X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=urcu-qsbr.c;h=8d8a9cf05ced0fd18ef9943110dc22a2e6e05e87;hb=2d47d69ea0876148b5628aa8f7bd9f030a8c5d2f;hp=87cf41d7ee70f274dc6676af06e3c122dd986222;hpb=6d841bc23fc94345fe76651d73c1a3f821a85aa7;p=urcu.git

diff --git a/urcu-qsbr.c b/urcu-qsbr.c
index 87cf41d..8d8a9cf 100644
--- a/urcu-qsbr.c
+++ b/urcu-qsbr.c
@@ -52,6 +52,11 @@ int32_t gp_futex;
  */
 unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
 
+/*
+ * Active attempts to check for reader Q.S. before calling futex().
+ */
+#define RCU_QS_ACTIVE_ATTEMPTS 100
+
 /*
  * Written to only by each individual reader. Read by both the reader and the
  * writers.
@@ -145,26 +150,33 @@ static void update_counter_and_wait(void)
 	 */
 	for (;;) {
 		wait_loops++;
-		if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
-			uatomic_dec(&gp_futex);
+		if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
+			uatomic_set(&gp_futex, -1);
+			/*
+			 * Write futex before write waiting (the other side
+			 * reads them in the opposite order).
+			 */
+			cmm_smp_wmb();
+			cds_list_for_each_entry(index, &registry, node) {
+				_CMM_STORE_SHARED(index->waiting, 1);
+			}
 			/* Write futex before read reader_gp */
 			cmm_smp_mb();
 		}
-
 		cds_list_for_each_entry_safe(index, tmp, &registry, node) {
 			if (!rcu_gp_ongoing(&index->ctr))
 				cds_list_move(&index->node, &qsreaders);
 		}
 
 		if (cds_list_empty(&registry)) {
-			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 				/* Read reader_gp before write futex */
 				cmm_smp_mb();
 				uatomic_set(&gp_futex, 0);
 			}
 			break;
 		} else {
-			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
+			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 				wait_gp();
 			} else {
 #ifndef HAS_INCOHERENT_CACHES