X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=urcu-qsbr.c;h=b043b8592e7f04f1606bd3b734b2130e09c260e9;hb=d40fde2c4f6170c3ace770354d99acc9e9732ec5;hp=25074d09063a60ae5c94a17b18cd9d241b1e2fb9;hpb=7a5a38f52b8814d0188b74a91cb635bc205df96c;p=urcu.git

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 25074d0..b043b85 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -121,12 +121,20 @@ static void update_counter_and_wait(void)
 #endif	/* !(BITS_PER_LONG < 64) */
 
 	/*
-	 * Enforce compiler-order of store to rcu_gp_ctr before before
-	 * load rcu_reader ctr.
-	 * This ensures synchronize_rcu() cannot be starved by readers.
+	 * Must commit rcu_gp_ctr update to memory before waiting for quiescent
+	 * state. Failure to do so could result in the writer waiting forever
+	 * while new readers are always accessing data (no progress). Enforce
+	 * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
 	 */
 	barrier();
 
+	/*
+	 * Adding a smp_mb() which is _not_ formally required, but makes the
+	 * model easier to understand. It does not have a big performance impact
+	 * anyway, given this is the write-side.
+	 */
+	smp_mb();
+
 	/*
 	 * Wait for each thread rcu_reader_qs_gp count to become 0.
 	 */
@@ -204,11 +212,12 @@ void synchronize_rcu(void)
 
 	/*
 	 * 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).
-	 * Ensured by STORE_SHARED and LOAD_SHARED.
+	 * committing next rcu_gp_ctr update to memory. Failure to do so could
+	 * result in the writer waiting forever while new readers are always
+	 * accessing data (no progress).  Enforce compiler-order of load
+	 * rcu_reader ctr before store to rcu_gp_ctr.
 	 */
+	barrier();
 
 	/*
 	 * Adding a smp_mb() which is _not_ formally required, but makes the