X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=src%2Furcu-defer-impl.h;h=f1fae9c0d15ce4364a44d511f2a4701febe0c4b5;hb=feb9779741e503a39fadc838d1b26984bfd51f7e;hp=969231f8b552aa733dc5aedd91c8fd86ece5981c;hpb=d60603e846c6d14893b57f627b1b66d751550486;p=urcu.git

diff --git a/src/urcu-defer-impl.h b/src/urcu-defer-impl.h
index 969231f..f1fae9c 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);