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.

4 files changed, 115 insertions, 6 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 *);
diff --git a/erts/emulator/test/trace_call_time_SUITE.erl b/erts/emulator/test/trace_call_time_SUITE.erl
index 5dfa87bbee..3036d2957b 100644
--- a/erts/emulator/test/trace_call_time_SUITE.erl
+++ b/erts/emulator/test/trace_call_time_SUITE.erl
@@ -33,7 +33,7 @@
 %% Exported end user tests
 
 -export([seq/3, seq_r/3]).
--export([loaded/1, a_function/1, a_called_function/1, dec/1, nif_dec/1]).
+-export([loaded/1, a_function/1, a_called_function/1, dec/1, nif_dec/1, dead_tracer/1]).
 
 -define(US_ERROR, 10000).
 -define(R_ERROR, 0.8).
@@ -89,7 +89,7 @@ all() ->
 	true -> [not_run];
 	false ->
 	    [basic, on_and_off, info, pause_and_restart, scheduling,
-	     combo, bif, nif, called_function]
+	     combo, bif, nif, called_function, dead_tracer]
     end.
 
 groups() -> 
@@ -470,6 +470,92 @@ called_function(Config) when is_list(Config) ->
     ?line P = erlang:trace_pattern({'_','_','_'}, false, [call_time]),
     ok.
 
+%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+dead_tracer(Config) when is_list(Config) ->
+    Self = self(),
+    FirstTracer = tracer(),
+    StartTracing = fun() -> turn_on_tracing(Self) end,
+    tell_tracer(FirstTracer, StartTracing),
+    [1,2,3,4,5,6,7,8] = seq(1, 8, fun(I) -> I + 1 end),
+    Ref = erlang:monitor(process, FirstTracer),
+    FirstTracer ! quit,
+    receive
+	{'DOWN',Ref,process,FirstTracer,normal} ->
+	    ok
+    end,
+    erlang:yield(),
+
+    %% Collect and check that we only get call_time info for the current process.
+    Info1 = collect_all_info(),
+    [] = other_than_self(Info1),
+    io:format("~p\n", [Info1]),
+
+    %% Note that we have not turned off tracing for the current process,
+    %% but that the tracer has terminated. No more call_time information should be recorded.
+    [1,2,3] = seq(1, 3, fun(I) -> I + 1 end),
+    [] = collect_all_info(),
+
+    %% When we start a second tracer process, that tracer process must
+    %% not inherit the tracing flags and the dead tracer (even though
+    %% we used set_on_spawn).
+    SecondTracer = tracer(),
+    tell_tracer(SecondTracer, StartTracing),
+    Seq20 = lists:seq(1, 20),
+    Seq20 = seq(1, 20, fun(I) -> I + 1 end),
+    Info2 = collect_all_info(),
+    io:format("~p\n", [Info2]),
+    [] = other_than_self(Info2),
+    SecondTracer ! quit,
+
+    ok.
+
+other_than_self(Info) ->
+    [{Pid,MFA} || {MFA,[{Pid,_,_,_}]} <- Info,
+		  Pid =/= self()].
+
+tell_tracer(Tracer, Fun) ->
+    Tracer ! {execute,self(),Fun},
+    receive
+	{Tracer,executed} ->
+	    ok
+    end.
+
+tracer() ->
+    spawn_link(fun Loop() ->
+		      receive
+			  quit ->
+			      ok;
+			  {execute,From,Fun} ->
+			      Fun(),
+			      From ! {self(),executed},
+			      Loop()
+		      end
+	      end).
+
+turn_on_tracing(Pid) ->
+    _ = erlang:trace(Pid, true, [call,set_on_spawn]),
+    _ = erlang:trace_pattern({?MODULE,'_','_'}, true, [call_time]),
+    _ = now(),
+    ok.
+
+collect_all_info() ->
+    collect_all_info([{?MODULE,F,A} || {F,A} <- module_info(functions)] ++
+			 erlang:system_info(snifs)).
+
+collect_all_info([MFA|T]) ->
+    CallTime = erlang:trace_info(MFA, call_time),
+    erlang:trace_pattern(MFA, restart, [call_time]),
+    case CallTime of
+	{call_time,false} ->
+	    collect_all_info(T);
+	{call_time,[]} ->
+	    collect_all_info(T);
+	{call_time,[_|_]=List} ->
+	    [{MFA,List}|collect_all_info(T)]
+    end;
+collect_all_info([]) -> [].
+
 %%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %%% The Tests
 %%%
@@ -478,7 +564,6 @@ called_function(Config) when is_list(Config) ->
 %% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 %% Local helpers
 
-
 load_nif(Config) ->
     ?line Path = ?config(data_dir, Config),
     ?line ok = erlang:load_nif(filename:join(Path,"trace_nif"), 0).
@@ -602,8 +687,11 @@ collect(A, Ref) ->
     end.
 
 setup() ->
+    setup([]).
+
+setup(Opts) ->
     Pid = spawn_link(fun() -> loop() end),
-    ?line 1 = erlang:trace(Pid, true, [call]),
+    1 = erlang:trace(Pid, true, [call|Opts]),
     Pid.
 
 execute(Pids, Mfa) when is_list(Pids) ->