[GNAT 3.15p] Unexpected exception in Protected_Entry_Call

[Florian Weimer <fw@deneb.enyo.de>]

I'm seeing a strange exception raised by
System.Tasking.Protected_Objects.Operations.Protected_Entry_Call,
in this code:

      if Ceiling_Violation then

         --  Failed ceiling check

         Initialization.Undefer_Abort (Self_ID);
         raise Program_Error;
      end if;

The exception is apparently triggered by a simple conditional entry
call which is cancelled.  So far, I've only seen this issue on SMP
systems (more precisely: Linux/i386 and Linux/AMD64 (with 32-bit
userland) with NPTL).

The strange thing is that I don't use any fancy priorities, so I'm
surprised that the run-time system detects a ceiling violation.