[PATCH v2 3/5] fstests: add fsstress + compaction test

[Luis Chamberlain <mcgrof@kernel.org>]

Running compaction while we run fsstress can crash older kernels as per
korg#218227 [0], the fix for that [0] has been posted [1] that patch
was merged on v6.9-rc6 fixed by commit d99e3140a4d3 ("mm: turn
folio_test_hugetlb into a PageType"). This test reproduces that crash
right away.

But we have more work to do ...

Even on v6.10-rc2 where this kernel commit is already merged we can
still deadlock when running fsstress and at the same time triggering
compaction, this is a new issue being reported now through this patch,
but this patch also serves as a reproducer with a high confidence. At
least for XFS running this test ~ 44 times will deadlock.

If you enable CONFIG_PROVE_LOCKING with the defaults you will end up
with a complaint about increasing MAX_LOCKDEP_CHAIN_HLOCKS [1], if
you adjust that you then end up with a few soft lockup complaints and
some possible deadlock candidates to evaluate [2].

Provide a simple reproducer and pave the way so we keep on testing this.

[0] https://bugzilla.kernel.org/show_bug.cgi?id=218227
[1] https://gist.github.com/mcgrof/824913b645892214effeb1631df75072
[2] https://gist.github.com/mcgrof/926e183d21c5c4c55d74ec90197bd77a

Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
 common/rc             |  7 +++++
 tests/generic/750     | 63 +++++++++++++++++++++++++++++++++++++++++++
 tests/generic/750.out |  2 ++
 3 files changed, 72 insertions(+)
 create mode 100755 tests/generic/750
 create mode 100644 tests/generic/750.out

diff --git a/common/rc b/common/rc
index e812a2f7cc67..18ad25662d5c 100644
--- a/common/rc
+++ b/common/rc
@@ -151,6 +151,13 @@ _require_hugepages()
 		_notrun "Kernel does not report huge page size"
 }
 
+# Requires CONFIG_COMPACTION
+_require_vm_compaction()
+{
+	if [ ! -f /proc/sys/vm/compact_memory ]; then
+	    _notrun "Need compaction enabled CONFIG_COMPACTION=y"
+	fi
+}
 # Get hugepagesize in bytes
 _get_hugepagesize()
 {
diff --git a/tests/generic/750 b/tests/generic/750
new file mode 100755
index 000000000000..3057937d7176
--- /dev/null
+++ b/tests/generic/750
@@ -0,0 +1,63 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2024 Luis Chamberlain.  All Rights Reserved.
+#
+# FS QA Test 750
+#
+# fsstress + memory compaction test
+#
+. ./common/preamble
+_begin_fstest auto rw long_rw stress soak smoketest
+
+_cleanup()
+{
+	cd /
+	rm -f $runfile
+	rm -f $tmp.*
+	kill -9 $trigger_compaction_pid > /dev/null 2>&1
+	$KILLALL_PROG -9 fsstress > /dev/null 2>&1
+
+	wait > /dev/null 2>&1
+}
+
+# Import common functions.
+
+# real QA test starts here
+
+_supported_fs generic
+
+_require_scratch
+_require_vm_compaction
+_require_command "$KILLALL_PROG" "killall"
+
+# We still deadlock with this test on v6.10-rc2, we need more work.
+# but the below makes things better.
+_fixed_by_git_commit kernel d99e3140a4d3 \
+	"mm: turn folio_test_hugetlb into a PageType"
+
+echo "Silence is golden"
+
+_scratch_mkfs > $seqres.full 2>&1
+_scratch_mount >> $seqres.full 2>&1
+
+nr_cpus=$((LOAD_FACTOR * 4))
+nr_ops=$((25000 * nr_cpus * TIME_FACTOR))
+fsstress_args=(-w -d $SCRATCH_MNT -n $nr_ops -p $nr_cpus)
+test -n "$SOAK_DURATION" && fsstress_args+=(--duration="$SOAK_DURATION")
+
+# start a background trigger for memory compaction
+runfile="$tmp.compaction"
+touch $runfile
+while [ -e $runfile ]; do
+	echo 1 > /proc/sys/vm/compact_memory
+	sleep 5
+done &
+trigger_compaction_pid=$!
+
+$FSSTRESS_PROG $FSSTRESS_AVOID "${fsstress_args[@]}" >> $seqres.full
+
+rm -f $runfile
+wait > /dev/null 2>&1
+
+status=0
+exit
diff --git a/tests/generic/750.out b/tests/generic/750.out
new file mode 100644
index 000000000000..bd79507b632e
--- /dev/null
+++ b/tests/generic/750.out
@@ -0,0 +1,2 @@
+QA output created by 750
+Silence is golden
-- 
2.43.0