X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=src%2Furcu-wait.h;h=93e8e516d868e7bba5b481416d3095b3154fc3fb;hb=65eaf4b646f566324b92c25c8760a204bfbdffa8;hp=c586ec9da8a007519cc7d6a793a9b6598cea46be;hpb=014775106c60f02818ca755b331f887030bd440f;p=urcu.git

diff --git a/src/urcu-wait.h b/src/urcu-wait.h
index c586ec9..93e8e51 100644
--- a/src/urcu-wait.h
+++ b/src/urcu-wait.h
@@ -26,6 +26,7 @@
 #include <urcu/assert.h>
 #include <urcu/uatomic.h>
 #include <urcu/wfstack.h>
+#include <urcu/futex.h>
 #include "urcu-die.h"
 
 /*
@@ -154,15 +155,26 @@ void urcu_adaptative_busy_wait(struct urcu_wait_node *wait)
 			goto skip_futex_wait;
 		caa_cpu_relax();
 	}
-	while (futex_noasync(&wait->state, FUTEX_WAIT, URCU_WAIT_WAITING,
-			NULL, NULL, 0)) {
+	while (uatomic_read(&wait->state) == URCU_WAIT_WAITING) {
+		if (!futex_noasync(&wait->state, FUTEX_WAIT, URCU_WAIT_WAITING, 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
+			 * URCU_WAIT_WAITING (spurious wakeups). Check
+			 * the value again in user-space to validate
+			 * whether it really differs from
+			 * URCU_WAIT_WAITING.
+			 */
+			continue;
+		}
 		switch (errno) {
-		case EWOULDBLOCK:
+		case EAGAIN:
 			/* Value already changed. */
 			goto skip_futex_wait;
 		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);