1 files changed, 168 insertions, 31 deletions

diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index b24f26138c..99a4011b8f 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -967,11 +967,25 @@ typedef struct {
     erts_smp_atomic32_t refc;
 } ErtsSchedWallTimeReq;
 
+typedef struct {
+    Process *proc;
+    Eterm ref;
+    Eterm ref_heap[REF_THING_SIZE];
+    Uint req_sched;
+    erts_smp_atomic32_t refc;
+} ErtsSystemCheckReq;
+
+
 #if !HALFWORD_HEAP
 ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(swtreq,
 				 ErtsSchedWallTimeReq,
 				 5,
 				 ERTS_ALC_T_SCHED_WTIME_REQ)
+
+ERTS_SCHED_PREF_QUICK_ALLOC_IMPL(screq,
+				 ErtsSystemCheckReq,
+				 5,
+				 ERTS_ALC_T_SYS_CHECK_REQ)
 #else
 static ERTS_INLINE ErtsSchedWallTimeReq *
 swtreq_alloc(void)
@@ -985,6 +999,19 @@ swtreq_free(ErtsSchedWallTimeReq *ptr)
 {
     erts_free(ERTS_ALC_T_SCHED_WTIME_REQ, ptr);
 }
+
+static ERTS_INLINE ErtsSystemCheckReq *
+screq_alloc(void)
+{
+    return erts_alloc(ERTS_ALC_T_SYS_CHECK_REQ,
+		      sizeof(ErtsSystemCheckReq));
+}
+
+static ERTS_INLINE void
+screq_free(ErtsSystemCheckReq *ptr)
+{
+    erts_free(ERTS_ALC_T_SYS_CHECK_REQ, ptr);
+}
 #endif
 
 static void
@@ -1118,6 +1145,75 @@ erts_sched_wall_time_request(Process *c_p, int set, int enable)
     return ref;
 }
 
+static void
+reply_system_check(void *vscrp)
+{
+    ErtsSchedulerData *esdp = erts_get_scheduler_data();
+    ErtsSystemCheckReq *scrp = (ErtsSystemCheckReq *) vscrp;
+    ErtsProcLocks rp_locks = (scrp->req_sched == esdp->no ? ERTS_PROC_LOCK_MAIN : 0);
+    Process *rp = scrp->proc;
+    Eterm msg;
+    Eterm *hp = NULL;
+    Eterm **hpp;
+    Uint sz;
+    ErlOffHeap *ohp = NULL;
+    ErlHeapFragment *bp = NULL;
+
+    ASSERT(esdp);
+#ifdef ERTS_DIRTY_SCHEDULERS
+    ASSERT(!ERTS_SCHEDULER_IS_DIRTY(esdp));
+#endif
+
+    sz = REF_THING_SIZE;
+    hp = erts_alloc_message_heap(sz, &bp, &ohp, rp, &rp_locks);
+    hpp = &hp;
+    msg = STORE_NC(hpp, ohp, scrp->ref);
+
+    erts_queue_message(rp, &rp_locks, bp, msg, NIL);
+
+    if (scrp->req_sched == esdp->no)
+	rp_locks &= ~ERTS_PROC_LOCK_MAIN;
+
+    if (rp_locks)
+	erts_smp_proc_unlock(rp, rp_locks);
+
+    erts_proc_dec_refc(rp);
+
+    if (erts_smp_atomic32_dec_read_nob(&scrp->refc) == 0)
+	screq_free(vscrp);
+}
+
+
+Eterm erts_system_check_request(Process *c_p) {
+    ErtsSchedulerData *esdp = ERTS_PROC_GET_SCHDATA(c_p);
+    Eterm ref;
+    ErtsSystemCheckReq *scrp;
+    Eterm *hp;
+
+    scrp = screq_alloc();
+    ref = erts_make_ref(c_p);
+    hp = &scrp->ref_heap[0];
+
+    scrp->proc = c_p;
+    scrp->ref = STORE_NC(&hp, NULL, ref);
+    scrp->req_sched = esdp->no;
+    erts_smp_atomic32_init_nob(&scrp->refc, (erts_aint32_t) erts_no_schedulers);
+
+    erts_proc_add_refc(c_p, (Sint) erts_no_schedulers);
+
+#ifdef ERTS_SMP
+    if (erts_no_schedulers > 1)
+	erts_schedule_multi_misc_aux_work(1,
+					  erts_no_schedulers,
+					  reply_system_check,
+					  (void *) scrp);
+#endif
+
+    reply_system_check((void *) scrp);
+
+    return ref;
+}
+
 static ERTS_INLINE ErtsProcList *
 proclist_create(Process *p)
 {
@@ -5792,6 +5888,7 @@ erts_init_scheduling(int no_schedulers, int no_schedulers_online
     init_misc_aux_work();
 #if !HALFWORD_HEAP
     init_swtreq_alloc();
+    init_screq_alloc();
 #endif
 
     erts_atomic32_init_nob(&debug_wait_completed_count, 0); /* debug only */
@@ -6462,9 +6559,6 @@ suspend_process(Process *c_p, Process *p)
 
     if (suspended) {
 
-	ASSERT(!(ERTS_PSFLG_RUNNING & state)
-	       || p == erts_get_current_process());
-
 	if (suspended > 0 && erts_system_profile_flags.runnable_procs) {
 
