> Is there any particular reason not to merge Charles-François's reinit_locks.diff?
> 
> Reinitialising all locks to unlocked after a fork seems the only sane option.

I agree with this. 
I haven't looked at the patch very closely. I think perhaps each lock
could have an optional callback for specific code to be run after
forking, but that may come in another patch.
(this would allow to make e.g. the C RLock fork-safe)