Re: [PATCH] fstests: btrfs: add a new test case to verify degraded RMW writes

[Zorro Lang <zlang@kernel.org>]

On Thu, Oct 01, 2026 at 01:40:08PM +0930, Qu Wenruo wrote:
> This is a regression test for a recent reported bug.
> 
> The test workload is pretty straightforward:
> 
> - Create a 4 disks RAID5 or RAID6 btrfs
> 
> - Destroy one disk and mount the btrfs degraded
> 
> - Use fio to do a workload meeting all the following conditions
>   * Triggering a RMW write
>     This is done by using buffered write with 8 4K writes.
>     The total write will not fulfill a full stripe, thus it will
>     always go through RMW.
> 
>   * Some blocks of the full stripe have csum and some do not
>     This is done by pre-allocating the target file before testing, so
>     every full stripe does not have any csum by default.
> 
>     Then after some writes, there will be checksum for those new writes,
>     resulting blocks with mixed data checksum.
> 
>   * Detect RMW failure
>     This is done through fdatasync.
> 
> For unpatched kernels, the fio will always fail pretty early, meanwhile
> patched kernels can finish the full 15 seconds runs on both RAID5 and
> RAID6 profiles.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---

A standard and clear test case. Acked.

Reviewed-by: Zorro Lang <zlang@kernel.org>

>  tests/btrfs/357     | 65 +++++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/357.out |  2 ++
>  2 files changed, 67 insertions(+)
>  create mode 100755 tests/btrfs/357
>  create mode 100644 tests/btrfs/357.out
> 
> diff --git a/tests/btrfs/357 b/tests/btrfs/357
> new file mode 100755
> index 00000000..f2c04285
> --- /dev/null
> +++ b/tests/btrfs/357
> @@ -0,0 +1,65 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2026 SUSE S.A.  All Rights Reserved.
> +#
> +# FS QA Test 357
> +#
> +# Make sure on degraded RAID5/6, RMW writes won't return false errors
> +# when some blocks do not have checksums.
> +#
> +. ./common/preamble
> +
> +_begin_fstest auto raid volume
> +
> +_fixed_by_kernel_commit xxxxxxxxxxxx \
> +	"btrfs: raid56: do not verify the content if there is no data checksum"
> +
> +_require_command "$WIPEFS_PROG" wipefs
> +_require_scratch_dev_pool 4
> +_scratch_dev_pool_get 4
> +
> +fio_job_file=$tmp.fio
> +cat > $fio_job_file << EOF
> +[sync_randwrite]
> +directory=$SCRATCH_MNT
> +rw=randwrite
> +filesize=512M
> +bs=4K
> +fdatasync=8
> +time_based
> +fallocate=posix
> +runtime=15
> +EOF
> +
> +_require_fio "$fio_job_file"
> +
> +# The target to remove for degraded mount.
> +dev2="${SCRATCH_DEV_NAME[1]}"
> +
> +workload()
> +{
> +	local profile=$1
> +	_scratch_pool_mkfs "-m raid1 -d $profile" >> $seqres.full 2>&1
> +	$WIPEFS_PROG -fa "$dev2" >> $seqres.full 2>&1
> +	_scratch_mount -o degraded
> +
> +	# The fio job will do fsync after 8 4K writes, which is not enough to
> +	# fill a full stripe and always trigger RMW.
> +	# And the target file is preallocated, after some writes a full stripe
> +	# can have blocks with csum and some blocks without csum.
> +	#
> +	# Unpatched kernels will try to verify the checksum even if there is no
> +	# csum and fail the RMW, causing fio to fail.
> +	$FIO_PROG $fio_job_file >> $seqres.full 2>&1
> +	if [ $? -ne 0 ]; then
> +		echo "fio failed on degraded $profile"
> +	fi
> +	_scratch_unmount
> +}
> +
> +workload raid5
> +workload raid6
> +
> +_scratch_dev_pool_put
> +echo "Silence is golden"
> +_exit 0
> diff --git a/tests/btrfs/357.out b/tests/btrfs/357.out
> new file mode 100644
> index 00000000..25875c6d
> --- /dev/null
> +++ b/tests/btrfs/357.out
> @@ -0,0 +1,2 @@
> +QA output created by 357
> +Silence is golden
> -- 
> 2.51.2
> 
>