path: root/src/thread/pthread_mutex_unlock.c
diff options
authorRich Felker <>2014-08-16 19:52:04 -0400
committerRich Felker <>2014-08-16 19:52:04 -0400
commitd338b506e39b1e2c68366b12be90704c635602ce (patch)
treea73ff388f254f21d4f6be5b9985b37ae8309679e /src/thread/pthread_mutex_unlock.c
parentfffc5cda10e0c5c910b40f7be0d4fa4e15bb3f48 (diff)
fix robust mutex unrecoverable status, and related clean-up
a robust mutex should not enter the unrecoverable status until it's unlocked without marking it consistent. previously, flag 8 in the type was used as an indication of unrecoverable, but only honored after successful locking; this resulted in a race window where the unrecoverable mutex could appear to a second thread as locked/busy again while the first thread was in the process of observing it as unrecoverable. now, flag 8 is used to mean that the mutex is in the process of being recovered, but not yet marked consistent. the flag only takes effect in pthread_mutex_unlock, where it causes the value 0x40000000 (owner dead flag, with old owner tid 0, an otherwise impossible state) to be stored in the lock. subsequent lock attempts will interpret this state as unrecoverable.
Diffstat (limited to 'src/thread/pthread_mutex_unlock.c')
1 files changed, 1 insertions, 3 deletions
diff --git a/src/thread/pthread_mutex_unlock.c b/src/thread/pthread_mutex_unlock.c
index b4ed3f87..42837516 100644
--- a/src/thread/pthread_mutex_unlock.c
+++ b/src/thread/pthread_mutex_unlock.c
@@ -12,8 +12,6 @@ int pthread_mutex_unlock(pthread_mutex_t *m)
int priv = (m->_m_type & 128) ^ 128;
- if (!m->_m_lock)
- return EPERM;
self = __pthread_self();
if ((m->_m_lock&0x7fffffff) != self->tid)
return EPERM;
@@ -26,7 +24,7 @@ int pthread_mutex_unlock(pthread_mutex_t *m)
*(void **)m->_m_prev = m->_m_next;
if (m->_m_next) ((void **)m->_m_next)[-1] = m->_m_prev;
- cont = a_swap(&m->_m_lock, 0);
+ cont = a_swap(&m->_m_lock, (type & 8) ? 0x40000000 : 0);
if (type != PTHREAD_MUTEX_NORMAL && !priv) {
self->robust_list.pending = 0;