Module Name: src
Committed By: sborrill
Date: Thu Feb 20 13:00:40 UTC 2014
Modified Files:
src/lib/libpthread [netbsd-6]: pthread_cond.c pthread_mutex.c
Log Message:
Pull up the following revisions(s) (requested by prlw1 in ticket #1029):
lib/libpthread/pthread_cond.c: revision 1.62
lib/libpthread/pthread_mutex.c: revision 1.57,1.59
Partial fix for thread deadlock commonly observed with named.
Also address PR/44756.
To generate a diff of this commit:
cvs rdiff -u -r1.56.8.3 -r1.56.8.4 src/lib/libpthread/pthread_cond.c
cvs rdiff -u -r1.51.22.1 -r1.51.22.2 src/lib/libpthread/pthread_mutex.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/lib/libpthread/pthread_cond.c
diff -u src/lib/libpthread/pthread_cond.c:1.56.8.3 src/lib/libpthread/pthread_cond.c:1.56.8.4
--- src/lib/libpthread/pthread_cond.c:1.56.8.3 Mon Apr 29 01:50:18 2013
+++ src/lib/libpthread/pthread_cond.c Thu Feb 20 13:00:40 2014
@@ -1,4 +1,4 @@
-/* $NetBSD: pthread_cond.c,v 1.56.8.3 2013/04/29 01:50:18 riz Exp $ */
+/* $NetBSD: pthread_cond.c,v 1.56.8.4 2014/02/20 13:00:40 sborrill Exp $ */
/*-
* Copyright (c) 2001, 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -46,7 +46,7 @@
*/
#include <sys/cdefs.h>
-__RCSID("$NetBSD: pthread_cond.c,v 1.56.8.3 2013/04/29 01:50:18 riz Exp $");
+__RCSID("$NetBSD: pthread_cond.c,v 1.56.8.4 2014/02/20 13:00:40 sborrill Exp $");
#include <errno.h>
#include <sys/time.h>
@@ -181,10 +181,12 @@ pthread_cond_timedwait(pthread_cond_t *c
pthread_mutex_unlock(mutex);
self->pt_willpark = 0;
self->pt_blocking++;
- retval = _lwp_park(abstime, self->pt_unpark,
- __UNVOLATILE(&mutex->ptm_waiters),
- __UNVOLATILE(&mutex->ptm_waiters));
- self->pt_unpark = 0;
+ do {
+ retval = _lwp_park(abstime, self->pt_unpark,
+ __UNVOLATILE(&mutex->ptm_waiters),
+ __UNVOLATILE(&mutex->ptm_waiters));
+ self->pt_unpark = 0;
+ } while (retval == -1 && errno == ESRCH);
self->pt_blocking--;
membar_sync();
pthread_mutex_lock(mutex);
Index: src/lib/libpthread/pthread_mutex.c
diff -u src/lib/libpthread/pthread_mutex.c:1.51.22.1 src/lib/libpthread/pthread_mutex.c:1.51.22.2
--- src/lib/libpthread/pthread_mutex.c:1.51.22.1 Mon Apr 29 01:50:18 2013
+++ src/lib/libpthread/pthread_mutex.c Thu Feb 20 13:00:40 2014
@@ -1,4 +1,4 @@
-/* $NetBSD: pthread_mutex.c,v 1.51.22.1 2013/04/29 01:50:18 riz Exp $ */
+/* $NetBSD: pthread_mutex.c,v 1.51.22.2 2014/02/20 13:00:40 sborrill Exp $ */
/*-
* Copyright (c) 2001, 2003, 2006, 2007, 2008 The NetBSD Foundation, Inc.
@@ -47,7 +47,7 @@
*/
#include <sys/cdefs.h>
-__RCSID("$NetBSD: pthread_mutex.c,v 1.51.22.1 2013/04/29 01:50:18 riz Exp $");
+__RCSID("$NetBSD: pthread_mutex.c,v 1.51.22.2 2014/02/20 13:00:40 sborrill Exp $");
#include <sys/types.h>
#include <sys/lwpctl.h>
@@ -211,11 +211,61 @@ pthread__mutex_spin(pthread_mutex_t *ptm
return owner;
}
+NOINLINE static void
+pthread__mutex_setwaiters(pthread_t self, pthread_mutex_t *ptm)
+{
+ void *new, *owner;
+
+ /*
+ * Note that the mutex can become unlocked before we set
+ * the waiters bit. If that happens it's not safe to sleep
+ * as we may never be awoken: we must remove the current
+ * thread from the waiters list and try again.
