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.

3 files changed, 23 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);
     }
diff --git a/erts/emulator/beam/erl_trace.c b/erts/emulator/beam/erl_trace.c
index 6978a5f11a..305058ceff 100644
--- a/erts/emulator/beam/erl_trace.c
+++ b/erts/emulator/beam/erl_trace.c
@@ -151,6 +151,11 @@ do { \
     message dispatcher thread takes care of that). */
 #define ERTS_GET_TRACER_REF(RES, TPID, TRACEE_FLGS) \
 do { (RES) = (TPID); } while(0)
+int
+erts_is_tracer_proc_valid(Process* p)
+{
+    return 1;
+}
 #else
 #define ERTS_NULL_TRACER_REF NULL
 #define ERTS_TRACER_REF_TYPE Process *
@@ -163,6 +168,20 @@ do { \
 	return; \
     } \
 } while (0)
+int
+erts_is_tracer_proc_valid(Process* p)
+{
+    Process* tracer;
+
+    tracer = erts_proc_lookup(ERTS_TRACER_PROC(p));
+    if (tracer && ERTS_TRACE_FLAGS(tracer) & F_TRACER) {
+	return 1;
+    } else {
+	ERTS_TRACER_PROC(p) = NIL;
+	ERTS_TRACE_FLAGS(p) = ~TRACEE_FLAGS;
+	return 0;
+    }
+}
 #endif
 
 static Uint active_sched;
diff --git a/erts/emulator/beam/erl_trace.h b/erts/emulator/beam/erl_trace.h
index 853c6cb0d8..4f2c70d6e7 100644
--- a/erts/emulator/beam/erl_trace.h
+++ b/erts/emulator/beam/erl_trace.h
@@ -39,6 +39,7 @@ void erts_change_default_tracing(int setflags, Uint *flagsp, Eterm *tracerp);
 void erts_get_default_tracing(Uint *flagsp, Eterm *tracerp);
 void erts_set_system_monitor(Eterm monitor);
 Eterm erts_get_system_monitor(void);
+int erts_is_tracer_proc_valid(Process* p);
 
 #ifdef ERTS_SMP
 void erts_check_my_tracer_proc(Process *);