truncate-resize-size-to-avoid-too-small-last-bg

   1 ext4: fix online resize's handling of a too-small final block group
   2
   3 Avoid growing the file system to an extent so that the last block
   4 group is too small to hold all of the metadata that must be stored in
   5 the block group.
   6
   7 This problem can be triggered with the following reproducer:
   8
   9 umount /mnt
  10 mke2fs -F -m0 -b 4096 -t ext4 -O resize_inode,^has_journal \
  11         -E resize=1073741824 /tmp/foo.img 128M
  12 mount /tmp/foo.img /mnt
  13 truncate --size 1708M /tmp/foo.img
  14 resize2fs /dev/loop0 295400
  15 umount /mnt
  16 e2fsck -fy /tmp/foo.img
  17
  18 Reported-by: Torsten Hilbrich <torsten.hilbrich@secunet.com>
  19 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  20 Cc: stable@vger.kernel.org
  21 ---
  22  fs/ext4/resize.c | 20 ++++++++++++++++++++
  23  1 file changed, 20 insertions(+)
  24
  25 diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
  26 index e5fb38451a73..33655a6eff4d 100644
  27 --- a/fs/ext4/resize.c
  28 +++ b/fs/ext4/resize.c
  29 @@ -1986,6 +1986,26 @@ int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
  30                 }
  31         }
  32
  33 +       /*
  34 +        * Make sure the last group has enough space so that it's
  35 +        * guaranteed to have enough space for all metadata blocks
  36 +        * that it might need to hold.  (We might not need to store
  37 +        * the inode table blocks in the last block group, but there
  38 +        * will be cases where this might be needed.)
  39 +        */
  40 +       if ((ext4_group_first_block_no(sb, n_group) +
  41 +            ext4_group_overhead_blocks(sb, n_group) + 2 +
  42 +            sbi->s_itb_per_group + sbi->s_cluster_ratio) >= n_blocks_count) {
  43 +               n_blocks_count = ext4_group_first_block_no(sb, n_group);
  44 +               n_group--;
  45 +               n_blocks_count_retry = 0;
  46 +               if (resize_inode) {
  47 +                       iput(resize_inode);
  48 +                       resize_inode = NULL;
  49 +               }
  50 +               goto retry;
  51 +       }
  52 +
  53         /* extend the last group */
  54         if (n_group == o_group)
  55                 add = n_blocks_count - o_blocks_count;