[PATCH] ext4: fix check to prevent initializing reserved inodes

[Theodore Ts'o]

Commit 5012284700775a4e6e3fbe7eac4c543c4874b559 upstream.

Commit 8844618d8aa7: "ext4: only look at the bg_flags field if it is
valid" will complain if block group zero does not have the
EXT4_BG_INODE_ZEROED flag set.  Unfortunately, this is not correct,
since a freshly created file system has this flag cleared.  It gets
almost immediately after the file system is mounted read-write --- but
the following somewhat unlikely sequence will end up triggering a
false positive report of a corrupted file system:

   mkfs.ext4 /dev/vdc
   mount -o ro /dev/vdc /vdc
   mount -o remount,rw /dev/vdc

Instead, when initializing the inode table for block group zero, test
to make sure that itable_unused count is not too large, since that is
the case that will result in some or all of the reserved inodes
getting cleared.

This fixes the failures reported by Eric Whiteney when running
generic/230 and generic/231 in the the nojournal test case.

Fixes: 8844618d8aa7 ("ext4: only look at the bg_flags field if it is valid")
Reported-by: Eric Whitney <enwlinux@xxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
---
 fs/ext4/ialloc.c | 5 ++++-
 fs/ext4/super.c  | 8 +-------
 2 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index ffaf66a51de3..4f78e099de1d 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -1316,7 +1316,10 @@ int ext4_init_inode_table(struct super_block *sb, ext4_group_t group,
 			    ext4_itable_unused_count(sb, gdp)),
 			    sbi->s_inodes_per_block);
 
-	if ((used_blks < 0) || (used_blks > sbi->s_itb_per_group)) {
+	if ((used_blks < 0) || (used_blks > sbi->s_itb_per_group) ||
+	    ((group == 0) && ((EXT4_INODES_PER_GROUP(sb) -
+			       ext4_itable_unused_count(sb, gdp)) <
+			      EXT4_FIRST_INO(sb)))) {
 		ext4_error(sb, "Something is wrong with group %u: "
 			   "used itable blocks: %d; "
 			   "itable unused count: %u",
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 41ef83471ea5..04f49572a9a0 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3031,14 +3031,8 @@ static ext4_group_t ext4_has_uninit_itable(struct super_block *sb)
 		if (!gdp)
 			continue;
 
-		if (gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_ZEROED))
-			continue;
-		if (group != 0)
+		if (!(gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_ZEROED)))
 			break;
-		ext4_error(sb, "Inode table for bg 0 marked as "
-			   "needing zeroing");
-		if (sb->s_flags & MS_RDONLY)
-			return ngroups;
 	}
 
 	return group;
-- 
2.18.0.rc0