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authorRich Felker <dalias@aerifal.cx>2011-08-02 20:31:15 -0400
committerRich Felker <dalias@aerifal.cx>2011-08-02 20:31:15 -0400
commitc68de0be2fb649f91b31080224fb6e48084eaaee (patch)
treed9495283490f37833ca6e32f4b6876ca10ac06eb /src/thread/pthread_mutex_unlock.c
parent344ea148852ed02f280cb92f8fc1611529d60448 (diff)
downloadmusl-c68de0be2fb649f91b31080224fb6e48084eaaee.tar.gz
avoid accessing mutex memory after atomic unlock
this change is needed to fix a race condition and ensure that it's possible to unlock and destroy or unmap the mutex as soon as pthread_mutex_lock succeeds. POSIX explicitly gives such an example in the rationale and requires an implementation to allow such usage.
Diffstat (limited to 'src/thread/pthread_mutex_unlock.c')
-rw-r--r--src/thread/pthread_mutex_unlock.c15
1 files changed, 8 insertions, 7 deletions
diff --git a/src/thread/pthread_mutex_unlock.c b/src/thread/pthread_mutex_unlock.c
index 6c4d7f22..0f4a5e6c 100644
--- a/src/thread/pthread_mutex_unlock.c
+++ b/src/thread/pthread_mutex_unlock.c
@@ -3,6 +3,8 @@
int pthread_mutex_unlock(pthread_mutex_t *m)
{
pthread_t self;
+ int waiters = m->_m_waiters;
+ int cont;
if (m->_m_type != PTHREAD_MUTEX_NORMAL) {
if (!m->_m_lock)
@@ -16,15 +18,14 @@ int pthread_mutex_unlock(pthread_mutex_t *m)
self->robust_list.pending = &m->_m_next;
*(void **)m->_m_prev = m->_m_next;
if (m->_m_next) ((void **)m->_m_next)[-1] = m->_m_prev;
- a_store(&m->_m_lock, 0);
+ cont = a_swap(&m->_m_lock, 0);
self->robust_list.pending = 0;
- } else {
- a_store(&m->_m_lock, 0);
+ goto wake;
}
- } else {
- a_store(&m->_m_lock, 0);
}
-
- if (m->_m_waiters) __wake(&m->_m_lock, 1, 0);
+ cont = a_swap(&m->_m_lock, 0);
+wake:
+ if (waiters || cont<0)
+ __wake(&m->_m_lock, 1, 0);
return 0;
}