-;;;; OS X doesn't like these being at all, and gives us a SIGSEGV
-;;;; instead of using the Mach expection system! Our or OS X's fault?
-;;;; :/
-
+;;;; FIXME: OS X 10.4 doesn't like these being at all, and gives us a SIGSEGV
+;;;; instead of using the Mach expection system! 10.5 on the other tends to
+;;;; lose() where with interrupt already pending. :/
+;;;;
+;;;; FIXME: This test also occasionally hangs on Linux/x86-64 at least. The
+;;;; common feature is one thread in gc_stop_the_world, and another trying to
+;;;; signal_interrupt_thread, but both (apparently) getting EAGAIN repeatedly.
+;;;; Exactly how or why this is happening remains under investigation -- but
+;;;; it seems plausible that the fast timers simply fill up the interrupt
+;;;; queue completely. (On some occasions the process unwedges itself after
+;;;; a few minutes, but not always.)
+;;;;
+;;;; FIXME: Another failure mode on Linux: recursive entries to
+;;;; RUN-EXPIRED-TIMERS blowing the stack.
+#+nil