Merge branch 'rickard/signals/OTP-14589'

* rickard/signals/OTP-14589:
  Fix VM probes compilation
  Fix lock counting
  Fix signal order for is_process_alive
  Fix signal handling priority elevation

16 files changed, 405 insertions, 250 deletions

diff --git a/erts/emulator/beam/bif.c b/erts/emulator/beam/bif.c
index adea7d007e..232597c5b6 100644
--- a/erts/emulator/beam/bif.c
+++ b/erts/emulator/beam/bif.c
@@ -52,7 +52,6 @@ Export *erts_await_result;
 static Export await_exit_trap;
 static Export* flush_monitor_messages_trap = NULL;
 static Export* set_cpu_topology_trap = NULL;
-static Export* await_proc_exit_trap = NULL;
 static Export* await_port_send_result_trap = NULL;
 Export* erts_format_cpu_topology_trap = NULL;
 static Export dsend_continue_trap_export;
@@ -4654,42 +4653,6 @@ static BIF_RETTYPE bif_return_trap(BIF_ALIST_2)
     BIF_RET(res);
 }
 
-void
-erts_bif_prep_await_proc_exit_data_trap(Process *c_p, Eterm pid, Eterm ret)
-{
-    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_data, ret);
-}
-
-void
-erts_bif_prep_await_proc_exit_reason_trap(Process *c_p, Eterm pid)
-{
-    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p,
-                               pid, am_reason, am_undefined);
-}
-
-void
-erts_bif_prep_await_proc_exit_apply_trap(Process *c_p,
-					 Eterm pid,
-					 Eterm module,
-					 Eterm function,
-					 Eterm args[],
-					 int nargs)
-{
-    Eterm term;
-    Eterm *hp;
-    int i;
-    ASSERT(is_atom(module) && is_atom(function));
-
-    hp = HAlloc(c_p, 4+2*nargs);
-    term = NIL;
-    for (i = nargs-1; i >= 0; i--) {
-        term = CONS(hp, args[i], term);
-        hp += 2;
-    }
-    term = TUPLE3(hp, module, function, term);
-    ERTS_BIF_PREP_TRAP3_NO_RET(await_proc_exit_trap, c_p, pid, am_apply, term);
-}
-
 Export bif_return_trap_export;
 
 void erts_init_trap_export(Export* ep, Eterm m, Eterm f, Uint a,
@@ -4742,7 +4705,6 @@ void erts_init_bif(void)
     erts_format_cpu_topology_trap = erts_export_put(am_erlang,
 						    am_format_cpu_topology,
 						    1);
-    await_proc_exit_trap = erts_export_put(am_erlang,am_await_proc_exit,3);
     await_port_send_result_trap
 	= erts_export_put(am_erts_internal, am_await_port_send_result, 3);
     system_flag_scheduler_wall_time_trap
diff --git a/erts/emulator/beam/bif.h b/erts/emulator/beam/bif.h
index dca53686f4..a33421d762 100644
--- a/erts/emulator/beam/bif.h
+++ b/erts/emulator/beam/bif.h
@@ -437,67 +437,6 @@ do {					\
 	ERTS_BIF_EXITED((PROC));	\
 } while (0)
 
-/*
- * The ERTS_BIF_*_AWAIT_X_*_TRAP makros either exits the caller, or
- * sets up a trap to erlang:await_proc_exit/3.
- *
- * The caller is acquired to hold the 'main' lock on C_P. No other locks
- * are allowed to be held.
- */
-
-#define ERTS_BIF_PREP_AWAIT_X_DATA_TRAP(RET, C_P, PID, DATA)		\
-do {									\
-    erts_bif_prep_await_proc_exit_data_trap((C_P), (PID), (DATA));	\
-    (RET) = THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_PREP_AWAIT_X_REASON_TRAP(RET, C_P, PID)		\
-do {									\
-    erts_bif_prep_await_proc_exit_reason_trap((C_P), (PID));		\
-    (RET) = THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_PREP_AWAIT_X_APPLY_TRAP(RET, C_P, PID, M, F, A, AN)	\
-do {									\
-    erts_bif_prep_await_proc_exit_apply_trap((C_P), (PID),		\
-					     (M), (F), (A), (AN));	\
-    (RET) = THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_AWAIT_X_DATA_TRAP(C_P, PID, DATA)			\
-do {									\
-    erts_bif_prep_await_proc_exit_data_trap((C_P), (PID), (DATA));	\
-    return THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_AWAIT_X_REASON_TRAP(C_P, PID)				\
-do {									\
-    erts_bif_prep_await_proc_exit_reason_trap((C_P), (PID));		\
-    return THE_NON_VALUE;						\
-} while (0)
-
-#define ERTS_BIF_AWAIT_X_APPLY_TRAP(C_P, PID, M, F, A, AN)		\
-do {									\
-    erts_bif_prep_await_proc_exit_apply_trap((C_P), (PID),		\
-					     (M), (F), (A), (AN));	\
-    return THE_NON_VALUE;						\
-} while (0)
-
-void
-erts_bif_prep_await_proc_exit_data_trap(Process *c_p,
-					Eterm pid,
-					Eterm data);
-void
-erts_bif_prep_await_proc_exit_reason_trap(Process *c_p,
-					  Eterm pid);
-void
-erts_bif_prep_await_proc_exit_apply_trap(Process *c_p,
-					 Eterm pid,
-					 Eterm module,
-					 Eterm function,
-					 Eterm args[],
-					 int nargs);
-
 int erts_call_dirty_bif(ErtsSchedulerData *esdp, Process *c_p,
 			BeamInstr *I, Eterm *reg);
 
diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index 93613ac2eb..687fd39d58 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -266,6 +266,7 @@ bif erlang:demonitor/1
 bif erlang:demonitor/2
 
 bif erlang:is_process_alive/1
+bif erts_internal:is_process_alive/2
 
 bif erlang:error/1		error_1
 bif erlang:error/2		error_2
diff --git a/erts/emulator/beam/erl_bif_info.c b/erts/emulator/beam/erl_bif_info.c
index 6106cfdcfd..bdca93428e 100644
--- a/erts/emulator/beam/erl_bif_info.c
+++ b/erts/emulator/beam/erl_bif_info.c
@@ -73,6 +73,9 @@ static Export *gather_msacc_res_trap;
 static Export *gather_gc_info_res_trap;
 static Export *gather_system_check_res_trap;
 
