Commit 60d4616f authored Oct 05, 2012 by Dmitry Monakhov Committed by Theodore Ts'o Oct 05, 2012

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>

parent c278531d

fs/ext4/extents.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -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;

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