X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=src%2Furcu-qsbr.c;fp=src%2Furcu-qsbr.c;h=a3382857a7f358ab2f6bd548df6504c35e8bbadf;hp=d69d93b1018e2740a0bf9f6fec877a012820f1e8;hb=4974ad5f21d2cb17d313504f8d1252738526d588;hpb=a18d0428065b301086d4e8a85bc057dc39946891

diff --git a/src/urcu-qsbr.c b/src/urcu-qsbr.c
index d69d93b..a338285 100644
--- a/src/urcu-qsbr.c
+++ b/src/urcu-qsbr.c
@@ -123,17 +123,25 @@ static void wait_gp(void)
 {
 	/* Read reader_gp before read futex */
 	cmm_smp_rmb();
-	if (uatomic_read(&urcu_qsbr_gp.futex) != -1)
-		return;
-	while (futex_noasync(&urcu_qsbr_gp.futex, FUTEX_WAIT, -1,
-			NULL, NULL, 0)) {
+	while (uatomic_read(&urcu_qsbr_gp.futex) == -1) {
+		if (!futex_noasync(&urcu_qsbr_gp.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);