fix-delalloc-release-block-reservation-for-truncate

   1 ext4: Fix delalloc release block reservation for truncate
   2
   3 From: Mingming Cao <cmm@us.ibm.com>
   4
   5 Ext4 will release the reserved blocks for delayed allocations when
   6 inode is truncated/unlinked.  If there is no reserved block at all, we
   7 shouldn't need to do so.  But current code still tries to release the
   8 reserved blocks regardless whether the counters's value is 0.
   9 Continue to do that causes the later calculation to go wrong and a
  10 kernel BUG_ON() caught that. This doesn't happen for extent-based
  11 files, as the calculation for 0 reserved blocks was right for extent
  12 based file.
  13
  14 This patch fixed the kernel BUG() due to above reason.  It adds checks
  15 for 0 to avoid unnecessary release and fix calculation for non-extent
  16 files.
  17
  18 Signed-off-by: Mingming Cao <cmm@us.ibm.com>
  19 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  20 ---
  21 ---
  22  fs/ext4/inode.c |   21 +++++++++++++++++++++
  23  1 file changed, 21 insertions(+)
  24
  25 Index: linux-2.6.27-rc3/fs/ext4/inode.c
  26 ===================================================================
  27 --- linux-2.6.27-rc3.orig/fs/ext4/inode.c       2008-08-19 15:56:49.000000000 -0700
  28 +++ linux-2.6.27-rc3/fs/ext4/inode.c    2008-08-19 15:57:12.000000000 -0700
  29 @@ -1005,6 +1005,9 @@ static int ext4_indirect_calc_metadata_a
  30   */
  31  static int ext4_calc_metadata_amount(struct inode *inode, int blocks)
  32  {
  33 +       if (!blocks)
  34 +               return 0;
  35 +
  36         if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL)
  37                 return ext4_ext_calc_metadata_amount(inode, blocks);
  38
  39 @@ -1559,7 +1562,25 @@ static void ext4_da_release_space(struct
  40         struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
  41         int total, mdb, mdb_free, release;
  42
  43 +       if (!to_free)
  44 +               return;         /* Nothing to release, exit */
  45 +
  46         spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
  47 +
  48 +       if (!EXT4_I(inode)->i_reserved_data_blocks) {
  49 +               /*
  50 +                * if there is no reserved blocks, but we try to free some
  51 +                * then the counter is messed up somewhere.
  52 +                * but since this function is called from invalidate
  53 +                * page, it's harmless to return without any action
  54 +                */
  55 +               printk(KERN_INFO "ext4 delalloc try to release %d reserved "
  56 +                           "blocks for inode %lu, but there is no reserved "
  57 +                           "data blocks\n", to_free, inode->i_ino);
  58 +               spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
  59 +               return;
  60 +       }
  61 +
  62         /* recalculate the number of metablocks still need to be reserved */
  63         total = EXT4_I(inode)->i_reserved_data_blocks - to_free;
  64         mdb = ext4_calc_metadata_amount(inode, total);