src/patches/suse-2.6.27.31/patches.fixes/ext4-clear-unwritten-flag-after-extent-initialization

   1 From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
   2 Date: Thu, 14 May 2009 21:05:39 +0000 (-0400)
   3 Subject: ext4: Clear the unwritten buffer_head flag after the extent is initialized
   4 Patch-mainline: 2.6.30-rc6
   5 Git-commit: 2a8964d63d50dd2d65d71d342bc7fb6ef4117614
   6 References: bnc#503161
   7
   8 ext4: Clear the unwritten buffer_head flag after the extent is initialized
   9
  10 The BH_Unwritten flag indicates that the buffer is allocated on disk
  11 but has not been written; that is, the disk was part of a persistent
  12 preallocation area.  That flag should only be set when a get_blocks()
  13 function is looking up a inode's logical to physical block mapping.
  14
  15 When ext4_get_blocks_wrap() is called with create=1, the uninitialized
  16 extent is converted into an initialized one, so the BH_Unwritten flag
  17 is no longer appropriate.  Hence, we need to make sure the
  18 BH_Unwritten is not left set, since the combination of BH_Mapped and
  19 BH_Unwritten is not allowed; among other things, it will result ext4's
  20 get_block() to be called over and over again during the write_begin
  21 phase of write(2).
  22
  23 Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
  24 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  25 Acked-by: Jeff Mahoney <jeffm@suse.com>
  26 ---
  27
  28  fs/ext4/inode.c |   13 +++++++++++++
  29  1 file changed, 13 insertions(+)
  30
  31 --- a/fs/ext4/inode.c
  32 +++ b/fs/ext4/inode.c
  33 @@ -1058,6 +1058,7 @@ int ext4_get_blocks_wrap(handle_t *handl
  34         int retval;
  35
  36         clear_buffer_mapped(bh);
  37 +       clear_buffer_unwritten(bh);
  38
  39         /*
  40          * Try to see if we can get  the block without requesting
  41 @@ -1088,6 +1089,18 @@ int ext4_get_blocks_wrap(handle_t *handl
  42                 return retval;
  43
  44         /*
  45 +        * When we call get_blocks without the create flag, the
  46 +        * BH_Unwritten flag could have gotten set if the blocks
  47 +        * requested were part of a uninitialized extent.  We need to
  48 +        * clear this flag now that we are committed to convert all or
  49 +        * part of the uninitialized extent to be an initialized
  50 +        * extent.  This is because we need to avoid the combination
  51 +        * of BH_Unwritten and BH_Mapped flags being simultaneously
  52 +        * set on the buffer_head.
  53 +        */
  54 +       clear_buffer_unwritten(bh);
  55 +
  56 +       /*
  57          * New blocks allocate and/or writing to uninitialized extent
  58          * will possibly result in updating i_data, so we take
  59          * the write lock of i_data_sem, and call get_blocks()