Re: v2.15.0-rc2 ref deletion bug

On Tue, Oct 24, 2017 at 01:05:00PM +0200, Michael Haggerty wrote:

quoted

I'd expect one of:

  1. We delete "foo" before updating "foo/bar", and we end up with a
     single ref.

I don't think that this is possible in the general case in a single
transaction. The problem is that the code would need to take locks

    refs/tags/foo.lock
    refs/tags/foo/bar.lock

But the latter couldn't coexist with the loose reference file

    refs/tags/foo

, which might already exist.

Yeah, you're right. I was thinking of the opposite case (where you
could create "foo.lock" even though "foo/bar" exists), but this one is
impossible with filesystem semantics.

It is only imaginable to do this in a single transaction if you pack and
prune `refs/tags/foo` first, to get the loose reference out of the way,
before executing the transaction. Even then, you would have to beware of
a race where another process writes a loose version of `refs/tags/foo`
between the time that `pack-refs` prunes it and the time that the
transaction obtains the lock again.

Yeah, it's probably better to avoid playing games here. Moving to a
non-filesystem storage backend would just make the problem go away.

-Peff