[PATCH] generic: test COW writeback failure when overlapping non-shared blocks

[Brian Foster <bfoster@redhat.com>]

Test that COW writeback that overlaps non-shared delalloc blocks
does not leave around stale delalloc blocks on I/O failure. This
triggers assert failures and free space accounting corruption on
XFS.

Signed-off-by: Brian Foster <bfoster@redhat.com>
---

This test targets the problem addressed by the following patch in XFS:

https://lore.kernel.org/linux-xfs/20211021163330.1886516-1-bfoster@redhat.com/

Brian

 tests/generic/651     | 53 +++++++++++++++++++++++++++++++++++++++++++
 tests/generic/651.out |  2 ++
 2 files changed, 55 insertions(+)
 create mode 100755 tests/generic/651
 create mode 100644 tests/generic/651.out

diff --git a/tests/generic/651 b/tests/generic/651
new file mode 100755
index 00000000..8d4e6728
--- /dev/null
+++ b/tests/generic/651
@@ -0,0 +1,53 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021 Red Hat, Inc.  All Rights Reserved.
+#
+# FS QA Test 651
+#
+# Test that COW writeback that overlaps non-shared delalloc blocks does not
+# leave around stale delalloc blocks on I/O failure. This triggers assert
+# failures and free space accounting corruption on XFS.
+#
+. ./common/preamble
+_begin_fstest auto quick clone
+
+_cleanup()
+{
+	_cleanup_flakey
+	cd /
+	rm -r -f $tmp.*
+}
+
+# Import common functions.
+. ./common/reflink
+. ./common/dmflakey
+
+# real QA test starts here
+_supported_fs generic
+_require_scratch_reflink
+_require_flakey_with_error_writes
+
+_scratch_mkfs >> $seqres.full
+_init_flakey
+_mount_flakey
+
+# create two files that share a single block
+$XFS_IO_PROG -fc "pwrite 4k 4k" $SCRATCH_MNT/file1 >> $seqres.full
+cp --reflink $SCRATCH_MNT/file1 $SCRATCH_MNT/file2
+
+# Perform a buffered write across the shared and non-shared blocks. On XFS, this
+# creates a COW fork extent that covers the shared block as well as the just
+# created non-shared delalloc block. Fail the writeback to verify that all
+# delayed allocation is cleaned up properly.
+_load_flakey_table $FLAKEY_ERROR_WRITES
+$XFS_IO_PROG -c "pwrite 0 8k" -c fsync $SCRATCH_MNT/file2 >> $seqres.full
+_load_flakey_table $FLAKEY_ALLOW_WRITES
+
+# Try a post-fail reflink and then unmount. Both of these are known to produce
+# errors and/or assert failures on XFS if we trip over a stale delalloc block.
+cp --reflink $SCRATCH_MNT/file2 $SCRATCH_MNT/file3
+_unmount_flakey
+
+# success, all done
+status=0
+exit
diff --git a/tests/generic/651.out b/tests/generic/651.out
new file mode 100644
index 00000000..bd44c80c
--- /dev/null
+++ b/tests/generic/651.out
@@ -0,0 +1,2 @@
+QA output created by 651
+fsync: Input/output error
-- 
2.31.1