Segfault during a big messy rebase

I was in the middle of a big messy rebase when the following happened:

$ git rebase --continue /usr/local/Cellar/git/2.9.0/libexec/git-core/git-rebase--interactive: line 238: 60305 Segmentation fault: 11 "$@" Could not commit staged changes.

And then I tried:

$ git rebase --abort fatal: Unable to create '/Users/greg/my-project/.git/MERGE_RR.lock': File exists.

Another git process seems to be running in this repository, e.g. an editor opened by 'git commit'. Please make sure all processes are terminated then try again. If it still fails, a git process may have crashed in this repository earlier: remove the file manually to continue.

Then I ran:

$ rm .git/MERGE_RR.lock $ git rebase --abort No rebase in progress?

Which left the branch in a kind of half-rebased limbo, and my only option was to put it out of its misery and delete it. Fortunately I had backed up my work to a different branch, so recovery was not a problem.

I don't know where to look inside Git for diagnostic logs; let me know if there's anything I can add to help track down the issue.