+static Export *is_process_alive_trap;
+
+
 #define DECL_AM(S) Eterm AM_ ## S = am_atom_put(#S, sizeof(#S) - 1)
 
 static char otp_version[] = ERLANG_OTP_VERSION;
@@ -3501,34 +3504,53 @@ fun_info_mfa_1(BIF_ALIST_1)
     BIF_ERROR(p, BADARG);
 }
 
+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);
+    BIF_RET(am_ok);
+}
+
 BIF_RETTYPE is_process_alive_1(BIF_ALIST_1) 
 {
-   if(is_internal_pid(BIF_ARG_1)) {
-       Process *rp;
-
-       if (BIF_ARG_1 == BIF_P->common.id)
-	   BIF_RET(am_true);
-
-       rp = erts_proc_lookup_raw(BIF_ARG_1);
-       if (!rp) {
-	   BIF_RET(am_false);
-       }
-       else {
-	   if (erts_atomic32_read_acqb(&rp->state) & ERTS_PSFLG_EXITING)
-	       ERTS_BIF_AWAIT_X_DATA_TRAP(BIF_P, BIF_ARG_1, am_false);
-	   else
-	       BIF_RET(am_true);
-       }
-   }
-   else if(is_external_pid(BIF_ARG_1)) {
-       if(external_pid_dist_entry(BIF_ARG_1) == erts_this_dist_entry)
+    if (is_internal_pid(BIF_ARG_1)) {
+        erts_aint32_t state;
+        Process *rp;
+
+        if (BIF_ARG_1 == BIF_P->common.id)
+            BIF_RET(am_true);
+
+        rp = erts_proc_lookup_raw(BIF_ARG_1);
+        if (!rp)
+            BIF_RET(am_false);
+
+        state = erts_atomic32_read_acqb(&rp->state);
+        if (state & (ERTS_PSFLG_EXITING
+                     | ERTS_PSFLG_SIG_Q
+                     | ERTS_PSFLG_SIG_IN_Q)) {
+            /*
+             * If in exiting state, trap out and send 'is alive'
+             * request and wait for it to complete termination.
+             *
+             * If process has signals enqueued, we need to
+             * send it an 'is alive' request via its signal
+             * queue in order to ensure that signal order is
+             * preserved (we may earlier have sent it an
+             * exit signal that has not been processed yet).
+             */
+            BIF_TRAP1(is_process_alive_trap, BIF_P, BIF_ARG_1);
+        }
+
+        BIF_RET(am_true);
+    }
+
+   if (is_external_pid(BIF_ARG_1)) {
+       if (external_pid_dist_entry(BIF_ARG_1) == erts_this_dist_entry)
 	   BIF_RET(am_false); /* A pid from an old incarnation of this node */
-       else
-	   BIF_ERROR(BIF_P, BADARG);
-   }
-   else {
-      BIF_ERROR(BIF_P, BADARG);
    }
+
+   BIF_ERROR(BIF_P, BADARG);
 }
 
 BIF_RETTYPE process_display_2(BIF_ALIST_2)
@@ -5007,6 +5029,10 @@ erts_bif_info_init(void)
 	= erts_export_put(am_erts_internal, am_gather_microstate_accounting_result, 2);
     gather_system_check_res_trap
 	= erts_export_put(am_erts_internal, am_gather_system_check_result, 1);
+
+    is_process_alive_trap = erts_export_put(am_erts_internal, am_is_process_alive, 1);
+
+
     process_info_init();
     os_info_init();
 }
diff --git a/erts/emulator/beam/erl_message.c b/erts/emulator/beam/erl_message.c
index ed7a9d37c2..98feb95d99 100644
--- a/erts/emulator/beam/erl_message.c
+++ b/erts/emulator/beam/erl_message.c
@@ -323,7 +323,7 @@ erts_queue_dist_message(Process *rcvr,
              * TODO: We don't know the real size of the external message here.
              *       -1 will appear to a D script as 4294967295.
              */
-            DTRACE6(message_queued, receiver_name, -1, rcvr->msg.len + 1,
+            DTRACE6(message_queued, receiver_name, -1, rcvr->sig_qs.len + 1,
                     tok_label, tok_lastcnt, tok_serial);
         }
 #endif
diff --git a/erts/emulator/beam/erl_node_tables.c b/erts/emulator/beam/erl_node_tables.c
index ca83e70046..1f147011a8 100644
--- a/erts/emulator/beam/erl_node_tables.c
+++ b/erts/emulator/beam/erl_node_tables.c
@@ -1051,14 +1051,16 @@ static void erts_lcnt_enable_dist_lock_count(void *dep_raw, void *enable) {
     if(enable) {
         erts_lcnt_install_new_lock_info(&dep->rwmtx.lcnt, "dist_entry", dep->sysname, 
             ERTS_LOCK_TYPE_RWMUTEX | ERTS_LOCK_FLAGS_CATEGORY_DISTRIBUTION);
-        erts_lcnt_install_new_lock_info(&dep->lnk_mtx.lcnt, "dist_entry_links", dep->sysname,
-            ERTS_LOCK_TYPE_MUTEX | ERTS_LOCK_FLAGS_CATEGORY_DISTRIBUTION);
         erts_lcnt_install_new_lock_info(&dep->qlock.lcnt, "dist_entry_out_queue", dep->sysname,
             ERTS_LOCK_TYPE_MUTEX | ERTS_LOCK_FLAGS_CATEGORY_DISTRIBUTION);
+        if (dep->mld)
+            erts_lcnt_install_new_lock_info(&dep->mld->mtx.lcnt, "dist_entry_links", dep->sysname,
+                                            ERTS_LOCK_TYPE_MUTEX | ERTS_LOCK_FLAGS_CATEGORY_DISTRIBUTION);
     } else {
         erts_lcnt_uninstall(&dep->rwmtx.lcnt);
-        erts_lcnt_uninstall(&dep->lnk_mtx.lcnt);
         erts_lcnt_uninstall(&dep->qlock.lcnt);
+        if (dep->mld)
+            erts_lcnt_uninstall(&dep->mld->mtx.lcnt);
     }
 }
 
