+// SPDX-FileCopyrightText: 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+// SPDX-FileCopyrightText: 2009 Paul E. McKenney, IBM Corporation.
+//
+// SPDX-License-Identifier: LGPL-2.1-or-later
+
#ifndef _URCU_DEFER_IMPL_H
#define _URCU_DEFER_IMPL_H
/*
- * urcu-defer-impl.h
- *
* Userspace RCU header - memory reclamation.
*
* TO BE INCLUDED ONLY FROM URCU LIBRARY CODE. See urcu-defer.h for linking
* dynamically with the userspace rcu reclamation library.
*
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
- * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Lesser General Public
- * License as published by the Free Software Foundation; either
- * version 2.1 of the License, or (at your option) any later version.
- *
- * This library 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 library; if not, write to the Free Software
- * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
- *
* IBM's contributions to this file may be relicensed under LGPLv2 or later.
*/
uatomic_set(&defer_thread_futex, 0);
} else {
cmm_smp_rmb(); /* Read queue before read futex */
- if (uatomic_read(&defer_thread_futex) != -1)
- return;
- while (futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
- NULL, NULL, 0)) {
+ while (uatomic_read(&defer_thread_futex) == -1) {
+ if (!futex_noasync(&defer_thread_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);
static void start_defer_thread(void)
{
int ret;
+ sigset_t newmask, oldmask;
+
+ ret = sigfillset(&newmask);
+ urcu_posix_assert(!ret);
+ ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+ urcu_posix_assert(!ret);
ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
+ if (ret)
+ urcu_die(ret);
+
+ ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
urcu_posix_assert(!ret);
}