X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=urcu.c;h=0e42207e2bcd59d82127dc308def83b85c424798;hb=40e140c9f237bbe8c50d4a5355561139f01afb70;hp=9542b264a6dbf53d36d2fb63e7578b4e7ff2b2f5;hpb=9598a4814c854780e9ca9bb2cfff8d77442c3db6;p=urcu.git

diff --git a/urcu.c b/urcu.c
index 9542b26..0e42207 100644
--- a/urcu.c
+++ b/urcu.c
@@ -43,7 +43,9 @@ unsigned int __thread rand_yield;
 
 static struct reader_data *reader_data;
 static int num_readers, alloc_readers;
+#ifndef DEBUG_FULL_MB
 static int sig_done;
+#endif
 
 void internal_urcu_lock(void)
 {
@@ -75,38 +77,52 @@ static void switch_next_urcu_qparity(void)
 }
 
 #ifdef DEBUG_FULL_MB
+static void force_mb_single_thread(pthread_t tid)
+{
+	smp_mb();
+}
+
 static void force_mb_all_threads(void)
 {
-	mb();
+	smp_mb();
 }
 #else
+
+static void force_mb_single_thread(pthread_t tid)
+{
+	assert(reader_data);
+	sig_done = 0;
+	smp_mb();	/* write sig_done before sending the signals */
+	pthread_kill(tid, SIGURCU);
+	/*
+	 * Wait for sighandler (and thus mb()) to execute on every thread.
+	 * BUSY-LOOP.
+	 */
+	while (sig_done < 1)
+		smp_rmb();	/* ensure we re-read sig-done */
+	smp_mb();	/* read sig_done before ending the barrier */
+}
+
 static void force_mb_all_threads(void)
 {
 	struct reader_data *index;
 	/*
-	 * Ask for each threads to execute a mb() so we can consider the
+	 * Ask for each threads to execute a smp_mb() so we can consider the
 	 * compiler barriers around rcu read lock as real memory barriers.
 	 */
 	if (!reader_data)
 		return;
-	debug_yield_write();
 	sig_done = 0;
-	debug_yield_write();
-	mb();	/* write sig_done before sending the signals */
-	debug_yield_write();
-	for (index = reader_data; index < reader_data + num_readers; index++) {
+	smp_mb();	/* write sig_done before sending the signals */
+	for (index = reader_data; index < reader_data + num_readers; index++)
 		pthread_kill(index->tid, SIGURCU);
-		debug_yield_write();
-	}
 	/*
 	 * Wait for sighandler (and thus mb()) to execute on every thread.
 	 * BUSY-LOOP.
 	 */
 	while (sig_done < num_readers)
-		barrier();
-	debug_yield_write();
-	mb();	/* read sig_done before ending the barrier */
-	debug_yield_write();
+		smp_rmb();	/* ensure we re-read sig-done */
+	smp_mb();	/* read sig_done before ending the barrier */
 }
 #endif
 
@@ -116,14 +132,21 @@ void wait_for_quiescent_state(void)
 
 	if (!reader_data)
 		return;
-	/* Wait for each thread urcu_active_readers count to become 0.
+	/*
+	 * Wait for each thread urcu_active_readers count to become 0.
 	 */
 	for (index = reader_data; index < reader_data + num_readers; index++) {
+		int wait_loops = 0;
 		/*
-		 * BUSY-LOOP.
+		 * BUSY-LOOP. Force the reader thread to commit its
+		 * urcu_active_readers update to memory if we wait for too long.
 		 */
-		while (rcu_old_gp_ongoing(index->urcu_active_readers))
-			barrier();
+		while (rcu_old_gp_ongoing(index->urcu_active_readers)) {
+			if (wait_loops++ == KICK_READER_LOOPS) {
+				force_mb_single_thread(index->tid);
+				wait_loops = 0;
+			}
+		}
 	}
 }
 
@@ -133,13 +156,10 @@ void synchronize_rcu(void)
 	 * where new ptr points to. */
 	/* Write new ptr before changing the qparity */
 	force_mb_all_threads();
-	debug_yield_write();
 
 	internal_urcu_lock();
-	debug_yield_write();
 
 	switch_next_urcu_qparity();	/* 0 -> 1 */
-	debug_yield_write();
 
 	/*
 	 * Must commit qparity update to memory before waiting for parity
@@ -147,13 +167,12 @@ void synchronize_rcu(void)
 	 * waiting forever while new readers are always accessing data (no
 	 * progress).
 	 */
-	mb();
+	smp_mb();
 
 	/*
 	 * Wait for previous parity to be empty of readers.
 	 */
 	wait_for_quiescent_state();	/* Wait readers in parity 0 */
-	debug_yield_write();
 
 	/*
 	 * Must finish waiting for quiescent state for parity 0 before
@@ -161,10 +180,9 @@ void synchronize_rcu(void)
 	 * the writer waiting forever while new readers are always accessing
 	 * data (no progress).
 	 */
-	mb();
+	smp_mb();
 
 	switch_next_urcu_qparity();	/* 1 -> 0 */
-	debug_yield_write();
 
 	/*
 	 * Must commit qparity update to memory before waiting for parity
@@ -172,23 +190,20 @@ void synchronize_rcu(void)
 	 * waiting forever while new readers are always accessing data (no
 	 * progress).
 	 */
-	mb();
+	smp_mb();
 
 	/*
 	 * Wait for previous parity to be empty of readers.
 	 */
 	wait_for_quiescent_state();	/* Wait readers in parity 1 */
-	debug_yield_write();
 
 	internal_urcu_unlock();
-	debug_yield_write();
 
 	/* All threads should finish using the data referred to by old ptr
 	 * before decrementing their urcu_active_readers count */
 	/* Finish waiting for reader threads before letting the old ptr being
 	 * freed. */
 	force_mb_all_threads();
-	debug_yield_write();
 }
 
 void urcu_add_reader(pthread_t id)
@@ -256,7 +271,12 @@ void urcu_unregister_thread(void)
 #ifndef DEBUG_FULL_MB
 void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
-	mb();
+	/*
+	 * Executing this smp_mb() is the only purpose of this signal handler.
+	 * It punctually promotes barrier() into smp_mb() on every thread it is
+	 * executed on.
+	 */
+	smp_mb();
 	atomic_inc(&sig_done);
 }