ext4: serialize fallocate with ext4_convert_unwritten_extents

Fallocate should wait for pended ext4_convert_unwritten_extents()
otherwise following race may happen:

ftruncate( ,12288);
fallocate( ,0, 4096)
io_sibmit( ,0, 4096); /* Write to fallocated area, split extent if needed */
fallocate( ,0, 8192); /* Grow extent and broke assumption about extent */

Later kwork completion will do:
 ->ext4_convert_unwritten_extents (0, 4096)
   ->ext4_map_blocks(handle, inode, &map, EXT4_GET_BLOCKS_IO_CONVERT_EXT);
    ->ext4_ext_map_blocks() /* Will find new extent:  ex = [0,2] !!!!!! */
      ->ext4_ext_handle_uninitialized_extents()
        ->ext4_convert_unwritten_extents_endio()
        /* convert [0,2] extent to initialized, but only[0,1] was written */

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 3 insertions, 0 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 1c94cca35ed1..c2789271e7b4 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4428,6 +4428,9 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
          */
         if (len <= EXT_UNINIT_MAX_LEN << blkbits)
                 flags |= EXT4_GET_BLOCKS_NO_NORMALIZE;
+
+        /* Prevent race condition between unwritten */
+        ext4_flush_unwritten_io(inode);
 retry:
         while (ret >= 0 && ret < max_blocks) {
                 map.m_lblk = map.m_lblk + ret;