diff --git a/erts/emulator/beam/erl_proc_sig_queue.c b/erts/emulator/beam/erl_proc_sig_queue.c
index 1b5cbb1919..b4759967a7 100644
--- a/erts/emulator/beam/erl_proc_sig_queue.c
+++ b/erts/emulator/beam/erl_proc_sig_queue.c
@@ -48,7 +48,7 @@
  * Note that not all signal are handled using this functionality!
  */
 
-#define ERTS_SIG_Q_OP_MAX 9
+#define ERTS_SIG_Q_OP_MAX 10
 
 #define ERTS_SIG_Q_OP_EXIT                      0
 #define ERTS_SIG_Q_OP_EXIT_LINKED               1
@@ -59,7 +59,8 @@
 #define ERTS_SIG_Q_OP_UNLINK                    6
 #define ERTS_SIG_Q_OP_GROUP_LEADER              7
 #define ERTS_SIG_Q_OP_TRACE_CHANGE_STATE        8
-#define ERTS_SIG_Q_OP_PERSISTENT_MON_MSG        ERTS_SIG_Q_OP_MAX
+#define ERTS_SIG_Q_OP_PERSISTENT_MON_MSG        9
+#define ERTS_SIG_Q_OP_IS_ALIVE                  ERTS_SIG_Q_OP_MAX
 
 #define ERTS_SIG_Q_TYPE_MAX (ERTS_MON_LNK_TYPE_MAX + 5)
 
@@ -184,6 +185,11 @@ typedef struct {
     Eterm heap[1];
 } ErtsSigGroupLeader;
 
+typedef struct {
+    Eterm message;
+    Eterm requester;
+} ErtsIsAliveRequest;
+
 static int handle_msg_tracing(Process *c_p,
                               ErtsSigRecvTracing *tracing,
                               ErtsMessage ***next_nm_sig);
@@ -359,20 +365,47 @@ sig_enqueue_trace(Process *c_p, ErtsMessage *sig, int op,
 
 #ifdef USE_VM_PROBES
     case ERTS_SIG_Q_OP_EXIT:
-    case ERTS_SIG_Q_OP_EXIT_LINKED: {
-        ErtsExitSignalData *xsigd = get_exit_signal_data(sig);
-        if(DTRACE_ENABLED(process_exit_signal) && is_pid(xsigd->from)) {
-            DTRACE_CHARBUF(sender_str, DTRACE_TERM_BUF_SIZE);
-            DTRACE_CHARBUF(receiver_str, DTRACE_TERM_BUF_SIZE);
-            DTRACE_CHARBUF(reason_buf, DTRACE_TERM_BUF_SIZE);
+    case ERTS_SIG_Q_OP_EXIT_LINKED:
+
+        if (DTRACE_ENABLED(process_exit_signal)) {
+            Uint16 type = ERTS_PROC_SIG_TYPE(((ErtsSignal *) sig)->common.tag);
+            Eterm reason, from;
+
+            if (type == ERTS_SIG_Q_TYPE_GEN_EXIT) {
+                ErtsExitSignalData *xsigd = get_exit_signal_data(sig);
+                reason = xsigd->reason;
+                from = xsigd->from;
+            }
+            else {
+                ErtsLink *lnk = (ErtsLink *) sig, *olnk;
+
+                ASSERT(type == ERTS_LNK_TYPE_PROC
+                       || type == ERTS_LNK_TYPE_PORT
+                       || type == ERTS_LNK_TYPE_DIST_PROC);
+
+                olnk = erts_link_to_other(lnk, NULL);
+                reason = lnk->other.item;
+                from = olnk->other.item;
+            }
+
+            if (is_pid(from)) {
 
-            dtrace_pid_str(from, sender_str);
-            dtrace_proc_str(rp, receiver_str);
-            erts_snprintf(reason_buf, sizeof(DTRACE_CHARBUF_NAME(reason_buf)) - 1, "%T", reason);
-            DTRACE3(process_exit_signal, sender_str, receiver_str, reason_buf);
+                DTRACE_CHARBUF(sender_str, DTRACE_TERM_BUF_SIZE);
+                DTRACE_CHARBUF(receiver_str, DTRACE_TERM_BUF_SIZE);
+                DTRACE_CHARBUF(reason_buf, DTRACE_TERM_BUF_SIZE);
+
+                if (reason == am_kill) {
+                    reason = am_killed;
+                }
+
+                dtrace_pid_str(from, sender_str);
+                dtrace_proc_str(rp, receiver_str);
+                erts_snprintf(reason_buf, sizeof(DTRACE_CHARBUF_NAME(reason_buf)) - 1, "%T", reason);
+                DTRACE3(process_exit_signal, sender_str, receiver_str, reason_buf);
+            }
         }
         break;
-    }
+
 #endif
 
     default:
@@ -548,6 +581,43 @@ proc_queue_signal(Process *c_p, Eterm pid, ErtsSignal *sig, int op)
     return res;
 }
 
