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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>
This commit is contained in:
Dmitry Monakhov 2012-10-05 11:32:02 -04:00 committed by Theodore Ts'o
parent c278531d39
commit 60d4616f3d
1 changed files with 3 additions and 0 deletions
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3
fs/ext4/extents.c
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@ -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;