I do not expect this to be a winning answer, but it is a fairly unusual situation.
Mentioning in case someone other than me runs into it.
Today I got the "waiting for lock on repository" on an hg push command.
When I killed the hung hg command I could see no .hg/store/lock
When I looked for .hg/store/lock while the command was hung, it existed. But the lockfile was deleted when the hg command was killed.
When I went to the target of the push, and executed hg pull, no problem.
Eventually I realized that the process ID on the hg push was lock waiting message was changing each time. It turns out that the "hg push" was hanging waiting for a lock held by itself (or possibly a subprocess, I did not investigate further).
It turns out that the two workspaces, let's call them A and B, had .hg trees shared by symlink:
A/.hg --symlinked-to--> B/.hg
This is NOT a good thing to do with Mercurial. Mercurial does not understand the concept of two workspaces sharing the same repository. I do understand, however, how somebody coming to Mercurial from another VCS might want this (Perforce does, although not a DVCS; the Bazaar DVCS reportedly can do so). I am surprised that a symlinked REP-ROOT/.hg works at all, although it seems to except for this push.