On Tue, Apr 17, 2012 at 08:01:48AM -0700, Linus Torvalds wrote: > On Mon, Apr 16, 2012 at 10:25 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > > A bunch of endianness fixes plus a patch from bfields untangling > > dependencies between vfs and nfsd trees; in principle, we could keep it > > in nfsd tree (along with a bunch of followups that definitely belong there), > > but Miklos' stuff in fs/namei.c steps fairly close to it and overlayfs > > and unionfs series - even closer, so that would create serious PITA for > > both, whichever tree it would sit in. > > Why is that double mutex taking in vfs_rename_other() safe from ABBA? > > We aren't guaranteed to hold the s_vfs_rename_mutex, since the parent > directories may be the same. > > And yes, we hold the i_mutex on that shared parent, but the inodes may > exist (hardlinked) in another directory, so another rename could be > doing the i_mutex in the reverse order. > > Maybe there is some reason why that double lock is safe, but I don't > see it, and I want it clearly documented. So I'm not pulling this. Ugh, no, I think you're right: rename A/a->A/b rename B/b->B/b where A/a and B/a are the same file, and A/b and B/b are the same file, can result in the first rename holding the lock on A and a and waiting on b, and the second holding the lock on B and b and waiting on a. --b. -- 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
