X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=src%2Furcu-defer-impl.h;h=0c8339997d0501d3719344e965bd2d7c74e34ff7;hb=993937267e0781190eeff042438fd6d3c15d5cf3;hp=969231f8b552aa733dc5aedd91c8fd86ece5981c;hpb=70469b43316ecc8d6053550504858ad8a8ef9b16;p=userspace-rcu.git

diff --git a/src/urcu-defer-impl.h b/src/urcu-defer-impl.h
index 969231f..0c83399 100644
--- a/src/urcu-defer-impl.h
+++ b/src/urcu-defer-impl.h
@@ -194,17 +194,25 @@ static void wait_defer(void)
 		uatomic_set(&defer_thread_futex, 0);
 	} else {
 		cmm_smp_rmb();	/* Read queue before read futex */
-		if (uatomic_read(&defer_thread_futex) != -1)
-			return;
-		while (futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
-				NULL, NULL, 0)) {
+		while (uatomic_read(&defer_thread_futex) == -1) {
+			if (!futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
+				/*
+				 * Prior queued wakeups queued by unrelated code
+				 * using the same address can cause futex wait to
+				 * return 0 even through the futex value is still
+				 * -1 (spurious wakeups). Check the value again
+				 * in user-space to validate whether it really
+				 * differs from -1.
+				 */
+				continue;
+			}
 			switch (errno) {
-			case EWOULDBLOCK:
+			case EAGAIN:
 				/* Value already changed. */
 				return;
 			case EINTR:
 				/* Retry if interrupted by signal. */
-				break;	/* Get out of switch. */
+				break;	/* Get out of switch. Check again. */
 			default:
 				/* Unexpected error. */
 				urcu_die(errno);
@@ -265,8 +273,6 @@ void rcu_defer_barrier_thread(void)
 	_rcu_defer_barrier_thread();
 	mutex_unlock(&rcu_defer_mutex);
 }
-URCU_ATTR_ALIAS(urcu_stringify(rcu_defer_barrier_thread))
-void alias_rcu_defer_barrier_thread();
 
 /*
  * rcu_defer_barrier - Execute all queued rcu callbacks.
@@ -307,8 +313,6 @@ void rcu_defer_barrier(void)
 end:
 	mutex_unlock(&rcu_defer_mutex);
 }
-URCU_ATTR_ALIAS(urcu_stringify(rcu_defer_barrier))
-void alias_rcu_defer_barrier();
 
 /*
  * _defer_rcu - Queue a RCU callback.
@@ -401,7 +405,6 @@ void defer_rcu(void (*fct)(void *p), void *p)
 {
 	_defer_rcu(fct, p);
 }
-URCU_ATTR_ALIAS(urcu_stringify(defer_rcu)) void alias_defer_rcu();
 
 static void start_defer_thread(void)
 {
@@ -450,8 +453,6 @@ int rcu_defer_register_thread(void)
 	mutex_unlock(&defer_thread_mutex);
 	return 0;
 }
-URCU_ATTR_ALIAS(urcu_stringify(rcu_defer_register_thread))
-int alias_rcu_defer_register_thread();
 
 void rcu_defer_unregister_thread(void)
 {
@@ -470,14 +471,10 @@ void rcu_defer_unregister_thread(void)
 		stop_defer_thread();
 	mutex_unlock(&defer_thread_mutex);
 }
-URCU_ATTR_ALIAS(urcu_stringify(rcu_defer_unregister_thread))
-void alias_rcu_defer_unregister_thread();
 
 void rcu_defer_exit(void)
 {
 	assert(cds_list_empty(&registry_defer));
 }
-URCU_ATTR_ALIAS(urcu_stringify(rcu_defer_exit))
-void alias_rcu_defer_exit();
 
 #endif /* _URCU_DEFER_IMPL_H */