X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=src%2Furcu-defer-impl.h;fp=src%2Furcu-defer-impl.h;h=b5d79262c03bb88a28cd376d78c4189ca3c578cd;hp=d25e9b93f4dc17e8f1e6ee986ad04cdca366527f;hb=879a3e166178d16b2ffedc73899904d52285cfe8;hpb=98d705dd32be11b3f134b5aed87f9c201c028c10

diff --git a/src/urcu-defer-impl.h b/src/urcu-defer-impl.h
index d25e9b9..b5d7926 100644
--- a/src/urcu-defer-impl.h
+++ b/src/urcu-defer-impl.h
@@ -194,17 +194,25 @@ static void wait_defer(void)
 		uatomic_set(&defer_thread_futex, 0);
 	} else {
 		cmm_smp_rmb();	/* Read queue before read futex */
-		if (uatomic_read(&defer_thread_futex) != -1)
-			return;
-		while (futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
-				NULL, NULL, 0)) {
+		while (uatomic_read(&defer_thread_futex) == -1) {
+			if (!futex_noasync(&defer_thread_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);