X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=src%2Fcommon%2Ffutex.cpp;h=e178b7e1b4f1e8a99de25e42b10733266353ada0;hb=36962e16797b5ca590c54a385ca594e2859ef8c2;hp=3eadf096bc8086760e36b24f3a342341d048c9fa;hpb=21cf9b6b1843774306a76f4dccddddd706b64f79;p=lttng-tools.git

diff --git a/src/common/futex.cpp b/src/common/futex.cpp
index 3eadf096b..e178b7e1b 100644
--- a/src/common/futex.cpp
+++ b/src/common/futex.cpp
@@ -12,9 +12,9 @@
 #include <urcu.h>
 #include <urcu/futex.h>
 
-#include <common/common.h>
+#include <common/common.hpp>
 
-#include "futex.h"
+#include "futex.hpp"
 
 /*
  * This futex wait/wake scheme only works for N wakers / 1 waiters. Hence the
@@ -72,16 +72,25 @@ void futex_nto1_wait(int32_t *futex)
 {
 	cmm_smp_mb();
 
-	if (uatomic_read(futex) != -1)
-		goto end;
-	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. */
 			goto end;
 		case EINTR:
 			/* Retry if interrupted by signal. */
-			break;	/* Get out of switch. */
+			break;	/* Get out of switch. Check again. */
 		default:
 			/* Unexpected error. */
 			PERROR("futex_async");