[PATCH] generic: add swapfile maxpages regression test

["Darrick J. Wong" <djwong@kernel.org>]

From: Darrick J. Wong <djwong@kernel.org>

Add regression test for "mm/swap: consider max pages in
iomap_swapfile_add_extent".

Cc: Gang Deng <gavin.dg@linux.alibaba.com>
Cc: Xu Yu <xuyu@linux.alibaba.com>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
 tests/generic/727     |   62 +++++++++++++++++++++++++++++++++++++++++++++++++
 tests/generic/727.out |    2 ++
 2 files changed, 64 insertions(+)
 create mode 100755 tests/generic/727
 create mode 100644 tests/generic/727.out

diff --git a/tests/generic/727 b/tests/generic/727
new file mode 100755
index 00000000..a546ad51
--- /dev/null
+++ b/tests/generic/727
@@ -0,0 +1,62 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021 Oracle.  All Rights Reserved.
+#
+# FS QA Test 727
+#
+# Regression test for "mm/swap: consider max pages in iomap_swapfile_add_extent"
+
+# Xu Yu found that the iomap swapfile activation code failed to constrain
+# itself to activating however many swap pages that the mm asked us for.  This
+# is an deviation in behavior from the classic swapfile code.  It also leads to
+# kernel memory corruption if the swapfile is cleverly constructed.
+#
+. ./common/preamble
+_begin_fstest auto swap
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+	test -n "$swapfile" && swapoff $swapfile &> /dev/null
+}
+
+# real QA test starts here
+_supported_fs generic
+_require_scratch_swapfile
+
+_scratch_mkfs >> $seqres.full
+_scratch_mount >> $seqres.full
+
+# Assuming we're not borrowing a FAT16 partition from Windows 3.1, we need an
+# unlikely enough name that we can grep /proc/swaps for this.
+swapfile=$SCRATCH_MNT/386spart.par
+_format_swapfile $swapfile 1m >> $seqres.full
+
+swapfile_pages() {
+	local swapfile="$1"
+
+	grep "$swapfile" /proc/swaps | awk '{print $3}'
+}
+
+_swapon_file $swapfile
+before_pages=$(swapfile_pages "$swapfile")
+swapoff $swapfile
+
+# Extend the length of the swapfile but do not rewrite the header.
+# The subsequent swapon should set up 1MB worth of pages, not 2MB.
+$XFS_IO_PROG -f -c 'pwrite 1m 1m' $swapfile >> $seqres.full
+
+_swapon_file $swapfile
+after_pages=$(swapfile_pages "$swapfile")
+swapoff $swapfile
+
+# Both swapon attempts should have found the same number of pages.
+test "$before_pages" -eq "$after_pages" || \
+	echo "swapon added $after_pages pages, expected $before_pages"
+
+# success, all done
+echo Silence is golden
+status=0
+exit
diff --git a/tests/generic/727.out b/tests/generic/727.out
new file mode 100644
index 00000000..2de2b4b2
--- /dev/null
+++ b/tests/generic/727.out
@@ -0,0 +1,2 @@
+QA output created by 727
+Silence is golden