crash in NFSv4 automount code

Issue

• Every time a user logs in, there's a kernel panic.
• The home directory layout is NFSv4 with each user's dir bind mounted from a separate export.
• RHEL 6.1 and 6.2 work fine.
• RHEL 6.3 does not crash, however ssh rsa logins fail until the user (as root) cats a file (seemingly any file) from their home directory, after which ssh rsa logins succeed.
• An strace sshd shows the open() of the users authorized_keys file failing with EACCES in the first case, and succeeding in the second.
• RHEL 6.4 operates identically to 6.3, except that instead of EACCES you get a panic.