+static int
+maybe_elevate_sig_handling_prio(Process *c_p, Eterm other)
+{
+    /*
+     * returns:
+     *  > 0 -> elevated prio; process alive or exiting
+     *  < 0 -> no elevation needed; process alive or exiting
+     *    0 -> process terminated (free)
+     */
+    int res;
+    Process *rp;
+    erts_aint32_t state, my_prio, other_prio;
+
+    rp = erts_proc_lookup_raw(other);
+    if (!rp)
+        res = 0;
+    else {
+        res = -1;
+        state = erts_atomic32_read_nob(&c_p->state);
+        my_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
+
+        state = erts_atomic32_read_nob(&rp->state);
+        other_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
+
+        if (other_prio > my_prio) {
+            /* Others prio is lower than mine; elevate it... */
+            res = !!erts_sig_prio(other, my_prio);
+            if (res) {
+                /* ensure handled if dirty executing... */
+                state = erts_atomic32_read_nob(&rp->state);
+                ensure_dirty_proc_handled(other, state, my_prio);
+            }
+        }
+    }
+    return res;
+}
+
 void
 erts_proc_sig_fetch(Process *proc)
 {
@@ -765,7 +835,7 @@ send_gen_exit_signal(Process *c_p, Eterm from_tag,
     s_utag = (is_immed(utag)
               ? utag
               : copy_struct(utag, utag_sz, &hp, ohp));
-    ERL_MESSAGE_DT_UTAG(mp) = utag;
+    ERL_MESSAGE_DT_UTAG(mp) = s_utag;
 #endif
 
     ERL_MESSAGE_TERM(mp) = ERTS_PROC_SIG_MAKE_TAG(op,
@@ -1215,33 +1285,10 @@ erts_proc_sig_send_group_leader(Process *c_p, Eterm to, Eterm gl, Eterm ref)
     if (!res)
         destroy_sig_group_leader(sgl);
     else if (c_p) {
-        int prio_res = !0;
         erts_aint_t flags, rm_flags = ERTS_SIG_GL_FLG_SENDER;
-        Process *rp;
-        erts_aint32_t state, my_prio, other_prio;
-
-        state = erts_atomic32_read_nob(&c_p->state);
-        my_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
-
-        rp = erts_proc_lookup_raw(to);
-        if (!rp)
-            prio_res = 0;
-        else {
-            state = erts_atomic32_read_nob(&rp->state);
-            other_prio = ERTS_PSFLGS_GET_USR_PRIO(state);
-
-            if (other_prio > my_prio) {
-                /* Others prio is lower than mine; elevate it... */
-                prio_res = erts_sig_prio(to, my_prio);
-                if (prio_res) {
-                    state = erts_atomic32_read_nob(&rp->state);
-                    ensure_dirty_proc_handled(to, state, my_prio);
-                }
-            }
-        }
+        int prio_res = maybe_elevate_sig_handling_prio(c_p, to);
         if (!prio_res)
             rm_flags |= ERTS_SIG_GL_FLG_ACTIVE;
-
         flags = erts_atomic_read_band_nob(&sgl->flags, ~rm_flags);
         if (!prio_res && (flags & ERTS_SIG_GL_FLG_ACTIVE))
             res = 0; /* We deactivated signal... */
@@ -1253,6 +1300,99 @@ 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
+erts_proc_sig_send_is_alive_request(Process *c_p, Eterm to, Eterm ref)
+{
+    ErlHeapFragment *hfrag;
+    Uint hsz;
+    Eterm *hp, *start_hp, ref_cpy, msg;
+    ErlOffHeap *ohp;
+    ErtsMessage *mp;
+    ErtsIsAliveRequest *alive_req;
+
+    ASSERT(is_internal_ordinary_ref(ref));
+
+    hsz = ERTS_REF_THING_SIZE + 3 + sizeof(ErtsIsAliveRequest)/sizeof(Eterm);
+
+    mp = erts_alloc_message(hsz, &hp);
+    hfrag = &mp->hfrag;
+    mp->next = NULL;
+    ohp = &hfrag->off_heap;
+    start_hp = hp;
+
+    ref_cpy = STORE_NC(&hp, ohp, ref);
+    msg = TUPLE2(hp, ref_cpy, am_false); /* default res 'false' */
+    hp += 3;
+
+    hfrag->used_size = hp - start_hp;
+
+    alive_req = (ErtsIsAliveRequest *) (char *) hp;
+    alive_req->message = msg;
+    alive_req->requester = c_p->common.id;
+
+    ERL_MESSAGE_TERM(mp) = ERTS_PROC_SIG_MAKE_TAG(ERTS_SIG_Q_OP_IS_ALIVE,
+                                                  ERTS_SIG_Q_TYPE_UNDEFINED,
+                                                  0);
+    ERL_MESSAGE_TOKEN(mp) = NIL;
+    ERL_MESSAGE_FROM(mp) = am_system;
+#ifdef USE_VM_PROBES
+    ERL_MESSAGE_DT_UTAG(mp) = NIL;
+#endif
+
+    if (proc_queue_signal(c_p, to, (ErtsSignal *) mp, ERTS_SIG_Q_OP_IS_ALIVE))
+        (void) maybe_elevate_sig_handling_prio(c_p, to);
+    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);
+    }
+}
+
+static void
+is_alive_response(Process *c_p, ErtsMessage *mp, int is_alive)
+{
+    /*
+     * Sender prepared the message for us. Just patch
+     * the result if necessary. The default prepared
+     * result is 'false'.
+     */
+    Process *rp;
+    ErtsIsAliveRequest *alive_req;
+
+    alive_req = (ErtsIsAliveRequest *) (char *) (&mp->hfrag.mem[0]
+                                                 + mp->hfrag.used_size);
+
+
+    ASSERT(ERTS_SIG_IS_NON_MSG(mp));
+    ASSERT(ERTS_PROC_SIG_OP(((ErtsSignal *) mp)->common.tag)
+           == ERTS_SIG_Q_OP_IS_ALIVE);
+    ASSERT(mp->hfrag.alloc_size > mp->hfrag.used_size);
+    ASSERT((mp->hfrag.alloc_size - mp->hfrag.used_size)*sizeof(UWord)
+           >= sizeof(ErtsIsAliveRequest));
+    ASSERT(is_internal_pid(alive_req->requester));
+    ASSERT(alive_req->requester != c_p->common.id);
+    ASSERT(is_tuple_arity(alive_req->message, 2));
+    ASSERT(is_internal_ordinary_ref(tuple_val(alive_req->message)[1]));
+    ASSERT(tuple_val(alive_req->message)[2] == am_false);
+
+    ERL_MESSAGE_TERM(mp) = alive_req->message;
+    mp->data.attached = ERTS_MSG_COMBINED_HFRAG;
+    mp->next = NULL;
+
+    rp = erts_proc_lookup(alive_req->requester);
+    if (!rp)
+        erts_cleanup_messages(mp);
+    else {
+        if (is_alive) { /* patch result... */
+            Eterm *tp = tuple_val(alive_req->message);
+            tp[2] = am_true;
+        }
+        erts_queue_message(rp, 0, mp, alive_req->message, am_system);
+    }
+}
+
 static ERTS_INLINE void
 adjust_tracing_state(Process *c_p, ErtsSigRecvTracing *tracing, int setup)
 {
@@ -1447,8 +1587,8 @@ handle_exit_signal(Process *c_p, ErtsSigRecvTracing *tracing,
 {
     ErtsMessage *conv_msg = NULL;
     ErtsExitSignalData *xsigd = NULL;
-    ErtsLinkData *ldp;
-    ErtsLink *dlnk;
+    ErtsLinkData *ldp = NULL; /* Avoid erroneous warning... */
+    ErtsLink *dlnk = NULL; /* Avoid erroneous warning... */
     Eterm tag = ((ErtsSignal *) sig)->common.tag;
     Uint16 type = ERTS_PROC_SIG_TYPE(tag);
     int op = ERTS_PROC_SIG_OP(tag);
@@ -1472,8 +1612,6 @@ handle_exit_signal(Process *c_p, ErtsSigRecvTracing *tracing,
                 /* Link no longer active; ignore... */
                 ignore = !0;
                 destroy = !0;
-                ldp = NULL; /* Avoid erroneous warning... */
-                dlnk = NULL; /* Avoid erroneous warning... */
             }
             else {
                 ignore = 0;
@@ -2355,6 +2493,13 @@ erts_proc_sig_handle_incoming(Process *c_p, erts_aint32_t *statep,
             break;
         }
 
