diff --git a/src/system/kernel/UserEvent.cpp b/src/system/kernel/UserEvent.cpp
index 7d890d9cf5..fb8c0b9725 100644
--- a/src/system/kernel/UserEvent.cpp
+++ b/src/system/kernel/UserEvent.cpp
@@ -31,22 +31,20 @@ struct SignalEvent::EventSignal : Signal {
 	{
 	}
 
-	bool IsInUse() const
+	bool MarkUsed()
 	{
-		return fInUse;
+		return atomic_set(reinterpret_cast<vint32*>(&fInUse), true);
 	}
 
-	void SetInUse(bool inUse)
+	void SetUnused()
 	{
-		fInUse = inUse;
+		fInUse = false;
 	}
 
 	virtual void Handled()
 	{
 		// mark not-in-use
-		InterruptsSpinLocker schedulerLocker(gSchedulerLock);
 		fInUse = false;
-		schedulerLocker.Unlock();
 
 		Signal::Handled();
 	}
@@ -111,20 +109,22 @@ TeamSignalEvent::Create(Team* team, uint32 signalNumber, int32 signalCode,
 status_t
 TeamSignalEvent::Fire()
 {
-	// called with the scheduler lock held
-	if (fSignal->IsInUse())
+	if (fSignal->MarkUsed())
 		return B_BUSY;
 
 	fSignal->AcquireReference();
 		// one reference is transferred to send_signal_to_team_locked
+
+	InterruptsSpinLocker locker(gSchedulerLock);
 	status_t error = send_signal_to_team_locked(fTeam, fSignal->Number(),
 		fSignal, B_DO_NOT_RESCHEDULE);
 	if (error == B_OK) {
-		// Mark the signal in-use. There are situations (for certain signals),
-		// in which send_signal_to_team_locked() succeeds without queuing the
-		// signal.
-		fSignal->SetInUse(fSignal->IsPending());
+		// There are situations (for certain signals), in which
+		// send_signal_to_team_locked() succeeds without queuing the signal.
+		if (!fSignal->IsPending())
+			fSignal->SetUnused();
 	}
+	locker.Unlock();
 
 	return error;
 }
@@ -165,20 +165,22 @@ ThreadSignalEvent::Create(Thread* thread, uint32 signalNumber, int32 signalCode,
 status_t
 ThreadSignalEvent::Fire()
 {
-	// called with the scheduler lock held
-	if (fSignal->IsInUse())
+	if (fSignal->MarkUsed())
 		return B_BUSY;
 
 	fSignal->AcquireReference();
 		// one reference is transferred to send_signal_to_team_locked
+
+	InterruptsSpinLocker locker(gSchedulerLock);
 	status_t error = send_signal_to_thread_locked(fThread, fSignal->Number(),
 		fSignal, B_DO_NOT_RESCHEDULE);
 	if (error == B_OK) {
-		// Mark the signal in-use. There are situations (for certain signals),
-		// in which send_signal_to_team_locked() succeeds without queuing the
-		// signal.
-		fSignal->SetInUse(fSignal->IsPending());
+		// There are situations (for certain signals), in which
+		// send_signal_to_team_locked() succeeds without queuing the signal.
+		if (!fSignal->IsPending())
+			fSignal->SetUnused();
 	}
+	locker.Unlock();
 
 	return error;
 }
@@ -216,12 +218,11 @@ CreateThreadEvent::Create(const ThreadCreationAttributes& attributes)
 status_t
 CreateThreadEvent::Fire()
 {
-	if (fPendingDPC)
+	bool wasPending = atomic_set(reinterpret_cast<vint32*>(&fPendingDPC), true);
+	if (wasPending)
 		return B_BUSY;
 
-	fPendingDPC = true;
-
-	DPCQueue::DefaultQueue(B_NORMAL_PRIORITY)->Add(this, true);
+	DPCQueue::DefaultQueue(B_NORMAL_PRIORITY)->Add(this);
 
 	return B_OK;
 }
@@ -231,10 +232,7 @@ void
 CreateThreadEvent::DoDPC(DPCQueue* queue)
 {
 	// We're no longer queued in the DPC queue, so we can be reused.
-	{
-		InterruptsSpinLocker schedulerLocker(gSchedulerLock);
-		fPendingDPC = false;
-	}
+	fPendingDPC = false;
 
 	// create the thread
 	thread_id threadID = thread_create_thread(fCreationAttributes, false);