Re: [PATCH] btrfs/255: add test for quota disable in parallel with balance

[Filipe Manana <fdmanana@kernel.org>]

On Mon, Jan 17, 2022 at 09:57:05AM +0900, Shin'ichiro Kawasaki wrote:
> Test quota disable during btrfs balance and confirm it does not cause
> kernel hang. This is a regression test for the problem reported to
> linux-btrfs list [1]. The hang was recreated using the test case and
> memory backed null_blk device with 5GB size as the scratch device.
> 
> [1] https://lore.kernel.org/linux-btrfs/20220115053012.941761-1-shinichiro.kawasaki@wdc.com/
> 
> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> ---
>  tests/btrfs/255     | 42 ++++++++++++++++++++++++++++++++++++++++++
>  tests/btrfs/255.out |  2 ++
>  2 files changed, 44 insertions(+)
>  create mode 100755 tests/btrfs/255
>  create mode 100644 tests/btrfs/255.out
> 
> diff --git a/tests/btrfs/255 b/tests/btrfs/255
> new file mode 100755
> index 00000000..16b682ca
> --- /dev/null
> +++ b/tests/btrfs/255
> @@ -0,0 +1,42 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2022 Western Digital Corporation or its affiliates.
> +#
> +# FS QA Test No. btrfs/255
> +#
> +# Confirm that disabling quota during balance does not hang
> +#
> +. ./common/preamble
> +_begin_fstest auto qgroup

Should have "balance" as well.

> +
> +# real QA test starts here
> +_supported_fs btrfs
> +_require_scratch
> +
> +_scratch_mkfs >> $seqres.full 2>&1
> +_scratch_mount
> +
> +# Fill 40% of the device or 2GB
> +fill_percent=40
> +max_fillsize=$((2*1024*1024*1024))

If the test requires some minimum size, than it should call

   _require_scratch_size <size in KB>

Also please make it a bit more readable by adding a single space before
and after each *, i.e. 2 * 1024 * 1024 ... instead of 2*1024*1024.

> +
> +devsize=$(($(_get_device_size $SCRATCH_DEV) * 512))
> +fillsize=$((devsize * fill_percent / 100))
> +((fillsize > max_fillsize)) && fillsize=$max_fillsize
> +
> +fs=$((4096*1024))

Same here.

> +for ((i=0; i * fs < fillsize; i++)); do

And here (i = 0 vs i=0).

> +	dd if=/dev/zero of=$SCRATCH_MNT/file.$i bs=$fs count=1 \
> +	   >> $seqres.full 2>&1
> +done
> +echo 3 > /proc/sys/vm/drop_caches

Why the drop_caches? Please add a comment explaining why it is needed.

> +
> +# Run btrfs balance and quota enable/disable in parallel
> +_run_btrfs_balance_start $SCRATCH_MNT >> $seqres.full &
> +$BTRFS_UTIL_PROG quota enable $SCRATCH_MNT
> +$BTRFS_UTIL_PROG quota disable $SCRATCH_MNT

This seems very timing sensitive.
It would be a better stress test if we do the enable/disable in a loop,
say 10 or 20 iterations, while another process keeps running balance in
parallel and then is killed after the main process finishes the loop of
enable/disable quotas.

Thanks.

> +wait
> +
> +echo "Silence is golden"
> +status=0
> +exit
> diff --git a/tests/btrfs/255.out b/tests/btrfs/255.out
> new file mode 100644
> index 00000000..7eefb828
> --- /dev/null
> +++ b/tests/btrfs/255.out
> @@ -0,0 +1,2 @@
> +QA output created by 255
> +Silence is golden
> -- 
> 2.33.1
>