X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=src%2Fcommon%2Ffutex.c;h=80bdb01fb6f9e834c2d27564562edc34ce51e8e4;hb=717918b72e07062b62f96baaf1ae480b0a929617;hp=332289924ab9ac3e1d88e54df78417175afa7238;hpb=ab5be9fa2eb5ba9600a82cd18fd3cfcbac69169a;p=lttng-tools.git

diff --git a/src/common/futex.c b/src/common/futex.c
index 332289924..80bdb01fb 100644
--- a/src/common/futex.c
+++ b/src/common/futex.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2011 David Goulet <david.goulet@polymtl.ca>
+ * Copyright (C) 2011 EfficiOS Inc.
  * Copyright (C) 2011 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  *
  * SPDX-License-Identifier: GPL-2.0-only
@@ -75,16 +75,25 @@ 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");