base: release signal context from signal list

Remove signal context object from signal source component list (_signal_queue)
before destruction, otherwise we get a dangling pointer.

On native hardware for base-nova, the signal source thread triggered page
faults in the Signal_source_component::wait_for_signal() method when the signal
context got freed up in Signal_session_component::free_context but was still
enqueued in Signal_source_component::_signal_queue.

Fixes #600

base-foc/src/core/signal_source_component.cc

@@ -32,6 +32,12 @@ using namespace Genode;
  ** Signal-source component **
  *****************************/
 
+void Signal_source_component::release(Signal_context_component *context)
+{
+	if (context && context->is_enqueued())
+		_signal_queue.remove(context);
+}
+
 void Signal_source_component::submit(Signal_context_component *context,
                                      Ipc_ostream              *ostream,
                                      int                       cnt)

base-nova/src/core/signal_source_component.cc

@@ -30,6 +30,12 @@ using namespace Genode;
  ** Signal-source component **
  *****************************/
 
+void Signal_source_component::release(Signal_context_component *context)
+{
+	if (context && context->is_enqueued())
+		_signal_queue.remove(context);
+}
+
 void Signal_source_component::submit(Signal_context_component *context,
                                      Ipc_ostream              *ostream,
                                      int                       cnt)
@@ -41,8 +47,7 @@ void Signal_source_component::submit(Signal_context_component *context,
 		_signal_queue.enqueue(context);
 
 		/* wake up client */
-		Nova::sm_ctrl(_blocking_semaphore.local_name(),
+		Nova::sm_ctrl(_blocking_semaphore.local_name(), Nova::SEMAPHORE_UP);
-		              Nova::SEMAPHORE_UP);
 	}
 }
 
@@ -67,8 +72,7 @@ Signal_source_component::Signal_source_component(Rpc_entrypoint *ep)
 {
 	/* initialized blocking semaphore */
 	addr_t sem_sel = cap_selector_allocator()->alloc();
-	uint8_t ret = Nova::create_sm(sem_sel,
+	uint8_t ret = Nova::create_sm(sem_sel, Platform_pd::pd_core_sel(), 0);
-	                              Platform_pd::pd_core_sel(), 0);
 	if (ret)
 		PERR("create_sm returned %u", ret);
 

base/src/core/include/signal_session_component.h

@@ -48,6 +48,11 @@ namespace Genode {
 			Signal_context_component(long imprint, Signal_source_component *source)
 			: _imprint(imprint), _cnt(0), _source(source) { }
 
+			/**
+			 * De-constructor
+			 */
+			~Signal_context_component(); 
+
 			/**
 			 * Increment number of signals to be delivered at once
 			 */
@@ -79,6 +84,8 @@ namespace Genode {
 			 */
 			Signal_source_component(Rpc_entrypoint *rpc_entrypoint);
 
+			void release(Signal_context_component *context);
+
 			void submit(Signal_context_component *context,
 			            Ipc_ostream              *ostream,
 			            int                       cnt);

base/src/core/signal_session_component.cc

@@ -40,12 +40,13 @@ Signal_session_component::Signal_session_component(Rpc_entrypoint *source_ep,
 
 Signal_session_component::~Signal_session_component()
 {
+	/* remove _signal_source from entrypoint */
+	_source_ep->dissolve(&_source);
+
 	/* free all signal contexts */
 	while (Signal_context_component *r = _contexts_slab.first_object())
 		free_context(r->cap());
 
-	/* remove _signal_source from entrypoint */
-	_source_ep->dissolve(&_source);
 }
 
 
@@ -99,3 +100,8 @@ void Signal_session_component::submit(Signal_context_capability context_cap,
 
 	context->source()->submit(context, _ipc_ostream, cnt);
 }
+
+Signal_context_component::~Signal_context_component() {
+	if (is_enqueued() && _source)
+		_source->release(this);
+}

base/src/core/signal_source_component.cc

@@ -25,6 +25,12 @@ using namespace Genode;
  ** Signal-source component **
  *****************************/
 
+void Signal_source_component::release(Signal_context_component *context)
+{
+	if (context && context->is_enqueued())
+		_signal_queue.remove(context);
+}
+
 void Signal_source_component::submit(Signal_context_component *context,
                                      Ipc_ostream              *ostream,
                                      int                       cnt)