On Wed, 10 Jul 2013 17:26:21 -0400 "J. Bruce Fields" <bfields@xxxxxxxxxx> wrote: > On Wed, Jul 10, 2013 at 01:38:53PM +1000, Dave Chinner wrote: > > On Tue, Jul 09, 2013 at 10:40:59PM -0400, J. Bruce Fields wrote: > > > On Wed, Jul 10, 2013 at 12:09:21PM +1000, Dave Chinner wrote: > > > > Sure. I'd prefer ordering by inode number, because then ordering is > > > > deterministic rather than being dependent on memory allocation > > > > results. It makes forensic analysis of deadlocks and corruptions > > > > easier because you can look at on-disk structures and accurately > > > > predict locking behaviour and therefore determine the order of > > > > operations that should occur. With lock ordering determined by > > > > memory addresses, you can't easily predict the lock ordering two > > > > particular inodes might take from one operation to another. > > > > > > Hm, OK, not having done this I don't have a good feeling for how > > > important that is, but I can take your word for it. > > > > > > But the ext4 code actually originally used i_ino order and was changed > > > by 03bd8b9b896c8e "ext4: move_extent code cleanup", possibly on Linus's > > > suggestion?: > > > > > > http://mid.gmane.org/<CA+55aFwdh_QWG-R2FQ71kDXiNYZ04qPANBsY_PssVUwEBH4uSw@xxxxxxxxxxxxxx> > > > > > > "And the only sane order is comparing inode pointers, not inode > > > numbers like ext4 apparently does." > > > > Interesting. What has worked for the last 20 years must be wrong if > > Linus says so ;) > > > > > > > > (Uh, I thought I also remembered some rationale but can't dig up the > > > email now.) > > > > Probably duplicate inode numbers on inodes in different filesystems. > > But rename doesn't allow that, and I don't we ever want to allow > > arbitrary nested inode locking across superblocks. Hence I can't > > think of a reason why it's a problem... > > I have some vague memory the argument was rather that inode numbers > could fail to be unique within a fs due to bugs, but I may be making > that up. I've got no strong opinion here. > There are also legitimate cases where inode numbers can collide, particularly on network filesystems. That's one of the main reasons we have iget5_locked(). One possibility might be to order by i_ino first, and then fall back to using the inode pointer value if they are equal. > > FWIW - gfs2 does multiple glock locking similar to XFS inode locking > > - it sorts the locks in lock number order and the locks them all one > > at a time... > ... > > A quick grep shows lock_2_inodes() in fs/ubifs/dir.c. I don't see > > any other obvious ones. > > OK. I'll put off reposting till I've had a chance to look at those > cases more carefully.... Thanks for the review! > > --b. > -- > To unsubscribe from this list: send the line "unsubscribe linux-nfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- Jeff Layton <jlayton@xxxxxxxxxxxxxxx> -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
