xfs: Test infinite loop while searching for a free inode slot

Tests the search algorithm for a free inode slot in a specific AG,
done in xfs_dialloc_ag_inobt().

When finobt is not used, and agi->freecount is not 0, XFS will scan
the AG inode tree looking for a free inode slot, but if
agi->freecount is corrupted, and there is no free slot at all, it
will end up in an infinite loop.

This test checks for the infinite loop fix.

Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

tests/xfs/115

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+#! /bin/bash
+# FS QA Test 115
+#
+# Check if the filesystem will lockup when trying to allocate a new inode in
+# an AG with no free inodes but with a corrupted agi->freecount showing free inodes.
+#
+# At the end of the test, the scratch device will purposely be in a corrupted
+# state, so there is no need for checking that.
+#-----------------------------------------------------------------------
+# Copyright (c) 2017 Red Hat, Inc.  All Rights Reserved.
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+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.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs generic
+_supported_os Linux
+_require_scratch_nocheck
+# we corrupt XFS on purpose, and debug built XFS would crash due to assert
+# failure, so skip if we're testing on a debug built XFS
+_require_no_xfs_debug
+_disable_dmesg_check
+
+# Make sure we disable finobt if the filesystem supports it, otherwise, just
+# initialize it with default options.
+_scratch_mkfs | grep -q "finobt=1" && _scratch_mkfs -m "finobt=0" >/dev/null 2>&1
+
+# Get the amount of free inodes from the AGI 0, so we can fill up the freecount
+# structure.
+freecount=`_scratch_xfs_db -c "agi 0" -c "p freecount" | cut -d' ' -f 3`
+
+_scratch_mount
+
+# At the end of filesystem's initialization, AG 0 will have $freecount free
+# inodes in the agi->freecount, create $freecount extra dummy files to fill it.
+for i in `seq 1 $freecount`; do
+	touch $SCRATCH_MNT/dummy_file$i
+done
+
+_scratch_unmount
+
+# agi->freecount is 0 here, corrupt it to show extra free inodes
+_scratch_xfs_db -x -c "agi 0" -c "write freecount 10" >> $seqres.full 2>&1
+
+_scratch_mount
+
+# Lock up a buggy kernel
+touch $SCRATCH_MNT/lockupfile >> $seqres.full 2>&1
+
+# If we reach this point, the filesystem is fixed
+echo "Silence is golden"
+status=0
+exit

tests/xfs/115.out

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+QA output created by 115
+Silence is golden