On Fri, Jan 18, 2013 at 01:00:38PM +0100, Jan Kara wrote: > 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. > > Reviewed-by: Zheng Liu <wenqing.lz@xxxxxxxxxx> > Signed-off-by: Jan Kara <jack@xxxxxxx> Sorry for not noticing this earlier, but this patch is causing a regression. It is loading to test 113 failing when dioread_nolock is used: 113 [ 47.619363] EXT4-fs error (device vdb): ext4_convert_unwritten_extents_endio:3411: i node #10951: comm kworker/u:0: Written extent modified before IO finished: extent logical block 1024, len 1024; IO logical block 1024, len 127 [ 47.619363] [ 47.623239] EXT4-fs warning (device vdb): ext4_convert_unwritten_extents:4522: inode #10951: block 1024: len 127: ext4_ext_map_blocks returned -5 [ 47.628975] EXT4-fs (vdb): failed to convert unwritten extents to written extents -- potenti al data loss! (inode 10951, offset 4194304, size 520192, error -5) As a result, I am considering whether or not I should to drop the following patches from the ext4 tree: e63dd9c ext4: disable merging of uninitialized extents de39534 ext4: remove unnecessary wait for extent conversion in ext4_fallocate() 37bf0a8 ext4: ext4_split_extent should take care of extent zeroout I know that these patches fix other potential races which causes data loss, but they've been around for a while, and in practice seem to be relatively rarely hit. Jan, Dmitry, any chance you can take a look at this, and give me suggestions about how to proceed at this point? Thanks, - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
