[diagnostic] cache_lock: blocked on 0xe29c3b08 ""

[dpwalters at carolina.rr.com]

Following [diagnostic] cache_lock: blocked on 0xe29c3b08 "quota.user" in dmesg and /var/log/messages. System almost completely hangs; I am unable to create a new shell, enter commands, etc (or even reboot). Kernel options are SMP, IO_APIC, and QUOTA. The bug appears to manifest itself after applying userquota to a filesystem, mounting it, and then issuing a few commands like mkdir/chmod/etc on it. System is a dual processor Opteron 248.