X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;ds=sidebyside;f=src%2Furcu-qsbr.c;h=e5ac0539c47072154084bdb518b8a559076b1e55;hb=0c8eff157de6f7ab836ec87a340a517d49fdaca3;hp=3709412f2519ff7259da6bb144f9818584842580;hpb=e37faee15dd9f26c131e064f4e3afe357afe1c73;p=userspace-rcu.git

diff --git a/src/urcu-qsbr.c b/src/urcu-qsbr.c
index 3709412..e5ac053 100644
--- a/src/urcu-qsbr.c
+++ b/src/urcu-qsbr.c
@@ -53,6 +53,7 @@
 #define _LGPL_SOURCE
 
 void __attribute__((destructor)) urcu_qsbr_exit(void);
+static void urcu_call_rcu_exit(void);
 
 /*
  * rcu_gp_lock ensures mutual exclusion between threads calling
@@ -125,17 +126,25 @@ static void wait_gp(void)
 {
 	/* Read reader_gp before read futex */
 	cmm_smp_rmb();
-	if (uatomic_read(&urcu_qsbr_gp.futex) != -1)
-		return;
-	while (futex_noasync(&urcu_qsbr_gp.futex, FUTEX_WAIT, -1,
-			NULL, NULL, 0)) {
+	while (uatomic_read(&urcu_qsbr_gp.futex) == -1) {
+		if (!futex_noasync(&urcu_qsbr_gp.futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
+			/*
+			 * Prior queued wakeups queued by unrelated code
+			 * using the same address can cause futex wait to
+			 * return 0 even through the futex value is still
+			 * -1 (spurious wakeups). Check the value again
+			 * in user-space to validate whether it really
+			 * differs from -1.
+			 */
+			continue;
+		}
 		switch (errno) {
-		case EWOULDBLOCK:
+		case EAGAIN:
 			/* Value already changed. */
 			return;
 		case EINTR:
 			/* Retry if interrupted by signal. */
-			break;	/* Get out of switch. */
+			break;	/* Get out of switch. Check again. */
 		default:
 			/* Unexpected error. */
 			urcu_die(errno);
@@ -516,6 +525,7 @@ void urcu_qsbr_exit(void)
 	 * readers, and left running at exit.
 	 * assert(cds_list_empty(&registry));
 	 */
+	urcu_call_rcu_exit();
 }
 URCU_ATTR_ALIAS("urcu_qsbr_exit") void rcu_exit_qsbr();