My test system, which I use to follow current github master builds, has a problem whereby s2s will lock up. It seems to happen with gmail.com federation. It also seems to happen once two incoming sessions are established. I am attaching a thread dump while s2s is locked.
I am currently running a development build with this change and no s2s lockups yet, knock on wood!
Sigh, my test system (recent master) wedged up s2s again, reopening.
PR has been merged and I am testing it now.
Gonna mark this as resolved for now, just to get it back included in the 3.10 RC release notes. Can reopen if I hit it again