Enabling CONFIG_CPUMASK_OFFSTACK in stock kernel 3.18.0 causes the staging ptlrpc module to emit the message
LustreError: 1203:0:(service.c:2796:ptlrpc_hr_init()) ASSERTION( hrp->hrp_nthrs > 0 ) failed:
followed by a backtrace and kernel lockup upon loading. I'll attach my dmesg dump and the .config file I used. I picked version 2.4.0 above as there doesn't seem to be anyway to indicate the staging client version.