RCU: update barrier comments

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/src/rcu.h b/src/rcu.h
index e9f0fe6a8da5829e40a68f35a15a106a4a836f34..61a6fb0cc72ac5ba7daba2c81f9bf537b897b5a7 100644 (file)
--- a/src/rcu.h
+++ b/src/rcu.h
@@ -165,6 +165,13 @@ void side_rcu_wait_grace_period(struct side_rcu_gp_state *gp_state)
        /*
         * This memory barrier (D) pairs with memory barriers (A) and
         * (B) on the read-side.
+        *
+        * It orders prior loads and stores before the "end"/"begin"
+        * reader state loads. In other words, it orders prior loads and
+        * stores before observation of active readers quiescence,
+        * effectively ensuring that read-side critical sections which
+        * exist after the grace period completes are ordered after
+        * loads and stores performed before the grace period.
         */
        __atomic_thread_fence(__ATOMIC_SEQ_CST);
 
@@ -198,6 +205,14 @@ end:
        /*
         * This memory barrier (E) pairs with memory barriers (A) and
         * (B) on the read-side.
+        *
+        * It orders the "end"/"begin" reader state loads before
+        * following loads and stores. In other words, it orders
+        * observation of active readers quiescence before following
+        * loads and stores, effectively ensuring that read-side
+        * critical sections which existed prior to the grace period
+        * are ordered before loads and stores performed after the grace
+        * period.
         */
        __atomic_thread_fence(__ATOMIC_SEQ_CST);
 }