0,0 +1,100 @@
>> > +#! /bin/bash
>> > +# SPDX-License-Identifier: GPL-2.0-or-later
>> > +# Copyright (c) 2021 Oracle.  All Rights Reserved.
>> > +#
>> > +# FS QA Test No. 759
>> > +#
>> > +# This is a regression test for commit 2a6ca4baed62 ("xfs: make sure the rt
>> > +# allocator doesn't run off the end") which fixes an overflow error in the
>> > +# _near realtime allocator.  If the rt bitmap ends exactly at the end of a
>> > +# block and the number of rt extents is large enough to allow an allocation
>> > +# request larger than the maximum extent size, it's possible that during a
>> > +# large allocation request, the allocator will fail to constrain maxlen on the
>> > +# second run through the loop, and the rt bitmap range check will run right off
>> > +# the end of the rtbitmap file.  When this happens, xfs triggers a verifier
>> > +# error and returns EFSCORRUPTED.
>> > +
>> > +seq=`basename $0`
>> > +seqres=$RESULT_DIR/$seq
>> > +echo "QA output created by $seq"
>> > +
>> > +here=`pwd`
>> > +tmp=/tmp/$$
>> > +status=1    # failure is the default!
>> > +trap "_cleanup; exit \$status" 0 1 2 3 15
>> > +
>> > +_cleanup()
>> > +{
>> > +	cd /
>> > +	rm -f $tmp.*
>> > +}
>> > +
>> > +# get standard environment, filters and checks
>> > +. ./common/rc
>> > +. ./common/filter
>> > +
>> > +# real QA test starts here
>> > +_supported_fs xfs
>> > +_require_scratch
>> > +_require_realtime
>> > +_require_test_program "punch-alternating"
>> > +
>> > +rm -f $seqres.full
>> > +
>> > +# Format filesystem to get the block size
>> > +_scratch_mkfs > $seqres.full
>> > +_scratch_mount >> $seqres.full
>> > +
>> > +blksz=$(_get_block_size $SCRATCH_MNT)
>> > +rextsize=$($XFS_INFO_PROG $SCRATCH_MNT | grep realtime.*extsz | sed -e 's/^.*extsz=\([0-9]*\).*$/\1/g')
>> > +rextblks=$((rextsize / blksz))
>> > +
>> > +echo "blksz $blksz rextsize $rextsize rextblks $rextblks" >> $seqres.full
>> > +
>> > +_scratch_unmount
>> > +
>> > +# Format filesystem with a realtime volume whose size fits the following:
>> > +# 1. Longer than (XFS MAXEXTLEN * blocksize) bytes.
>> 
>> Shouldn't the multiplier be RT extent size rather than FS block size?
>
> No, because reproducing the bug requires a large enough allocation
> request that we can't fit it all in a single data fork extent mapping
> and have to call back into the allocator to get more space.  bmbt
> mappings are always in units of fsblocks, not rt extents.
>

Ah, I had not realized that.

The changes look good to me,

Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>

-- 
chandan