X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=018e09b8601b041621fc6f72afdaeb57839e895c;hp=ac1a4d6c9314499d339fdd2a939479ec96deed5f;hb=ae878d0dcc291dba7c5722eed13294195a64409e;hpb=bb48818526ec4317f9e6daeb0aa1cd64d528f754

diff --git a/urcu.c b/urcu.c
index ac1a4d6..018e09b 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)
 {
@@ -77,36 +79,29 @@ static void switch_next_urcu_qparity(void)
 #ifdef DEBUG_FULL_MB
 static void force_mb_all_threads(void)
 {
-	mb();
+	smp_mb();
 }
 #else
 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_mb();	/* read sig_done before ending the barrier */
 }
 #endif
 
@@ -125,41 +120,62 @@ void wait_for_quiescent_state(void)
 		while (rcu_old_gp_ongoing(index->urcu_active_readers))
 			barrier();
 	}
-	/*
-	 * Locally : read *index->urcu_active_readers before freeing old
-	 * pointer.
-	 * Remote (reader threads) : Order urcu_qparity update and other
-	 * thread's quiescent state counter read.
-	 */
-	force_mb_all_threads();
 }
 
-static void switch_qparity(void)
+void synchronize_rcu(void)
 {
-	/* All threads should read qparity before accessing data structure. */
-	/* Write ptr before changing the qparity */
+	/* All threads should read qparity before accessing data structure
+	 * where new ptr points to. */
+	/* Write new ptr before changing the qparity */
 	force_mb_all_threads();
-	debug_yield_write();
-	switch_next_urcu_qparity();
-	debug_yield_write();
+
+	internal_urcu_lock();
+
+	switch_next_urcu_qparity();	/* 0 -> 1 */
+
+	/*
+	 * Must commit qparity update to memory before waiting for parity
+	 * 0 quiescent state. Failure to do so could result in the writer
+	 * waiting forever while new readers are always accessing data (no
+	 * progress).
+	 */
+	smp_mb();
 
 	/*
 	 * Wait for previous parity to be empty of readers.
 	 */
-	wait_for_quiescent_state();
-}
+	wait_for_quiescent_state();	/* Wait readers in parity 0 */
+
+	/*
+	 * Must finish waiting for quiescent state for parity 0 before
+	 * committing qparity update to memory. Failure to do so could result in
+	 * the writer waiting forever while new readers are always accessing
+	 * data (no progress).
+	 */
+	smp_mb();
+
+	switch_next_urcu_qparity();	/* 1 -> 0 */
+
+	/*
+	 * Must commit qparity update to memory before waiting for parity
+	 * 1 quiescent state. Failure to do so could result in the writer
+	 * waiting forever while new readers are always accessing data (no
+	 * progress).
+	 */
+	smp_mb();
+
+	/*
+	 * Wait for previous parity to be empty of readers.
+	 */
+	wait_for_quiescent_state();	/* Wait readers in parity 1 */
 
-void synchronize_rcu(void)
-{
-	debug_yield_write();
-	internal_urcu_lock();
-	debug_yield_write();
-	switch_qparity();
-	debug_yield_write();
-	switch_qparity();
-	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();
 }
 
 void urcu_add_reader(pthread_t id)
@@ -227,7 +243,7 @@ void urcu_unregister_thread(void)
 #ifndef DEBUG_FULL_MB
 void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
-	mb();
+	smp_mb();
 	atomic_inc(&sig_done);
 }