Re: [PATCH 2/2] xfs: use iomap_valid method to detect stale cached iomaps

[Frank Sorenson <frank@tuxrocks.com>]

On 9/28/22 20:45, Dave Chinner wrote:
> On Tue, Sep 27, 2022 at 09:54:27PM -0700, Darrick J. Wong wrote:

>> Btw, can you share the reproducer?

> Not sure. The current reproducer I have is 2500 lines of complex C
> code that was originally based on a reproducer the original reporter
> provided. It does lots of stuff that isn't directly related to
> reproducing the issue, and will be impossible to review and maintain
> as it stands in fstests.

Too true.  Fortunately, now that I understand the necessary conditions
and IO patterns, I managed to prune it all down to ~75 lines of bash
calling xfs_io.  See below.

Frank
--
Frank Sorenson
sorenson@redhat.com
Principal Software Maintenance Engineer
Global Support Services - filesystems
Red Hat

###########################################
#!/bin/bash
#	Frank Sorenson <sorenson@redhat.com>, 2022

num_files=8
num_writers=3

KiB=1024
MiB=$(( $KiB * $KiB ))
GiB=$(( $KiB * $KiB * $KiB ))

file_size=$(( 500 * $MiB ))
#file_size=$(( 1 * $GiB ))
write_size=$(( 1 * $MiB ))
start_offset=512

num_loops=$(( ($file_size - $start_offset + (($num_writers * $write_size) - 1)) / ($num_writers * $write_size) ))
total_size=$(( ($num_loops * $num_writers * $write_size) + $start_offset ))

cgroup_path=/sys/fs/cgroup/test_write_bug
mkdir -p $cgroup_path || { echo "unable to create cgroup" ; exit ; }

max_mem=$(( 40 * $MiB ))
high_mem=$(( ($max_mem * 9) / 10 ))
echo $high_mem >$cgroup_path/memory.high
echo $max_mem >$cgroup_path/memory.max

mkdir -p testfiles
rm -f testfiles/expected
xfs_io -f -c "pwrite -b $((1 * $MiB)) -S 0x40 0 $total_size" testfiles/expected >/dev/null 2>&1
expected_sum=$(md5sum testfiles/expected | awk '{print $1}')

echo $$ > $cgroup_path/cgroup.procs || exit # put ourselves in the cgroup

do_one_testfile() {
	filenum=$1
	cpids=""
	offset=$start_offset

	rm -f testfiles/test$filenum
	xfs_io -f -c "pwrite -b $start_offset -S 0x40 0 $start_offset" testfiles/test$filenum >/dev/null 2>&1

	while [[ $offset -lt $file_size ]] ; do
		cpids=""
		for i in $(seq 1 $num_writers) ; do
			xfs_io -f -c "pwrite -b $write_size -S 0x40 $(( ($offset + (($num_writers - $i) * $write_size)  ) )) $write_size" testfiles/test$filenum >/dev/null 2>&1 &
			cpids="$cpids $!"
		done
		wait $cpids
		offset=$(( $offset + ($num_writers * $write_size) ))
	done
}

round=1
while [[ 42 ]] ; do
	echo "test round: $round"
	cpids=""
	for i in $(seq 1 $num_files) ; do
		do_one_testfile $i &
		cpids="$cpids $!"
	done
	wait $cpids

	replicated="" # now check the files
	for i in $(seq 1 $num_files) ; do
		sum=$(md5sum testfiles/test$i | awk '{print $1}')
		[[ $sum == $expected_sum ]] || replicated="$replicated testfiles/test$i"
	done

	[[ -n $replicated ]] && break
	round=$(($round + 1))
done
echo "replicated bug with: $replicated"
echo $$ > /sys/fs/cgroup/cgroup.procs
rmdir $cgroup_path