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Date: Wed, 27 Aug 2014 11:56:22 +0200
From: Jens Gustedt <Jens.Gustedt@...ia.fr>
To: musl@...ts.openwall.com
Subject: [PATCH 1/2] Let the signaler do all work concerning consistency of
the list
---
src/thread/pthread_cond_timedwait.c | 31 ++++++++++++++++++++++---------
1 file changed, 22 insertions(+), 9 deletions(-)
diff --git a/src/thread/pthread_cond_timedwait.c b/src/thread/pthread_cond_timedwait.c
index 2d192b0..52b1026 100644
--- a/src/thread/pthread_cond_timedwait.c
+++ b/src/thread/pthread_cond_timedwait.c
@@ -84,18 +84,26 @@ static void unwait(void *arg)
* via the futex notify below. */
pthread_cond_t *c = node->cond;
+ int * ref;
+
lock(&c->_c_lock);
-
- if (c->_c_head == node) c->_c_head = node->next;
- else if (node->prev) node->prev->next = node->next;
- if (c->_c_tail == node) c->_c_tail = node->prev;
- else if (node->next) node->next->prev = node->prev;
-
+ /* Our membership to the list may have changed while waiting for the lock. */
+ /* Ensure that the notify field is only read while we hold the lock. */
+ ref = node->notify;
+
+ /* If there has been no race with a signaler, splice us out of the list. */
+ /* Otherwise, the signaler has already taken care of it. */
+ if (!ref) {
+ if (c->_c_head == node) c->_c_head = node->next;
+ else if (node->prev) node->prev->next = node->next;
+ if (c->_c_tail == node) c->_c_tail = node->prev;
+ else if (node->next) node->next->prev = node->prev;
+ }
unlock(&c->_c_lock);
- if (node->notify) {
- if (a_fetch_add(node->notify, -1)==1)
- __wake(node->notify, 1, 1);
+ if (ref) {
+ if (a_fetch_add(ref, -1)==1)
+ __wake(ref, 1, 1);
}
} else {
/* Lock barrier first to control wake order. */
@@ -172,6 +180,11 @@ int __private_cond_signal(pthread_cond_t *c, int n)
if (a_cas(&p->state, WAITING, SIGNALED) != WAITING) {
ref++;
p->notify = &ref;
+ /* Let the signaler do all work concerning consistency of the list. */
+ if (c->_c_head == p) c->_c_head = p->next;
+ else if (p->prev) p->prev->next = p->next;
+ if (c->_c_tail == p) c->_c_tail = p->prev;
+ else if (p->next) p->next->prev = p->prev;
} else {
n--;
if (!first) first=p;
--
1.7.10.4
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