Teach the call_time trace to notice when the trace dies (non-SMP system)

The call_time trace is a special kind of tracing that requires
a tracer process just like ordinary call trace, but it never
actually sends anything to the tracer. It merely use the existence
of a trace process (and call trace flags) as an indication that
call_time tracing is active for the process.

If the tracer dies in a non-SMP run-time system, processes with
call_time tracing would not notice that the tracer had
died. Furthermore, if the set_on_spawn flag was active, the dead
tracer could be propagaged to newly spawned processes.

Before accumulating trace information in a non-SMP system, always
validate the tracer process. (In an SMP system, a reference to a
dead tracer will be cleared away each time a process is scheduled.)

While we could put all of the new code beam_bp.c, we have chosen to
make a function call from beam_bp.c to a function in erl_trace.c for
clarity's sake and to ease further maintenance. In the future, we
might want to handle tracing in more similar ways in the SMP and
non-SMP system.

1 files changed, 3 insertions, 2 deletions

diff --git a/erts/emulator/beam/beam_bp.c b/erts/emulator/beam/beam_bp.c
index 49a34ab4ad..4e711c89e0 100644
--- a/erts/emulator/beam/beam_bp.c
+++ b/erts/emulator/beam/beam_bp.c
@@ -642,7 +642,7 @@ erts_generic_breakpoint(Process* c_p, BeamInstr* I, Eterm* reg)
 	erts_smp_atomic_inc_nob(&bp->count->acount);
     }
 
-    if (bp_flags & ERTS_BPF_TIME_TRACE_ACTIVE) {
+    if (bp_flags & ERTS_BPF_TIME_TRACE_ACTIVE && erts_is_tracer_proc_valid(c_p)) {
 	Eterm w;
 	erts_trace_time_call(c_p, I, bp->time);
 	w = (BeamInstr) *c_p->cp;
@@ -730,7 +730,8 @@ erts_bif_trace(int bif_index, Process* p, Eterm* args, BeamInstr* I)
 	}
     }
     if (bp_flags & ERTS_BPF_TIME_TRACE_ACTIVE &&
-	IS_TRACED_FL(p, F_TRACE_CALLS)) {
+	IS_TRACED_FL(p, F_TRACE_CALLS) &&
+	erts_is_tracer_proc_valid(p)) {
 	BeamInstr *pc = (BeamInstr *)ep->code+3;
 	erts_trace_time_call(p, pc, bp->time);
     }