+        case ERTS_SIG_Q_OP_IS_ALIVE:
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            remove_nm_sig(c_p, sig, next_nm_sig);
+            is_alive_response(c_p, sig, !0);
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            break;
+
         case ERTS_SIG_Q_OP_TRACE_CHANGE_STATE: {
             Uint16 type = ERTS_PROC_SIG_TYPE(tag);
 
@@ -2667,6 +2812,12 @@ erts_proc_sig_handle_exit(Process *c_p, int *redsp)
             break;
         }
 
+        case ERTS_SIG_Q_OP_IS_ALIVE:
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            is_alive_response(c_p, sig, 0);
+            ERTS_PROC_SIG_HDBG_PRIV_CHKQ(c_p, &tracing, next_nm_sig);
+            break;
+
         case ERTS_SIG_Q_OP_TRACE_CHANGE_STATE:
             destroy_trace_info((ErtsSigTraceInfo *) sig);
             break;
@@ -2803,6 +2954,7 @@ erts_proc_sig_signal_size(ErtsSignal *sig)
         break;
 
     case ERTS_SIG_Q_OP_PERSISTENT_MON_MSG:
+    case ERTS_SIG_Q_OP_IS_ALIVE:
         size = ((ErtsMessage *) sig)->hfrag.alloc_size;
         size *= sizeof(Eterm);
         size += sizeof(ErtsMessage) - sizeof(Eterm);
@@ -3514,6 +3666,7 @@ erts_proc_sig_debug_foreach_sig(Process *c_p,
                     break;
                 }
 
+                case ERTS_SIG_Q_OP_IS_ALIVE:
                 case ERTS_SIG_Q_OP_TRACE_CHANGE_STATE:
                     break;
 
diff --git a/erts/emulator/beam/erl_proc_sig_queue.h b/erts/emulator/beam/erl_proc_sig_queue.h
index 433e30ce4a..56fe3e683e 100644
--- a/erts/emulator/beam/erl_proc_sig_queue.h
+++ b/erts/emulator/beam/erl_proc_sig_queue.h
@@ -31,6 +31,7 @@
  *              - Link
  *              - Unlink
  *              - Group leader
+ *              - Is process alive
  *              - Trace change
  *
  *              The signal queue consists of three parts:
@@ -426,6 +427,30 @@ void
 erts_proc_sig_send_group_leader(Process *c_p, Eterm to, Eterm gl,
                                 Eterm ref);
 