 	    /* 'state' is before our change... */
@@ -8411,9 +8505,8 @@ pid2proc_not_running(Process *c_p, ErtsProcLocks c_p_locks,
 	    resume_process(rp, rp_locks);
     }
     else {
-
 	rp = erts_pid2proc(c_p, c_p_locks|ERTS_PROC_LOCK_STATUS,
-			   pid, pid_locks|ERTS_PROC_LOCK_STATUS);
+			   pid, ERTS_PROC_LOCK_STATUS);
 
 	if (!rp) {
 	    c_p->flags &= ~F_P2PNR_RESCHED;
@@ -8422,40 +8515,84 @@ pid2proc_not_running(Process *c_p, ErtsProcLocks c_p_locks,
 
 	ASSERT(!(c_p->flags & F_P2PNR_RESCHED));
 
-	if (suspend) {
-	    if (suspend_process(c_p, rp))
-		goto done;
-	}
-	else {
-	    if (!((ERTS_PSFLG_RUNNING|ERTS_PSFLG_RUNNING_SYS)
-		  & erts_smp_atomic32_read_acqb(&rp->state)))
-		goto done;
+	/*
+	 * Suspend the other process in order to prevent
+	 * it from being selected for normal execution.
+	 * This will however not prevent it from being
+	 * selected for execution of a system task. If
+	 * it is selected for execution of a system task
+	 * we might be blocked for quite a while if the
+	 * try-lock below fails. That is, there is room
+	 * for improvement here...
+	 */
 
-	}
+	if (!suspend_process(c_p, rp)) {
+	    /* Other process running */
 
-	/* Other process running */
+	    ASSERT(ERTS_PSFLG_RUNNING
+		   & erts_smp_atomic32_read_nob(&rp->state));
 
-	/*
-	 * If we got pending suspenders and suspend ourselves waiting
-	 * to suspend another process we might deadlock.
-	 * In this case we have to yield, be suspended by
-	 * someone else and then do it all over again.
-	 */
-	if (!c_p->pending_suspenders) {
-	    /* Mark rp pending for suspend by c_p */
-	    add_pend_suspend(rp, c_p->common.id, handle_pend_sync_suspend);
-	    ASSERT(is_nil(c_p->suspendee));
+	running:
 
-	    /* Suspend c_p; when rp is suspended c_p will be resumed. */
-	    suspend_process(c_p, c_p);
-	    c_p->flags |= F_P2PNR_RESCHED;
+	    /*
+	     * If we got pending suspenders and suspend ourselves waiting
+	     * to suspend another process we might deadlock.
+	     * In this case we have to yield, be suspended by
+	     * someone else and then do it all over again.
+	     */
+	    if (!c_p->pending_suspenders) {
+		/* Mark rp pending for suspend by c_p */
+		add_pend_suspend(rp, c_p->common.id, handle_pend_sync_suspend);
+		ASSERT(is_nil(c_p->suspendee));
+
+		/* Suspend c_p; when rp is suspended c_p will be resumed. */
+		suspend_process(c_p, c_p);
+		c_p->flags |= F_P2PNR_RESCHED;
+	    }
+	    /* Yield (caller is assumed to yield immediately in bif). */
+	    erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_STATUS);
+	    rp = ERTS_PROC_LOCK_BUSY;
+	}
+	else {
+	    ErtsProcLocks need_locks = pid_locks & ~ERTS_PROC_LOCK_STATUS;
+	    if (need_locks && erts_smp_proc_trylock(rp, need_locks) == EBUSY) {
+		if (ERTS_PSFLG_RUNNING_SYS
+		    & erts_smp_atomic32_read_nob(&rp->state)) {
+		    /* Executing system task... */
+		    resume_process(rp, ERTS_PROC_LOCK_STATUS);
+		    goto running;
+		}
+		erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_STATUS);
+		/*
+		 * If we are unlucky, the process just got selected for
+		 * execution of a system task. In this case we may be
+		 * blocked here for quite a while... Execution of system
+		 * tasks are fortunately quite rare events. We try to
+		 * avoid this by checking if it is in a state executing
+		 * system tasks (above), but it will not prevent all
+		 * scenarios for a long block here...
+		 */
+		rp = erts_pid2proc(c_p, c_p_locks|ERTS_PROC_LOCK_STATUS,
+				   pid, pid_locks|ERTS_PROC_LOCK_STATUS);
+		if (!rp)
+		    goto done;
+	    }
+
+	    /*
+	     * The previous suspend has prevented the process
+	     * from being selected for normal execution regardless
+	     * of locks held or not held on it...
+	     */
+	    ASSERT(!(ERTS_PSFLG_RUNNING
+		     & erts_smp_atomic32_read_nob(&rp->state)));
+
+	    if (!suspend)
+		resume_process(rp, pid_locks|ERTS_PROC_LOCK_STATUS);
 	}
-	/* Yield (caller is assumed to yield immediately in bif). */
-	erts_smp_proc_unlock(rp, pid_locks|ERTS_PROC_LOCK_STATUS);
-	rp = ERTS_PROC_LOCK_BUSY;
     }
 
  done:
+	
     if (rp && rp != ERTS_PROC_LOCK_BUSY && !(pid_locks & ERTS_PROC_LOCK_STATUS))
 	erts_smp_proc_unlock(rp, ERTS_PROC_LOCK_STATUS);
     if (unlock_c_p_status)