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

(cherry picked from commit 2a8964d63d50dd2d65d71d342bc7fb6ef4117614)

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 57923cc150c666d0cb7a86b29a037c9f5e23b85b..725f20ab62083889a5c3001dc7df4afd74049dda 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1076,6 +1076,7 @@ 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
@@ -1105,6 +1106,18 @@ int ext4_get_blocks_wrap(handle_t *handle, struct inode *inode, sector_t block,
        if (retval > 0 && buffer_mapped(bh))
                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