ext4: Clear the unwritten buffer_head flag after the extent is initialized

The BH_Unwritten flag indicates that the buffer is allocated on disk
but has not been written; that is, the disk was part of a persistent
preallocation area.  That flag should only be set when a get_blocks()
function is looking up a inode's logical to physical block mapping.

When ext4_get_blocks_wrap() is called with create=1, the uninitialized
extent is converted into an initialized one, so the BH_Unwritten flag
is no longer appropriate.  Hence, we need to make sure the
BH_Unwritten is not left set, since the combination of BH_Mapped and
BH_Unwritten is not allowed; among other things, it will result ext4's
get_block() to be called over and over again during the write_begin
phase of write(2).

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 13 insertions, 0 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0ac31a06422b..2a9ffd528dd1 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1149,6 +1149,7 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
         int retval;
 
         clear_buffer_mapped(bh);
+        clear_buffer_unwritten(bh);
 
         /*
          * Try to see if we can get  the block without requesting
@@ -1179,6 +1180,18 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
                 return retval;
 
         /*
+         * When we call get_blocks without the create flag, the
+         * BH_Unwritten flag could have gotten set if the blocks
+         * requested were part of a uninitialized extent.  We need to
+         * clear this flag now that we are committed to convert all or
+         * part of the uninitialized extent to be an initialized
+         * extent.  This is because we need to avoid the combination
+         * of BH_Unwritten and BH_Mapped flags being simultaneously
+         * set on the buffer_head.
+         */
+        clear_buffer_unwritten(bh);
+
+        /*
          * New blocks allocate and/or writing to uninitialized extent
          * will possibly result in updating i_data, so we take
          * the write lock of i_data_sem, and call get_blocks()