nova: don't wait for workers in cpu_session::pause

If a local thread is attempted to be 'pause'd via cpu_session, don't wait
until it gets into the recalled state. If the caller is lucky it is, if not
return only the stack pointer.

Avoids deadlocking of the gdb when attached to a process running a server.

Issue #478

base-nova/include/base/pager.h

@@ -135,6 +135,7 @@ namespace Genode {
 			/**
 			 * Set initial stack pointer used by the startup handler
 			 */
+			addr_t initial_esp() { return _initial_esp; }
 			void initial_esp(addr_t esp) { _initial_esp = esp; }
 
 			/**
@@ -183,14 +184,14 @@ namespace Genode {
 			/**
 			 * Copy thread state of recalled thread.
 			 */
-			int copy_thread_state(Thread_state * state_dst)
+			bool copy_thread_state(Thread_state * state_dst)
 			{
 				if (!state_dst || !_state.is_valid())
-					return -1;
+					return false;
 
 				*state_dst = _state.thread;
 
-				return 0;
+				return true;
 			}
 
 			/**

base-nova/src/core/include/platform_thread.h

@@ -37,13 +37,24 @@ namespace Genode {
 			addr_t             _id_base;
 			addr_t             _sel_exc_base;
 			Affinity::Location _location;
-			bool               _is_main_thread;
-			bool               _is_vcpu;
+
+			enum {
+				MAIN_THREAD = 0x1U,
+				VCPU        = 0x2U,
+				WORKER      = 0x4U,
+			};
+			uint8_t            _features;
+
 			char               _name[Thread_base::Context::NAME_LEN];
 
 			addr_t _sel_ec() const { return _id_base; }
 			addr_t _sel_sc() const { return _id_base + 1; }
 
+			/* convenience function to access _feature variable */
+			inline bool is_main_thread() { return _features & MAIN_THREAD; }
+			inline bool is_vcpu()        { return _features & VCPU; }
+			inline bool is_worker()      { return _features & WORKER; }
+
 		public:
 
 			/* invalid thread number */
@@ -144,9 +155,11 @@ namespace Genode {
 			/**
 			 * Associate thread with protection domain
 			 */
-			void bind_to_pd(Platform_pd *pd, bool is_main_thread)
+			void bind_to_pd(Platform_pd *pd, bool main_thread)
 			{
-				_pd = pd, _is_main_thread = is_main_thread;
+				_pd = pd;
+
+				if (main_thread) _features |= MAIN_THREAD;
 			}
 
 			void single_step(bool on);

base-nova/src/core/platform_thread.cc

@@ -63,9 +63,9 @@ int Platform_thread::start(void *ip, void *sp)
 		return -2;
 	}
 
-	if (!_is_main_thread) {
+	if (!is_main_thread()) {
 		addr_t initial_sp = reinterpret_cast<addr_t>(sp);
-		addr_t utcb       = _is_vcpu ? 0 : round_page(initial_sp);
+		addr_t utcb       = is_vcpu() ? 0 : round_page(initial_sp);
 
 		if (_sel_exc_base == Native_thread::INVALID_INDEX) {
 			PERR("exception base not specified");
@@ -82,6 +82,13 @@ int Platform_thread::start(void *ip, void *sp)
 			return -4;
 		}
 
+		if (!thread_global) {
+			_features |= WORKER;
+
+			/* local/worker threads do not require a startup portal */
+			revoke(Obj_crd(_pager->exc_pt_sel_client() + PT_SEL_STARTUP, 0));
+		}
+
 		_pager->initial_eip((addr_t)ip);
 		_pager->initial_esp(initial_sp);
 		_pager->client_set_ec(_sel_ec());
@@ -181,18 +188,20 @@ int Platform_thread::start(void *ip, void *sp)
 
 Native_capability Platform_thread::pause()
 {
-	if (!_pager)
-		return Native_capability::invalid_cap();
+	if (!_pager) return Native_capability();
 
 	Native_capability notify_sm = _pager->notify_sm();
 	if (!notify_sm.valid()) return notify_sm;
 
- 	if (_pager->client_recall() != Nova::NOVA_OK)
-		return Native_capability::invalid_cap();
+	if (_pager->client_recall() != Nova::NOVA_OK)
+		return Native_capability();
 
-	/* If the thread is blocked in the its own SM, get him out */
+	/* If the thread is blocked in its own SM, get him out */
 	cancel_blocking();
 
+	/* local thread may never get be canceled if it doesn't receive an IPC */
+	if (is_worker()) return Native_capability();
+
 	return notify_sm;
 }
 
@@ -201,8 +210,10 @@ void Platform_thread::resume()
 {
 	using namespace Nova;
 
-	uint8_t res = create_sc(_sel_sc(), _pd->pd_sel(), _sel_ec(), Qpd());
-	if (res == NOVA_OK) return;
+	if (!is_worker()) {
+		uint8_t res = create_sc(_sel_sc(), _pd->pd_sel(), _sel_ec(), Qpd());
+		if (res == NOVA_OK) return;
+	}
 
 	if (!_pager) return;
 
@@ -213,9 +224,15 @@ void Platform_thread::resume()
 
 Thread_state Platform_thread::state()
 {
-	Thread_state s;
 	if (!_pager) throw Cpu_session::State_access_failed();
-	_pager->copy_thread_state(&s);
+
+	Thread_state s;
+	if (_pager->copy_thread_state(&s))
+		return s;
+
+	if (is_worker())
+		s.sp = _pager->initial_esp();
+
 	return s;
 }
 
@@ -223,20 +240,20 @@ Thread_state Platform_thread::state()
 void Platform_thread::state(Thread_state s)
 {
 	/* not permitted for main thread */
-	if (_is_main_thread) throw Cpu_session::State_access_failed();
+	if (is_main_thread()) throw Cpu_session::State_access_failed();
 
 	/* you can do it only once */
 	if (_sel_exc_base != Native_thread::INVALID_INDEX)
 		throw Cpu_session::State_access_failed();
 
 	/*
-	 * _sel_exc_base  exception base of thread in caller
+	 * s.sel_exc_base exception base of thread in caller
 	 *                protection domain - not in Core !
-	 * _is_vcpu       If true it will run as vCPU,
-	 *                 otherwise it will be a thread.
+	 * s.is_vcpu      If true it will run as vCPU,
+	 *                otherwise it will be a thread.
 	 */
 	_sel_exc_base = s.sel_exc_base;
-	_is_vcpu      = s.is_vcpu;
+	if (s.is_vcpu) _features |= VCPU;
 }
 
 
@@ -272,7 +289,7 @@ Platform_thread::Platform_thread(const char *name, unsigned, int thread_id)
 :
 	_pd(0), _pager(0), _id_base(cap_selector_allocator()->alloc(1)),
 	_sel_exc_base(Native_thread::INVALID_INDEX), _location(boot_cpu(), 0),
-	_is_main_thread(false), _is_vcpu(false)
+	_features(0)
 {
 	strncpy(_name, name, sizeof(_name));
 }