X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=src%2Fworkqueue.c;h=283a37132b88245734aed2631704b15bae99c3e4;hb=80a665a638813723582e8c2c4a0ccb919f1a3e04;hp=cadcf874be6c76726dc1a3dd3e082c545b266e8b;hpb=9cd319f7a2e479bec7c694740f9c7bba8f6d2876;p=userspace-rcu.git

diff --git a/src/workqueue.c b/src/workqueue.c
index cadcf87..283a371 100644
--- a/src/workqueue.c
+++ b/src/workqueue.c
@@ -129,18 +129,29 @@ static int set_thread_cpu_affinity(struct urcu_workqueue *workqueue __attribute_
 
 static void futex_wait(int32_t *futex)
 {
+	int ret;
+
 	/* Read condition before read futex */
 	cmm_smp_mb();
-	if (uatomic_read(futex) != -1)
-		return;
-	while (futex_async(futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
+	while (uatomic_read(futex) == -1) {
+		if (!futex_async(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);