take-read-lock-during-overwrite-case.patch

   1 ext4: Take read lock during overwrite case.
   2
   3 From: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
   4
   5 When we are overwriting a file and not actually allocating new file system
   6 blocks we need to take only the read lock on i_data_sem.
   7
   8 Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
   9 ---
  10
  11  fs/ext4/inode.c |   32 ++++++++++++++++++++++++--------
  12  1 files changed, 24 insertions(+), 8 deletions(-)
  13
  14
  15 diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
  16 index a7eb8bb..89cd353 100644
  17 --- a/fs/ext4/inode.c
  18 +++ b/fs/ext4/inode.c
  19 @@ -901,11 +901,31 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
  20                         int create, int extend_disksize)
  21  {
  22         int retval;
  23 -       if (create) {
  24 -               down_write((&EXT4_I(inode)->i_data_sem));
  25 +       /*
  26 +        * Try to see if we can get  the block without requesting
  27 +        * for new file system block.
  28 +        */
  29 +       down_read((&EXT4_I(inode)->i_data_sem));
  30 +       if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
  31 +               retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
  32 +                               bh, 0, 0);
  33         } else {
  34 -               down_read((&EXT4_I(inode)->i_data_sem));
  35 +               retval = ext4_get_blocks_handle(handle,
  36 +                               inode, block, max_blocks, bh, 0, 0);
  37         }
  38 +       up_read((&EXT4_I(inode)->i_data_sem));
  39 +       if (!create || (retval > 0))
  40 +               return retval;
  41 +
  42 +       /*
  43 +        * We need to allocate new blocks which will result
  44 +        * in i_data update
  45 +        */
  46 +       down_write((&EXT4_I(inode)->i_data_sem));
  47 +       /*
  48 +        * We need to check for EXT4 here because migrate
  49 +        * could have changed the inode type in between
  50 +        */
  51         if (EXT4_I(inode)->i_flags & EXT4_EXTENTS_FL) {
  52                 retval =  ext4_ext_get_blocks(handle, inode, block, max_blocks,
  53                                 bh, create, extend_disksize);
  54 @@ -913,11 +933,7 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
  55                 retval = ext4_get_blocks_handle(handle, inode, block,
  56                                 max_blocks, bh, create, extend_disksize);
  57         }
  58 -       if (create) {
  59 -               up_write((&EXT4_I(inode)->i_data_sem));
  60 -       } else {
  61 -               up_read((&EXT4_I(inode)->i_data_sem));
  62 -       }
  63 +       up_write((&EXT4_I(inode)->i_data_sem));
  64         return retval;
  65  }
  66