erts: Do tracer liveness check on current tracer

This fixes a fault introduced in 19.0 where an invalid
tracer would block setting of a new tracer on a process.

2 files changed, 35 insertions, 7 deletions

diff --git a/erts/emulator/beam/erl_bif_trace.c b/erts/emulator/beam/erl_bif_trace.c
index 66e5146da0..96275eb228 100644
--- a/erts/emulator/beam/erl_bif_trace.c
+++ b/erts/emulator/beam/erl_bif_trace.c
@@ -512,7 +512,7 @@ start_trace(Process *c_p, ErtsTracer tracer,
             && !ERTS_TRACER_COMPARE(ERTS_TRACER(port), tracer)) {
             /* This tracee is already being traced, and not by the
              * tracer to be */
-            if (erts_is_tracer_enabled(tracer, common)) {
+            if (erts_is_tracer_enabled(ERTS_TRACER(port), common)) {
                 /* The tracer is still in use */
                 return 1;
             }
@@ -715,8 +715,8 @@ Eterm erts_internal_trace_3(BIF_ALIST_3)
 		    Process* tracee_p = erts_pix2proc(i);
 		    if (! tracee_p) 
 			continue;
-                    start_trace(p, tracer, &tracee_p->common, on, mask);
-		    matches++;
+                    if (!start_trace(p, tracer, &tracee_p->common, on, mask))
+                        matches++;
 		}
 	    }
 	    if (ports || mods) {
@@ -730,8 +730,8 @@ Eterm erts_internal_trace_3(BIF_ALIST_3)
 		    state = erts_atomic32_read_nob(&tracee_port->state);
 		    if (state & ERTS_PORT_SFLGS_DEAD)
 			continue;
-                    start_trace(p, tracer, &tracee_port->common, on, mask);
-                    matches++;
+                    if (!start_trace(p, tracer, &tracee_port->common, on, mask))
+                        matches++;
 		}
 	    }
 	}
diff --git a/erts/emulator/test/trace_SUITE.erl b/erts/emulator/test/trace_SUITE.erl
index da6a6bdea4..f846b0f4b9 100644
--- a/erts/emulator/test/trace_SUITE.erl
+++ b/erts/emulator/test/trace_SUITE.erl
@@ -30,7 +30,7 @@
 	 procs_trace/1, dist_procs_trace/1, procs_new_trace/1,
 	 suspend/1, mutual_suspend/1, suspend_exit/1, suspender_exit/1,
 	 suspend_system_limit/1, suspend_opts/1, suspend_waiting/1,
-	 new_clear/1, existing_clear/1,
+	 new_clear/1, existing_clear/1, tracer_die/1,
 	 set_on_spawn/1, set_on_first_spawn/1, cpu_timestamp/1,
 	 set_on_link/1, set_on_first_link/1,
 	 system_monitor_args/1, more_system_monitor_args/1,
@@ -54,7 +54,7 @@ all() ->
      send_trace, procs_trace, dist_procs_trace, suspend,
      mutual_suspend, suspend_exit, suspender_exit,
      suspend_system_limit, suspend_opts, suspend_waiting,
-     new_clear, existing_clear, set_on_spawn,
+     new_clear, existing_clear, tracer_die, set_on_spawn,
      set_on_first_spawn, set_on_link, set_on_first_link,
      system_monitor_args,
      more_system_monitor_args, system_monitor_long_gc_1,
@@ -1636,6 +1636,34 @@ existing_clear(Config) when is_list(Config) ->
 
     ok.
 
+%% Test that erlang:trace/3 can be called on processes where the
+%% tracer has died. OTP-13928
+tracer_die(Config) when is_list(Config) ->
+    Proc = spawn(fun receiver/0),
+
+    Tracer = spawn(fun receiver/0),
+    timer:sleep(1),
+    N = erlang:trace(existing, true, [send, {tracer, Tracer}]),
+    {flags, [send]} = erlang:trace_info(Proc, flags),
+    {tracer, Tracer} = erlang:trace_info(Proc, tracer),
+    exit(Tracer, die),
+
+    Tracer2 = spawn(fun receiver/0),
+    timer:sleep(1),
+    N = erlang:trace(existing, true, [send, {tracer, Tracer2}]),
+    {flags, [send]} = erlang:trace_info(Proc, flags),
+    {tracer, Tracer2} = erlang:trace_info(Proc, tracer),
+    exit(Tracer2, die),
+
+    Tracer3 = spawn(fun receiver/0),
+    timer:sleep(1),
+    1 = erlang:trace(Proc, true, [send, {tracer, Tracer3}]),
+    {flags, [send]} = erlang:trace_info(Proc, flags),
+    {tracer, Tracer3} = erlang:trace_info(Proc, tracer),
+    exit(Tracer3, die),
+
+    ok.
+
 %% Test that an invalid flag cause badarg
 bad_flag(Config) when is_list(Config) ->
     %% A bad flag could deadlock the SMP emulator in erts-5.5