X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;f=src%2Furcu-defer-impl.h;h=f1fae9c0d15ce4364a44d511f2a4701febe0c4b5;hb=070e8aeccb9f9dbfed57245e78839eb181c66db5;hp=b34a1a17b11adabd9cc8da0aca6d030106889755;hpb=ce28e67a534dcf0b68ccad2218e5a2e552e6e469;p=userspace-rcu.git

diff --git a/src/urcu-defer-impl.h b/src/urcu-defer-impl.h
index b34a1a1..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);
@@ -376,7 +384,7 @@ static void _defer_rcu(void (*fct)(void *p), void *p)
 	wake_up_defer();
 }
 
-static void *thr_defer(void *args)
+static void *thr_defer(void *args __attribute__((unused)))
 {
 	for (;;) {
 		/*