+/**
+ *
+ * @brief Send an 'is process alive' signal to a process.
+ *
+ * A response message '{Ref, Result}' is sent to the
+ * sender when performed where Ref is the reference passed
+ * as 'ref' argument, and Result is either 'true' or 'false'.
+ *
+ * @param[in]     c_p           Pointer to process struct of
+ *                              currently executing process.
+ *                              NULL if signal arrived via
+ *                              distribution.
+ *
+ * @param[in]     to            Identifier of receiver.
+ *
+ * @param[in]     ref           Reference to use in response
+ *                              message to the sending
+ *                              process (i.e., c_p).
+ *
+ */
+void
+erts_proc_sig_send_is_alive_request(Process *c_p, Eterm to,
+                                    Eterm ref);
+
 /*
  * End of send operations of currently supported process signals.
  */
diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 7969025f57..374583ec47 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -10501,6 +10501,8 @@ done:
     return st;
 }
 
+
+static void exit_permanent_prio_elevation(Process *c_p, erts_aint32_t state);
 static void save_gc_task(Process *c_p, ErtsProcSysTask *st, int prio);
 static void save_dirty_task(Process *c_p, ErtsProcSysTask *st);
 
@@ -10633,8 +10635,10 @@ execute_sys_tasks(Process *c_p, erts_aint32_t *statep, int in_reds)
                                                     reds, local_only);
             reds -= sig_reds;
 
-            if (state & ERTS_PSFLG_EXITING)
-                goto perm_elevate_prio;
+            if (state & ERTS_PSFLG_EXITING) {
+                exit_permanent_prio_elevation(c_p, state);
+                break;
+            }
 
             if (sig_res)
                 break;
@@ -10648,37 +10652,8 @@ execute_sys_tasks(Process *c_p, erts_aint32_t *statep, int in_reds)
                 st = NULL;
             }
             else {
-                erts_aint32_t a;
-
                 state = erts_atomic32_read_nob(&c_p->state);                         
-
-            perm_elevate_prio:
-
-                /*
-                 * we are about to terminate; permanently elevate
-                 * prio in order to ensure high prio signal
-                 * handling...
-                 */
-
-                a = state;
-                while (1) {
-                    erts_aint32_t aprio, uprio, n, e;
-                    ASSERT(!(a & ERTS_PSFLG_FREE));
-                    aprio = ERTS_PSFLGS_GET_ACT_PRIO(a);
-                    uprio = ERTS_PSFLGS_GET_USR_PRIO(a);
-                    if (aprio >= uprio)
-                        break; /* user prio >= actual prio */
-                    /*
-                     * actual prio is higher than user prio; raise
-                     * user prio to actual prio...
-                     */
-                    n = e = a;
-                    n &= ~ERTS_PSFLGS_USR_PRIO_MASK;
-                    n |= aprio << ERTS_PSFLGS_USR_PRIO_OFFSET;
-                    a = erts_atomic32_cmpxchg_mb(&c_p->state, n, e);
-                    if (a == e)
-                        break;
-                }
+                exit_permanent_prio_elevation(c_p, state);
             }
             break;
         }
@@ -10730,12 +10705,15 @@ cleanup_sys_tasks(Process *c_p, erts_aint32_t in_state, int in_reds)
 	}
 
 	switch (st->type) {
+        case ERTS_PSTT_PRIO_SIG:
+            state = erts_atomic32_read_nob(&c_p->state);                         
+            exit_permanent_prio_elevation(c_p, state);
+            /* fall through... */
         case ERTS_PSTT_GC_MAJOR:
         case ERTS_PSTT_GC_MINOR:
 	case ERTS_PSTT_CPC:
         case ERTS_PSTT_COHMQ:
         case ERTS_PSTT_ETS_FREE_FIXATION:
-        case ERTS_PSTT_PRIO_SIG:
 	    st_res = am_false;
 	    break;
 	case ERTS_PSTT_CLA:
@@ -10759,6 +10737,36 @@ cleanup_sys_tasks(Process *c_p, erts_aint32_t in_state, int in_reds)
     return reds;
 }
 
+static void
+exit_permanent_prio_elevation(Process *c_p, erts_aint32_t state)
+{
+    erts_aint32_t a;
+    /*
+     * we are about to terminate; permanently elevate
+     * prio in order to ensure high prio signal
+     * handling...
+     */
+    a = state;
+    while (1) {
+        erts_aint32_t aprio, uprio, n, e;
+        ASSERT(a & ERTS_PSFLG_EXITING);
+        ASSERT(!(a & ERTS_PSFLG_FREE));
+        aprio = ERTS_PSFLGS_GET_ACT_PRIO(a);
+        uprio = ERTS_PSFLGS_GET_USR_PRIO(a);
+        if (aprio >= uprio)
+            break; /* user prio >= actual prio */
+        /*
+         * actual prio is higher than user prio; raise
+         * user prio to actual prio...
+         */
+        n = e = a;
+        n &= ~ERTS_PSFLGS_USR_PRIO_MASK;
+        n |= aprio << ERTS_PSFLGS_USR_PRIO_OFFSET;
+        a = erts_atomic32_cmpxchg_mb(&c_p->state, n, e);
+        if (a == e)
+            break;
+    }
+}
 
 void
 erts_execute_dirty_system_task(Process *c_p)
@@ -12752,16 +12760,13 @@ erts_continue_exit_process(Process *p)
 
     erts_set_gc_state(p, 1);
     state = erts_atomic32_read_acqb(&p->state);
-    if ((state & ERTS_PSFLG_SYS_TASKS)
-        || p->dirty_sys_tasks
-        ) {
+    if ((state & ERTS_PSFLG_SYS_TASKS) || p->dirty_sys_tasks) {
 	if (cleanup_sys_tasks(p, state, CONTEXT_REDS) >= CONTEXT_REDS/2)
 	    goto yield;
     }
 
