GIT: unionfs2-2.6.27.y: ext4: check s_log_groups_per_flex in online resize code

[Erez Zadok]

commit 805fe57fb54f9f66256a2c0f81b11abeb83b0142
Author: Eric Sandeen <sandeen at redhat.com>
Date:   Sun May 16 01:00:00 2010 -0400

    ext4: check s_log_groups_per_flex in online resize code
    
    commit 42007efd569f1cf3bfb9a61da60ef6c2179508ca upstream.
    
    If groups_per_flex < 2, sbi->s_flex_groups[] doesn't get filled out,
    and every other access to this first tests s_log_groups_per_flex;
    same thing needs to happen in resize or we'll wander off into
    a null pointer when doing an online resize of the file system.
    
    Thanks to Christoph Biedl, who came up with the trivial testcase:
    
    # truncate --size 128M fsfile
    # mkfs.ext3 -F fsfile
    # tune2fs -O extents,uninit_bg,dir_index,flex_bg,huge_file,dir_nlink,extra_isize fsfile
    # e2fsck -yDf -C0 fsfile
    # truncate --size 132M fsfile
    # losetup /dev/loop0 fsfile
    # mount /dev/loop0 mnt
    # resize2fs -p /dev/loop0
    
    	https://bugzilla.kernel.org/show_bug.cgi?id=13549
    
    Reported-by: Alessandro Polverini <alex at nibbles.it>
    Test-case-by: Christoph Biedl  <bugzilla.kernel.bpeb at manchmal.in-ulm.de>
    Signed-off-by: Eric Sandeen <sandeen at redhat.com>
    Signed-off-by: "Theodore Ts'o" <tytso at mit.edu>
    Signed-off-by: Greg Kroah-Hartman <gregkh at suse.de>

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 0070431..f7f5995 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -935,7 +935,8 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
 	percpu_counter_add(&sbi->s_freeinodes_counter,
 			   EXT4_INODES_PER_GROUP(sb));
 
-	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
+	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
+	    sbi->s_log_groups_per_flex) {
 		ext4_group_t flex_group;
 		flex_group = ext4_flex_group(sbi, input->group);
 		sbi->s_flex_groups[flex_group].free_blocks +=