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avoid accessing mutex memory after atomic unlock

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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.
This commit is contained in:
Rich Felker
2011-08-02 20:31:15 -04:00
parent 344ea14885
commit c68de0be2f
4 changed files with 31 additions and 34 deletions
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14
src/thread/pthread_mutex_trylock.c
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@ -2,15 +2,14 @@
int pthread_mutex_trylock(pthread_mutex_t *m)
{
int tid;
int own;
int tid, old, own;
pthread_t self;
if (m->_m_type == PTHREAD_MUTEX_NORMAL)
return a_swap(&m->_m_lock, EBUSY);
return a_cas(&m->_m_lock, 0, EBUSY) & EBUSY;
self = pthread_self();
tid = self->tid | 0x80000000;
tid = self->tid;
if (m->_m_type >= 4) {
if (!self->robust_list.off)
@ -20,14 +19,15 @@ int pthread_mutex_trylock(pthread_mutex_t *m)
self->robust_list.pending = &m->_m_next;
}
if (m->_m_lock == tid && (m->_m_type&3) == PTHREAD_MUTEX_RECURSIVE) {
old = m->_m_lock;
own = old & 0x7fffffff;
if (own == tid && (m->_m_type&3) == PTHREAD_MUTEX_RECURSIVE) {
if ((unsigned)m->_m_count >= INT_MAX) return EAGAIN;
m->_m_count++;
return 0;
}
own = m->_m_lock;
if ((own && !(own & 0x40000000)) || a_cas(&m->_m_lock, own, tid)!=own)
if ((own && !(own & 0x40000000)) || a_cas(&m->_m_lock, old, tid)!=old)
return EBUSY;
m->_m_count = 1;