 #ifdef DEBUG
     erts_proc_lock(p, ERTS_PROC_LOCK_STATUS);
-    ASSERT(p->sys_task_qs == NULL);
     ASSERT(ERTS_PROC_GET_DELAYED_GC_TASK_QS(p) == NULL);
     ASSERT(p->dirty_sys_tasks == NULL);
     erts_proc_unlock(p, ERTS_PROC_LOCK_STATUS);
@@ -12873,7 +12878,30 @@ erts_continue_exit_process(Process *p)
            ? ERTS_PROC_SET_DIST_ENTRY(p, NULL)
            : NULL);
 
-    erts_proc_unlock(p, ERTS_PROC_LOCKS_ALL);
+
+    /*
+     * It might show up signal prio elevation tasks until we
+     * have entered free state. Cleanup such tasks now.
+     */
+    state = erts_atomic32_read_acqb(&p->state);
+    if (!(state & ERTS_PSFLG_SYS_TASKS))
+        erts_proc_unlock(p, ERTS_PROC_LOCKS_ALL);
+    else {
+        erts_proc_unlock(p, ERTS_PROC_LOCKS_ALL_MINOR);
+
+        do {
+            (void) cleanup_sys_tasks(p, state, CONTEXT_REDS);
+            state = erts_atomic32_read_acqb(&p->state);
+        } while (state & ERTS_PSFLG_SYS_TASKS);
+        
+        erts_proc_unlock(p, ERTS_PROC_LOCK_MAIN);
+    }
+
+#ifdef DEBUG
+    erts_proc_lock(p, ERTS_PROC_LOCK_STATUS);
+    ASSERT(p->sys_task_qs == NULL);
+    erts_proc_unlock(p, ERTS_PROC_LOCK_STATUS);
+#endif
 
     if (dep) {
         erts_do_net_exits(dep, (reason == am_kill) ? am_killed : reason);
diff --git a/erts/emulator/beam/io.c b/erts/emulator/beam/io.c
index b2afdc6bf2..9f87285b71 100644
--- a/erts/emulator/beam/io.c
+++ b/erts/emulator/beam/io.c
@@ -2361,6 +2361,21 @@ set_port_connected(int bang_op,
                 trace_port(prt, am_getting_linked, connect);
         }
 
+#ifdef USE_VM_PROBES
+	if (DTRACE_ENABLED(port_connect)) {
+            Eterm old_connected = ERTS_PORT_GET_CONNECTED(prt);
+            DTRACE_CHARBUF(process_str, DTRACE_TERM_BUF_SIZE);
+            DTRACE_CHARBUF(port_str, DTRACE_TERM_BUF_SIZE);
+            DTRACE_CHARBUF(newprocess_str, DTRACE_TERM_BUF_SIZE);
+
+            dtrace_pid_str(old_connected, process_str);
+            erts_snprintf(port_str, sizeof(DTRACE_CHARBUF_NAME(port_str)),
+                          "%T", prt->common.id);
+            dtrace_pid_str(connect, newprocess_str);
+            DTRACE4(port_connect, process_str, port_str, prt->name, newprocess_str);
+	}
+#endif
+
 	ERTS_PORT_SET_CONNECTED(prt, connect);
 
         if (IS_TRACED_FL(prt, F_TRACE_RECEIVE))
@@ -2370,18 +2385,6 @@ set_port_connected(int bang_op,
             trace_port_send(prt, from, TUPLE2(hp, prt->common.id, am_connected), 1);
         }
 
-#ifdef USE_VM_PROBES
-	if (DTRACE_ENABLED(port_connect)) {
-	    DTRACE_CHARBUF(process_str, DTRACE_TERM_BUF_SIZE);
-	    DTRACE_CHARBUF(port_str, DTRACE_TERM_BUF_SIZE);
-	    DTRACE_CHARBUF(newprocess_str, DTRACE_TERM_BUF_SIZE);
-
-	    dtrace_pid_str(connect, process_str);
-	    erts_snprintf(port_str, sizeof(DTRACE_CHARBUF_NAME(port_str)), "%T", prt->common.id);
-	    dtrace_proc_str(rp, newprocess_str);
-	    DTRACE4(port_connect, process_str, port_str, prt->name, newprocess_str);
-	}
-#endif
     }
 
     return ERTS_PORT_OP_DONE;
diff --git a/erts/emulator/beam/msg_instrs.tab b/erts/emulator/beam/msg_instrs.tab
index 88d2ef9fa3..6055e35717 100644
--- a/erts/emulator/beam/msg_instrs.tab
+++ b/erts/emulator/beam/msg_instrs.tab
@@ -235,7 +235,7 @@ remove_message() {
         }
         DTRACE6(message_receive,
                 receiver_name, size_object(ERL_MESSAGE_TERM(msgp)),
-                c_p->msg.len - 1, tok_label, tok_lastcnt, tok_serial);
+                c_p->sig_qs.len - 1, tok_label, tok_lastcnt, tok_serial);
     }
 #endif
     UNLINK_MESSAGE(c_p, msgp);
diff --git a/erts/emulator/test/bif_SUITE.erl b/erts/emulator/test/bif_SUITE.erl
index d16c6a320d..22706ae8b1 100644
--- a/erts/emulator/test/bif_SUITE.erl
+++ b/erts/emulator/test/bif_SUITE.erl
@@ -34,7 +34,8 @@
          erl_crash_dump_bytes/1,
 	 is_builtin/1, error_stacktrace/1,
 	 error_stacktrace_during_call_trace/1,
-         group_leader_prio/1, group_leader_prio_dirty/1]).
+         group_leader_prio/1, group_leader_prio_dirty/1,
+         is_process_alive/1]).
 
