12771 11909 re-introduced lockstat panic

@@ -492,10 +492,11 @@
         lock
         cmpxchgq %rdx, (%rdi)                   /* try to drop read lock */
         jnz     rw_exit_wakeup
 .rw_read_exit_lockstat_patch_point:
         ret
+        movq    %gs:CPU_THREAD, %rcx            /* rcx = thread ptr */
         movq    %rdi, %rsi                      /* rsi = lock ptr */
         movl    $LS_RW_EXIT_RELEASE, %edi
         movl    $RW_READER, %edx
         jmp     lockstat_wrapper_arg
 .rw_not_single_reader: