X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=9542b264a6dbf53d36d2fb63e7578b4e7ff2b2f5;hp=ac1a4d6c9314499d339fdd2a939479ec96deed5f;hb=9598a4814c854780e9ca9bb2cfff8d77442c3db6;hpb=bb48818526ec4317f9e6daeb0aa1cd64d528f754

diff --git a/urcu.c b/urcu.c
index ac1a4d6..9542b26 100644
--- a/urcu.c
+++ b/urcu.c
@@ -125,41 +125,70 @@ 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();
+
+	internal_urcu_lock();
+	debug_yield_write();
+
+	switch_next_urcu_qparity();	/* 0 -> 1 */
 	debug_yield_write();
 
 	/*
-	 * Wait for previous parity to be empty of readers.
+	 * 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).
 	 */
-	wait_for_quiescent_state();
-}
+	mb();
 
-void synchronize_rcu(void)
-{
-	debug_yield_write();
-	internal_urcu_lock();
+	/*
+	 * Wait for previous parity to be empty of readers.
+	 */
+	wait_for_quiescent_state();	/* Wait readers in parity 0 */
 	debug_yield_write();
-	switch_qparity();
+
+	/*
+	 * 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).
+	 */
+	mb();
+
+	switch_next_urcu_qparity();	/* 1 -> 0 */
 	debug_yield_write();
-	switch_qparity();
+
+	/*
+	 * 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).
+	 */
+	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)