Commit ec22ba8e authored Mar 04, 2013 by Dmitry Monakhov Committed by Theodore Ts'o Mar 04, 2013

ext4: disable merging of uninitialized extents

Derived from Jan's patch:http://permalink.gmane.org/gmane.comp.file-systems.ext4/36470



Merging of uninitialized extents creates all sorts of interesting race
possibilities when writeback / DIO races with fallocate. Thus
ext4_convert_unwritten_extents_endio() has to deal with a case where
extent to be converted needs to be split out first. That isn't nice
for two reasons:

1) It may need allocation of extent tree block so ENOSPC is possible.
2) It complicates end_io handling code

So we disable merging of uninitialized extents which allows us to simplify
the code. Extents will get merged after they are converted to initialized
ones.

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

parent 357b66fd

fs/ext4/extents.c

+5 −3

Original line number	Diff line number	Diff line
		@@ -1584,10 +1584,12 @@ ext4_can_extents_be_merged(struct inode inode, struct ext4_extent ex1,
		unsigned short ext1_ee_len, ext2_ee_len, max_len;

		/*
		* Make sure that either both extents are uninitialized, or
		* both are _not_.
		* Make sure that both extents are initialized. We don't merge
		* uninitialized extents so that we can be sure that end_io code has
		* the extent that was written properly split out and conversion to
		* initialized is trivial.
		*/
		if (ext4_ext_is_uninitialized(ex1) ^ ext4_ext_is_uninitialized(ex2))
		if (ext4_ext_is_uninitialized(ex1) \|\| ext4_ext_is_uninitialized(ex2))
		return 0;

		if (ext4_ext_is_uninitialized(ex1))