generic: test dm-thin running out of data space vs concurrent discard

If a user constructs a test that loops repeatedly over below steps
on dm-thin, block allocation can fail due to discards not having
completed yet (Fixed by a685557 dm thin: handle running out of data
space vs concurrent discard):

1) fill thin device via filesystem file
2) remove file
3) fstrim

And this maybe cause a deadlock (fast device likes ramdisk can help
a lot) when racing a fstrim with a filesystem (XFS) shutdown. (Fixed
by 8c81dd46ef3c Force log to disk before reading the AGF during a
fstrim)

This case can reproduce both two bugs if they're not fixed. If only
the dm-thin bug is fixed, then the test will pass. If only the fs
bug is fixed, then the test will fail. If both of bugs aren't fixed,
the test will hang.

Signed-off-by: Zorro Lang <zlang@redhat.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/500

@@ -0,0 +1,92 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2018 Red Hat Inc.  All Rights Reserved.
+#
+# FS QA Test No. 500
+#
+# Race test running out of data space with concurrent discard operation on
+# dm-thin.
+#
+# If a user constructs a test that loops repeatedly over below steps on
+# dm-thin, block allocation can fail due to discards not having completed
+# yet (Fixed by a685557 dm thin: handle running out of data space vs
+# concurrent discard):
+# 1) fill thin device via filesystem file
+# 2) remove file
+# 3) fstrim
+#
+# And this maybe cause a deadlock when racing a fstrim with a filesystem
+# (XFS) shutdown. (Fixed by 8c81dd46ef3c Force log to disk before reading
+# the AGF during a fstrim)
+#
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+	_dmthin_cleanup
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+. ./common/dmthin
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+_supported_fs generic
+_supported_os Linux
+_require_scratch_nocheck
+_require_dm_target thin-pool
+
+# Require underlying device support discard
+_scratch_mkfs >>$seqres.full 2>&1
+_scratch_mount
+_require_batched_discard $SCRATCH_MNT
+_scratch_unmount
+
+# Create a thin pool and a *slightly smaller* thin volume, it's helpful
+# to reproduce the bug
+BACKING_SIZE=$((128 * 1024 * 1024 / 512))	# 128M
+VIRTUAL_SIZE=$((BACKING_SIZE + 1024))		# 128M + 1k
+CLUSTER_SIZE=$((64 * 1024 / 512))		# 64K
+
+_dmthin_init $BACKING_SIZE $VIRTUAL_SIZE $CLUSTER_SIZE 0
+_dmthin_set_fail
+_mkfs_dev $DMTHIN_VOL_DEV
+_dmthin_mount
+
+# There're two bugs at here, one is dm-thin bug, the other is filesystem
+# (XFS especially) bug. The dm-thin bug can't handle running out of data
+# space with concurrent discard well. Then the dm-thin bug cause fs unmount
+# hang when racing a fstrim with a filesystem shutdown.
+#
+# If both of two bugs haven't been fixed, below test maybe cause deadlock.
+# Else if the fs bug has been fixed, but the dm-thin bug hasn't. below test
+# will cause the test fail (no deadlock).
+# Else the test will pass.
+for ((i=0; i<20; i++)); do
+	$XFS_IO_PROG -f -c "pwrite -b 64k 0 256M" \
+		$SCRATCH_MNT/testfile &>/dev/null
+	rm -f $SCRATCH_MNT/testfile
+	$FSTRIM_PROG $SCRATCH_MNT
+done
+
+_dmthin_check_fs
+_dmthin_cleanup
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit

tests/generic/500.out

@@ -0,0 +1,2 @@
+QA output created by 500
+Silence is golden

tests/generic/group

@@ -502,3 +502,4 @@
 497 auto quick swap collapse
 498 auto quick log
 499 auto quick rw collapse zero
+500 auto thin trim