/*
- * Copyright (C) 2012 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
+ * Copyright (C) 2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
*
- * This program is free software; you can redistribute it and/or modify it
- * under the terms of the GNU Lesser General Public License, version 2.1 only,
- * as published by the Free Software Foundation.
+ * SPDX-License-Identifier: LGPL-2.1-only
*
- * This program is distributed in the hope that it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
- * for more details.
- *
- * You should have received a copy of the GNU Lesser General Public License
- * along with this program; if not, write to the Free Software Foundation,
- * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
- * This code is originally adapted from userspace-rcu's urcu-wait.h
*/
#include "waiter.h"
}
caa_cpu_relax();
}
- while (futex_noasync(&waiter->state, FUTEX_WAIT, WAITER_WAITING,
- NULL, NULL, 0)) {
+ while (uatomic_read(&waiter->state) == WAITER_WAITING) {
+ if (!futex_noasync(&waiter->state, FUTEX_WAIT, WAITER_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
+ * WAITER_WAITING (spurious wakeups). Check
+ * the value again in user-space to validate
+ * whether it really differs from WAITER_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. */
PERROR("futex_noasync");