X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=urcu-qsbr.c;h=52cb04aee9ff1b1b5a7b2caef45d6d5b5317ba77;hb=11eb040f24e020d05d65983d0f87f79b000c7b9f;hp=ec483d925c0bdbfc85e8a0dfeb1690849a940705;hpb=1745be1a65fcf0398247b03ed30efeeeba52482a;p=urcu.git

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index ec483d9..52cb04a 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -51,7 +51,21 @@
 
 void __attribute__((destructor)) rcu_exit(void);
 
+/*
+ * rcu_gp_lock ensures mutual exclusion between threads calling
+ * synchronize_rcu().
+ */
 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
+/*
+ * rcu_registry_lock ensures mutual exclusion between threads
+ * registering and unregistering themselves to/from the registry, and
+ * with threads reading that registry from synchronize_rcu(). However,
+ * this lock is not held all the way through the completion of awaiting
+ * for the grace period. It is sporadically released between iterations
+ * on the registry.
+ * rcu_registry_lock may nest inside rcu_gp_lock.
+ */
+static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 
 int32_t gp_futex;
 
@@ -111,15 +125,32 @@ static void wait_gp(void)
 {
 	/* Read reader_gp before read futex */
 	cmm_smp_rmb();
-	if (uatomic_read(&gp_futex) == -1)
-		futex_noasync(&gp_futex, FUTEX_WAIT, -1,
-		      NULL, NULL, 0);
+	if (uatomic_read(&gp_futex) != -1)
+		return;
+	while (futex_noasync(&gp_futex, FUTEX_WAIT, -1,
+			NULL, NULL, 0)) {
+		switch (errno) {
+		case EWOULDBLOCK:
+			/* Value already changed. */
+			return;
+		case EINTR:
+			/* Retry if interrupted by signal. */
+			break;	/* Get out of switch. */
+		default:
+			/* Unexpected error. */
+			urcu_die(errno);
+		}
+	}
 }
 
+/*
+ * Always called with rcu_registry lock held. Releases this lock between
+ * iterations and grabs it again. Holds the lock when it returns.
+ */
 static void update_counter_and_wait(void)
 {
 	CDS_LIST_HEAD(qsreaders);
-	int wait_loops = 0;
+	unsigned int wait_loops = 0;
 	struct rcu_reader *index, *tmp;
 
 #if (CAA_BITS_PER_LONG < 64)
@@ -150,7 +181,8 @@ static void update_counter_and_wait(void)
 	 * Wait for each thread rcu_reader_qs_gp count to become 0.
 	 */
 	for (;;) {
-		wait_loops++;
+		if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
+			wait_loops++;
 		if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 			uatomic_set(&gp_futex, -1);
 			/*
@@ -177,6 +209,8 @@ static void update_counter_and_wait(void)
 			}
 			break;
 		} else {
+			/* Temporarily unlock the registry lock. */
+			mutex_unlock(&rcu_registry_lock);
 			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 				wait_gp();
 			} else {
@@ -186,6 +220,8 @@ static void update_counter_and_wait(void)
 				cmm_smp_mb();
 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 			}
+			/* Re-lock the registry lock before the next loop. */
+			mutex_lock(&rcu_registry_lock);
 		}
 	}
 	/* put back the reader list in the registry */
@@ -218,12 +254,15 @@ void synchronize_rcu(void)
 		cmm_smp_mb();
 
 	mutex_lock(&rcu_gp_lock);
+	mutex_lock(&rcu_registry_lock);
 
 	if (cds_list_empty(&registry))
 		goto out;
 
 	/*
 	 * Wait for previous parity to be empty of readers.
+	 * update_counter_and_wait() can release and grab again
+	 * rcu_registry_lock interally.
 	 */
 	update_counter_and_wait();	/* 0 -> 1, wait readers in parity 0 */
 
@@ -246,9 +285,12 @@ void synchronize_rcu(void)
 
 	/*
 	 * Wait for previous parity to be empty of readers.
+	 * update_counter_and_wait() can release and grab again
+	 * rcu_registry_lock interally.
 	 */
 	update_counter_and_wait();	/* 1 -> 0, wait readers in parity 1 */
 out:
+	mutex_unlock(&rcu_registry_lock);
 	mutex_unlock(&rcu_gp_lock);
 
 	/*
@@ -278,10 +320,16 @@ void synchronize_rcu(void)
 		cmm_smp_mb();
 
 	mutex_lock(&rcu_gp_lock);
+	mutex_lock(&rcu_registry_lock);
 	if (cds_list_empty(&registry))
 		goto out;
+	/*
+	 * update_counter_and_wait() can release and grab again
+	 * rcu_registry_lock interally.
+	 */
 	update_counter_and_wait();
 out:
+	mutex_unlock(&rcu_registry_lock);
 	mutex_unlock(&rcu_gp_lock);
 
 	if (was_online)
@@ -325,9 +373,9 @@ void rcu_register_thread(void)
 	URCU_TLS(rcu_reader).tid = pthread_self();
 	assert(URCU_TLS(rcu_reader).ctr == 0);
 
-	mutex_lock(&rcu_gp_lock);
+	mutex_lock(&rcu_registry_lock);
 	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
-	mutex_unlock(&rcu_gp_lock);
+	mutex_unlock(&rcu_registry_lock);
 	_rcu_thread_online();
 }
 
@@ -338,9 +386,9 @@ void rcu_unregister_thread(void)
 	 * with a waiting writer.
 	 */
 	_rcu_thread_offline();
-	mutex_lock(&rcu_gp_lock);
+	mutex_lock(&rcu_registry_lock);
 	cds_list_del(&URCU_TLS(rcu_reader).node);
-	mutex_unlock(&rcu_gp_lock);
+	mutex_unlock(&rcu_registry_lock);
 }
 
 void rcu_exit(void)