 suite() ->
     [{ct_hooks,[ts_install_cth]},
@@ -48,7 +49,8 @@ all() ->
      atom_to_binary, binary_to_atom, binary_to_existing_atom,
      erl_crash_dump_bytes, min_max, erlang_halt, is_builtin,
      error_stacktrace, error_stacktrace_during_call_trace,
-     group_leader_prio, group_leader_prio_dirty].
+     group_leader_prio, group_leader_prio_dirty,
+     is_process_alive].
 
 %% Uses erlang:display to test that erts_printf does not do deep recursion
 display(Config) when is_list(Config) ->
@@ -1076,6 +1078,27 @@ group_leader_prio_test(Dirty) ->
                   TLs),
     ok.
 
+is_process_alive(Config) when is_list(Config) ->
+    process_flag(priority, max),
+    Ps = lists:map(fun (_) ->
+                           spawn_opt(fun () -> tok_loop() end,
+                                     [{priority, high}, link])
+                   end,
+                   lists:seq(1, 2*erlang:system_info(schedulers))),
+    receive after 1000 -> ok end, %% Wait for load to spread
+    lists:foreach(fun (P) ->
+                          %% Ensure that signal order is preserved
+                          %% and that we are not starved due to
+                          %% priority inversion
+                          true = erlang:is_process_alive(P),
+                          unlink(P),
+                          true = erlang:is_process_alive(P),
+                          exit(P, kill),
+                          false = erlang:is_process_alive(P)
+                  end,
+                  Ps),
+    ok.
+
 %% helpers
     
 id(I) -> I.
diff --git a/erts/preloaded/ebin/erlang.beam b/erts/preloaded/ebin/erlang.beam
index 4d1691d71a..e93f053e01 100644
--- a/erts/preloaded/ebin/erlang.beam
+++ b/erts/preloaded/ebin/erlang.beam
diff --git a/erts/preloaded/ebin/erts_internal.beam b/erts/preloaded/ebin/erts_internal.beam
index 799c3e17fb..f5967780ad 100644
--- a/erts/preloaded/ebin/erts_internal.beam
+++ b/erts/preloaded/ebin/erts_internal.beam
diff --git a/erts/preloaded/src/erlang.erl b/erts/preloaded/src/erlang.erl
index f8221868e2..bffa59338e 100644
--- a/erts/preloaded/src/erlang.erl
+++ b/erts/preloaded/src/erlang.erl
@@ -39,7 +39,6 @@
 -export([integer_to_list/2]).
 -export([integer_to_binary/2]).
 -export([set_cpu_topology/1, format_cpu_topology/1]).
--export([await_proc_exit/3]).
 -export([memory/0, memory/1]).
 -export([alloc_info/1, alloc_sizes/1]).
 
@@ -3530,33 +3529,6 @@ rvrs(Xs) -> rvrs(Xs, []).
 rvrs([],Ys) -> Ys;
 rvrs([X|Xs],Ys) -> rvrs(Xs, [X|Ys]).
 
-%% erlang:await_proc_exit/3 is for internal use only!
-%%
-%% BIFs that need to await a specific process exit before
-%% returning traps to erlang:await_proc_exit/3.
-%%
-%% NOTE: This function is tightly coupled to
-%%       the implementation of the
-%%       erts_bif_prep_await_proc_exit_*()
-%%       functions in bif.c. Do not make
-%%       any changes to it without reading
-%%       the comment about them in bif.c!
--spec erlang:await_proc_exit(dst(), 'apply' | 'data' | 'reason', term()) -> term().
-await_proc_exit(Proc, Op, Data) ->
-    Mon = erlang:monitor(process, Proc),
-    receive
-	{'DOWN', Mon, process, _Proc, Reason} ->
-	    case Op of
-		apply ->
-		    {M, F, A} = Data,
-		    erlang:apply(M, F, A);
-		data ->
-		    Data;
-		reason ->
-		    Reason
-	    end
-    end.
-
 -spec min(Term1, Term2) -> Minimum when
       Term1 :: term(),
       Term2 :: term(),
diff --git a/erts/preloaded/src/erts_internal.erl b/erts/preloaded/src/erts_internal.erl
index fb709e7482..da5c9c68ed 100644
--- a/erts/preloaded/src/erts_internal.erl
+++ b/erts/preloaded/src/erts_internal.erl
@@ -78,6 +78,8 @@
 %% Auto import name clash
 -export([check_process_code/1]).
 
+-export([is_process_alive/1, is_process_alive/2]).
+
 %%
 %% Await result of send to port
 %%
@@ -600,3 +602,22 @@ group_leader(_GL, _Pid) ->
 
 group_leader(_GL, _Pid, _Ref) ->
     erlang:nif_error(undefined).
+
+-spec erts_internal:is_process_alive(Pid, Ref) -> 'ok' when
+      Pid :: pid(),
+      Ref :: reference().
+
+is_process_alive(_Pid, _Ref) ->
+    erlang:nif_error(undefined).    
+
+-spec erts_internal:is_process_alive(Pid) -> boolean() when
+      Pid :: pid().
+
+is_process_alive(Pid) ->
+    Ref = make_ref(),
+    erts_internal:is_process_alive(Pid, Ref),
+    receive
+        {Ref, Res} ->
+            Res
+    end.
+