Ensure is_process_alive() and process_info() respect signal order

The reply signal sent as a result of a call to the is_process_alive() or
the process_info() BIFs could pass before other signals sent between the
involved processes. That is, the reply signals could be delivered too
early.

3 files changed, 22 insertions, 5 deletions

diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 96f399fbbe..5c58c68369 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -1212,7 +1212,10 @@ process_info_bif(Process *c_p, Eterm pid, Eterm opt, int always_wrap, int pi2)
         goto send_signal;
     }
 
-    ERTS_BIF_PREP_RET(ret, res);
+    if (c_p == rp || !ERTS_PROC_HAS_INCOMING_SIGNALS(c_p))
+        ERTS_BIF_PREP_RET(ret, res);
+    else
+        ERTS_BIF_PREP_HANDLE_SIGNALS_RETURN(ret, c_p, res);
 
 done:
 
@@ -3570,7 +3573,10 @@ BIF_RETTYPE erts_internal_is_process_alive_2(BIF_ALIST_2)
 {
     if (!is_internal_pid(BIF_ARG_1) || !is_internal_ordinary_ref(BIF_ARG_2))
         BIF_ERROR(BIF_P, BADARG);
-    erts_proc_sig_send_is_alive_request(BIF_P, BIF_ARG_1, BIF_ARG_2);
+    if (!erts_proc_sig_send_is_alive_request(BIF_P, BIF_ARG_1, BIF_ARG_2)) {
+        if (ERTS_PROC_HAS_INCOMING_SIGNALS(BIF_P))
+            ERTS_BIF_HANDLE_SIGNALS_RETURN(BIF_P, am_ok);
+    }
     BIF_RET(am_ok);
 }
 
diff --git a/erts/emulator/beam/erl_proc_sig_queue.c b/erts/emulator/beam/erl_proc_sig_queue.c
index d475a0a634..5d7e5ff999 100644
--- a/erts/emulator/beam/erl_proc_sig_queue.c
+++ b/erts/emulator/beam/erl_proc_sig_queue.c
@@ -1528,7 +1528,7 @@ erts_proc_sig_send_group_leader(Process *c_p, Eterm to, Eterm gl, Eterm ref)
         group_leader_reply(c_p, c_p->common.id, ref, 0);
 }
 
-void
+int
 erts_proc_sig_send_is_alive_request(Process *c_p, Eterm to, Eterm ref)
 {
     ErlHeapFragment *hfrag;
@@ -1562,13 +1562,16 @@ erts_proc_sig_send_is_alive_request(Process *c_p, Eterm to, Eterm ref)
                                                   ERTS_SIG_Q_TYPE_UNDEFINED,
                                                   0);
 
-    if (proc_queue_signal(c_p, to, (ErtsSignal *) mp, ERTS_SIG_Q_OP_IS_ALIVE))
+    if (proc_queue_signal(c_p, to, (ErtsSignal *) mp, ERTS_SIG_Q_OP_IS_ALIVE)) {
         (void) maybe_elevate_sig_handling_prio(c_p, to);
+        return !0;
+    }
     else {
         /* It wasn't alive; reply to ourselves... */
         mp->next = NULL;
         mp->data.attached = ERTS_MSG_COMBINED_HFRAG;
         erts_queue_message(c_p, ERTS_PROC_LOCK_MAIN, mp, msg, am_system);
+        return 0;
     }
 }
 
diff --git a/erts/emulator/beam/erl_proc_sig_queue.h b/erts/emulator/beam/erl_proc_sig_queue.h
index 6b065a7add..fa57fdf04b 100644
--- a/erts/emulator/beam/erl_proc_sig_queue.h
+++ b/erts/emulator/beam/erl_proc_sig_queue.h
@@ -180,6 +180,10 @@ void erts_proc_sig_hdbg_check_in_queue(struct process *c_p, char *what,
 
 struct dist_entry_;
 
+#define ERTS_PROC_HAS_INCOMING_SIGNALS(P)                               \
+    (!!(erts_atomic32_read_nob(&(P)->state)                             \
+        & (ERTS_PSFLG_SIG_Q|ERTS_PSFLG_SIG_IN_Q)))
+
 /*
  * Send operations of currently supported process signals follow...
  */
@@ -506,8 +510,12 @@ erts_proc_sig_send_group_leader(Process *c_p, Eterm to, Eterm gl,
  *                              message to the sending
  *                              process (i.e., c_p).
  *
+ * @returns                     A value != 0 if the request
+ *                              was sent; otherwise, 0. If
+ *                              the request was not sent the
+ *                              process was non-existing.
  */
-void
+int
 erts_proc_sig_send_is_alive_request(Process *c_p, Eterm to,
                                     Eterm ref);