X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=urcu-qsbr.c;h=c678d38779eb683f1f78872a87e853a4c281f43d;hb=935b11ff4cf9053954d21b9d63c4ee367b12a652;hp=155505abc7843385fafef29de57509ceb096519c;hpb=2dfb8b5e30bc2d268bcbc57eceb9c54d21b36d90;p=urcu.git

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 155505a..c678d38 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -113,13 +113,24 @@ static void update_counter_and_wait(void)
 	struct rcu_reader *index, *tmp;
 
 #if (BITS_PER_LONG < 64)
-	/* Switch parity: 1 -> 0, 0 -> 1 */
+	/* Switch parity: 0 -> 1, 1 -> 0 */
 	STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
 #else	/* !(BITS_PER_LONG < 64) */
 	/* Increment current G.P. */
 	STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
 #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.
+	 *
+	 * 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.
 	 */