On Thu 31-01-13 11:47:23, Dmitry Monakhov wrote: > On Thu, 24 Jan 2013 13:49:45 +0400, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote: > > On Fri, 18 Jan 2013 13:00:38 +0100, Jan Kara <jack@xxxxxxx> 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 > > As we already discussed your idea is 100% correct, but even with > > what patch I still able to trigger situation where split it required. > > I've got following error with this patch applied on top of 7f5118629f7 > > EXT4-fs error (device dm-3): ext4_convert_unwritten_extents_endio:3411: > > inode #12: comm kworker/u:4: Written extent modified before IO finished: > > extent logical block 1379787, len 64; IO logical block 1379787, len 21 > > > > ------------[ cut here ]------------ > > WARNING: at fs/ext4/extents.c:4518 > > ext4_convert_unwritten_extents+0x149/0x210 [ext4]() > OK I've found it. I'm a bit disappointed, it is even not a race > condition, but simple corruption. > Patch is available here: http://article.gmane.org/gmane.comp.file-systems.ext4/36762 > link for sain mailer client: <1359617098-18451-1-git-send-email-dmonakhov@xxxxxxxxxx> > After this bug was fixed it is safe to apply both Jan's patches: > [PATCH 04/12] ext4: Disable merging of uninitialized extents > [PATCH 05/12] ext4: Remove unnecessary wait for extent conversion in ext4_fallocate() > At least it survives after all my tests. Thanks for debugging this. I was looking into the code but it didn't come to my mind what happens when ext4_ext_split() fails. > BTW: It is appeared that ext4_debug() infrastructure is almost unusable > because based on printk() instead of light-wait event tracing infrastructure. > I'm now work on patch-set which fix that. That would be certainly welcome. ext4_debug() infrastructure comes from times when tracing didn't exist so we used what we could. These days it's cumbersome... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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
