ext4: prevent initializing reserved inodes

Check the block group zero and prevent initializing reserved inodes.
But in some special cases, the reserved inode may not all belong to
the group zero, it may exist into the second group if we format 
filesystem below.

  mkfs.ext4 -b 4096 -g 8192 -N 1024 -I 4096 /dev/sda

So, it will end up triggering a false positive report of a corrupted
file system

It's a regression test for kernel commit a149d2a5cabb ("ext4: fix
check to prevent false positive report of incorrect used inodes")

Signed-off-by: Chen Long <chenlongcl.chen@huawei.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/ext4/049

@@ -0,0 +1,67 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021 Huawei.  All Rights Reserved.
+#
+# FS QA Test 049
+#
+# Regression test for kernel commit a149d2a5cabb (ext4: fix check to prevent
+# false positive report of incorrect used inodes)
+#
+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 $seqres.full
+
+# real QA test starts here
+_supported_fs ext4
+_require_scratch
+
+sdev=$(_short_dev ${SCRATCH_DEV})
+# default sleep interval
+sleep_time=5
+
+echo "+ create scratch fs"
+_scratch_mkfs_ext4 -b 4096 -g 8192 -N 1024 -I 4096 >> $seqres.full 2>&1
+
+echo "+ mount fs"
+_scratch_mount -o errors=remount-ro
+# The default maximum wake-up delay of the lazy init thread of ext4 is
+# EXT4_DEF_LI_MAX_START_DELAY (5s).
+# After mounting the file system, the lazy init thread will be awakened to
+# perform group initialization at 0~5s after the current time. If an error
+# is detected during the initialization process, it will be set to read-only,
+# so the test case needs to delay a little while waiting for the init thread
+# to execute.
+sleep $sleep_time
+
+echo "+ check mountpoint status"
+cat /proc/self/mounts | grep -w ${SCRATCH_MNT} | \
+    $AWK_PROG '{print $4}' | grep -oE '^rw,' | tee -a $seqres.full
+
+echo "+ check mountpoint writability"
+test -w $SCRATCH_MNT || echo "scratch mount should still be writable"
+
+echo "+ check dmesg"
+_check_dmesg_for "\(${sdev}\): Remounting filesystem read-only" && \
+    echo "scratch dev should not be remounted to read-only"
+
+# success, all done
+status=0
+exit

tests/ext4/049.out

@@ -0,0 +1,7 @@
+QA output created by 049
++ create scratch fs
++ mount fs
++ check mountpoint status
+rw,
++ check mountpoint writability
++ check dmesg

tests/ext4/group

@@ -51,6 +51,7 @@
 046 auto prealloc quick
 047 auto quick dax
 048 auto quick dir
+049 auto quick
 271 auto rw quick
 301 aio auto ioctl rw stress defrag
 302 aio auto ioctl rw stress defrag