+ *
+ * Because we are doing this atomically, we can't remove
+ * one waiter: we must remove all waiters and awken them,
+ * then sleep in _lwp_park() until we have been awoken.
+ *
+ * Issue a memory barrier to ensure that we are reading
+ * the value of ptm_owner/pt_mutexwait after we have entered
+ * the waiters list (the CAS itself must be atomic).
+ */
+again:
+ membar_consumer();
+ owner = ptm->ptm_owner;
+
+ if (MUTEX_OWNER(owner) == 0) {
+ pthread__mutex_wakeup(self, ptm);
+ return;
+ }
+ if (!MUTEX_HAS_WAITERS(owner)) {
+ new = (void *)((uintptr_t)owner | MUTEX_WAITERS_BIT);
+ if (atomic_cas_ptr(&ptm->ptm_owner, owner, new) != owner) {
+ goto again;
+ }
+ }
+
+ /*
+ * Note that pthread_mutex_unlock() can do a non-interlocked CAS.
+ * We cannot know if the presence of the waiters bit is stable
+ * while the holding thread is running. There are many assumptions;
+ * see sys/kern/kern_mutex.c for details. In short, we must spin if
+ * we see that the holder is running again.
+ */
+ membar_sync();
+ pthread__mutex_spin(ptm, owner);
+
+ if (membar_consumer(), !MUTEX_HAS_WAITERS(ptm->ptm_owner)) {
+ goto again;
+ }
+}
+
NOINLINE static int
pthread__mutex_lock_slow(pthread_mutex_t *ptm)
{
void *waiters, *new, *owner, *next;
pthread_t self;
+ int serrno;
pthread__error(EINVAL, "Invalid mutex",
ptm->ptm_magic == _PT_MUTEX_MAGIC);
@@ -235,6 +285,7 @@ pthread__mutex_lock_slow(pthread_mutex_t
return EDEADLK;
}
+ serrno = errno;
for (;; owner = ptm->ptm_owner) {
/* Spin while the owner is running. */
owner = pthread__mutex_spin(ptm, owner);
@@ -247,6 +298,7 @@ pthread__mutex_lock_slow(pthread_mutex_t
next = atomic_cas_ptr(&ptm->ptm_owner, owner,
new);
if (next == owner) {
+ errno = serrno;
#ifndef PTHREAD__ATOMIC_IS_MEMBAR
membar_enter();
#endif
@@ -277,48 +329,8 @@ pthread__mutex_lock_slow(pthread_mutex_t
break;
}
- /*
- * Set the waiters bit and block.
- *
- * Note that the mutex can become unlocked before we set
- * the waiters bit. If that happens it's not safe to sleep
- * as we may never be awoken: we must remove the current
- * thread from the waiters list and try again.
- *
- * Because we are doing this atomically, we can't remove
- * one waiter: we must remove all waiters and awken them,
- * then sleep in _lwp_park() until we have been awoken.
- *
- * Issue a memory barrier to ensure that we are reading
- * the value of ptm_owner/pt_mutexwait after we have entered
- * the waiters list (the CAS itself must be atomic).
- */
- membar_consumer();
- for (owner = ptm->ptm_owner;; owner = next) {
- if (MUTEX_HAS_WAITERS(owner))
- break;
- if (MUTEX_OWNER(owner) == 0) {
- pthread__mutex_wakeup(self, ptm);
- break;
- }
- new = (void *)((uintptr_t)owner | MUTEX_WAITERS_BIT);
- next = atomic_cas_ptr(&ptm->ptm_owner, owner, new);
- if (next == owner) {
- /*
- * pthread_mutex_unlock() can do a
- * non-interlocked CAS. We cannot
- * know if our attempt to set the
- * waiters bit has succeeded while
- * the holding thread is running.
- * There are many assumptions; see
- * sys/kern/kern_mutex.c for details.
- * In short, we must spin if we see
- * that the holder is running again.
- */
- membar_sync();
- next = pthread__mutex_spin(ptm, owner);
- }
- }
+ /* Set the waiters bit and block. */
+ pthread__mutex_setwaiters(self, ptm);
/*
* We may have been awoken by the current thread above,
