Re: [PATCH] generic: add a test that stresses metadata eviction

On Mon, May 18, 2026 at 08:24:53AM +0200, Christoph Hellwig wrote:
> The fsverity test generic/759 could be used to reproduce a regression in
> the xfs buffer hashing.  Carlos Maiolino figured out that even removing
> the fsverity-specific bits would reproduce the issue.  This test is
> thus a copy of generic/759 with the fsverity bits striped out, and
> run 5 times as that seems to be the threshold at which the issue
> reproduces reliably.
> 
> Signed-off-by: Christoph Hellwig <[email protected]>
> ---
> 
> Not sure how to best credit Eric for the original patch and Carlos
> for the extraction, any ideas?

To be fair, Andrey initially suggested stripping off the fs-verity
parts, IIRC because he wanted to isolate his own series from this crash.
My role was mostly reproduce it and hunt the bug down.
Risking to come with yet another tag, perhaps something like:

Based-on-generic-579-by: <Eric...>

It doesn't look ugly to me, but who knows...

> 
>  tests/generic/4201     | 108 +++++++++++++++++++++++++++++++++++++++++
>  tests/generic/4201.out |   2 +
>  2 files changed, 110 insertions(+)
>  create mode 100755 tests/generic/4201
>  create mode 100644 tests/generic/4201.out
> 
> diff --git a/tests/generic/4201 b/tests/generic/4201
> new file mode 100755
> index 000000000000..fc367beeadaf
> --- /dev/null
> +++ b/tests/generic/4201
> @@ -0,0 +1,108 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright 2019 Google LLC
> +#
> +# FS QA Test generic/4201
> +#
> +# Race dropping file systems caches vs fsstress an repeated reading of files.
> +# Based on generic/579 with the fsverity bits stripped out, and an increased
> +# number of runs.
> +#
> +. ./common/preamble
> +_begin_fstest auto stress
> +
> +stop_run()
> +{
> +	# Stop all subprocesses.
> +	_kill_fsstress
> +	touch $tmp.done
> +	wait
> +}
> +
> +_cleanup()
> +{
> +	stop_run
> +	rm -f $tmp.*
> +}
> +
> +. ./common/filter
> +
> +fsv_file_size=10000000
> +nproc_enabler=$((4 * LOAD_FACTOR))
> +nproc_reader=$((6 * LOAD_FACTOR))
> +nproc_stress=$((3 * LOAD_FACTOR))
> +runtime=$((20 * TIME_FACTOR))
> +
> +run_test()
> +{
> +	rm -rf $tmp.done
> +
> +	# Create the test files and start the fs-verity enabler processes.
> +	for ((proc = 0; proc < nproc_enabler; proc++)); do
> +		orig_file=$SCRATCH_MNT/orig$proc
> +		fsv_file=$SCRATCH_MNT/fsv$proc
> +		head -c $fsv_file_size /dev/urandom > $orig_file
> +		(
> +			while [ ! -e $tmp.done ]; do
> +				rm -f $fsv_file
> +				cp $orig_file $fsv_file
> +				# Give the readers some time to read from the file.
> +				sleep 0.$((RANDOM % 100))
> +			done
> +		) &
> +	done
> +
> +	# Start the reader processes.
> +	for ((proc = 0; proc < nproc_reader; proc++)); do
> +		(
> +			while [ ! -e $tmp.done ]; do
> +				# Choose a random file for each iteration, so that
> +				# sometimes multiple processes read from the same file.
> +				i=$((RANDOM % nproc_enabler))
> +				orig_file=$SCRATCH_MNT/orig$i
> +				fsv_file=$SCRATCH_MNT/fsv$i
> +
> +				# After the copy from $orig_file to $fsv_file has
> +				# completed, the contents of these two files should
> +				# match, regardless of whether verity has been enabled
> +				# or not yet (or is currently being enabled).
> +				cmp $orig_file $fsv_file |& _filter_scratch | \
> +					sed -e "s/'//g" | \
> +					grep -v "SCRATCH_MNT/fsv$i: No such file or directory" | \
> +					grep -v "EOF on SCRATCH_MNT/fsv$i"
> +				done
> +		) &
> +	done
> +
> +	# Start a process that occasionally runs 'sync && drop_caches'.  This makes more
> +	# reads go through fs-verity for real, rather than just returning pagecache.
> +	(
> +		while [ ! -e $tmp.done ]; do
> +			sleep 2.$((RANDOM % 100))
> +			_scratch_sync && echo 3 > /proc/sys/vm/drop_caches
> +		done
> +	) &
> +
> +	# Start the fsstress processes.
> +	_run_fsstress_bg -p $nproc_stress -l 0 -d $SCRATCH_MNT/stressdir
> +
> +	# Run for a while.
> +	sleep $runtime
> +
> +	stop_run
> +}
> +
> +for i in $(seq 1 5); do
> +	echo "Starting run $i" >> $seqres.full
> +
> +	_scratch_mkfs &>> $seqres.full
> +	_scratch_mount
> +	run_test
> +	_scratch_unmount
> +done
> +
> +echo "Silence is golden"
> +
> +# success, all done
> +status=0
> +exit
> diff --git a/tests/generic/4201.out b/tests/generic/4201.out
> new file mode 100644
> index 000000000000..2c3f3d42ff3f
> --- /dev/null
> +++ b/tests/generic/4201.out
> @@ -0,0 +1,2 @@
> +QA output created by 4201
> +Silence is golden
> -- 
> 2.53.0
> 
>