btrfs: add test for cleaner thread under seed-sprout

We have a longstanding bug that creating a seed sprout fs with the
ro->rw transition done with

mount -o remount,rw $mnt

instead of

umount $mnt
mount $sprout_dev $mnt

results in an fs without BTRFS_FS_OPEN set, which fails to ever run the
critical btrfs cleaner thread.

This test reproduces that bug and detects it by creating and deleting a
subvolume, then triggering the cleaner thread. The expected behavior is
for the cleaner thread to delete the stale subvolume and for the list to
show no entries. Without the fix, we see a DELETED entry for the subvol.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: Zorro Lang <zlang@kernel.org>

diff --git a/tests/btrfs/323 b/tests/btrfs/323
new file mode 100755 (executable)
index 0000000..b7421f6
--- /dev/null
+++ b/tests/btrfs/323
@@ -0,0 +1,47 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2024 Meta Platforms, Inc.  All Rights Reserved.
+#
+# FS QA Test 323
+#
+# Test that remounted seed/sprout device FS is fully functional. For example, that it can purge stale subvolumes.
+#
+. ./common/preamble
+_begin_fstest auto quick seed remount volume
+
+. ./common/filter
+_require_command "$BTRFS_TUNE_PROG" btrfstune
+_require_scratch_dev_pool 2
+
+_fixed_by_kernel_commit XXXXXXXX \
+       "btrfs: do not clear read-only when adding sprout device"
+
+_scratch_dev_pool_get 1
+_spare_dev_get
+
+# create a read-only fs based off a read-only seed device
+_scratch_mkfs >>$seqres.full
+$BTRFS_TUNE_PROG -S 1 $SCRATCH_DEV
+_scratch_mount 2>&1 | _filter_scratch
+_btrfs device add -f $SPARE_DEV $SCRATCH_MNT >>$seqres.full
+
+# switch ro to rw, checking that it was ro before and rw after
+findmnt -n -O ro -o TARGET $SCRATCH_MNT | _filter_scratch
+_mount -o remount,rw $SCRATCH_MNT
+findmnt -n -O rw -o TARGET $SCRATCH_MNT | _filter_scratch
+
+# do stuff in the seed/sprout fs
+_btrfs subvolume create $SCRATCH_MNT/subv
+_btrfs subvolume delete $SCRATCH_MNT/subv
+
+# trigger cleaner thread without remounting
+_btrfs filesystem sync $SCRATCH_MNT
+
+# expect no deleted subvolumes remaining
+$BTRFS_UTIL_PROG subvolume list -d $SCRATCH_MNT
+
+_spare_dev_put
+
+# success, all done
+status=0
+exit

diff --git a/tests/btrfs/323.out b/tests/btrfs/323.out
new file mode 100644 (file)
index 0000000..1ca2e4b
--- /dev/null
+++ b/tests/btrfs/323.out
@@ -0,0 +1,4 @@
+QA output created by 323
+mount: SCRATCH_MNT: WARNING: source write-protected, mounted read-only.
+SCRATCH_MNT
+SCRATCH_MNT