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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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22
src/thread/pthread_mutex_timedlock.c
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@ -2,15 +2,23 @@
int pthread_mutex_timedlock(pthread_mutex_t *m, const struct timespec *at)
{
int r, w=0;
int r, t;
if (m->_m_type == PTHREAD_MUTEX_NORMAL && !a_cas(&m->_m_lock, 0, EBUSY))
return 0;
while ((r=pthread_mutex_trylock(m)) == EBUSY) {
if (!(r=m->_m_lock) || (r&0x40000000)) continue;
if (!w) a_inc(&m->_m_waiters), w++;
if (__timedwait(&m->_m_lock, r, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
if (w) a_dec(&m->_m_waiters);
return ETIMEDOUT;
}
if ((m->_m_type&3) == PTHREAD_MUTEX_ERRORCHECK
&& (r&0x1fffffff) == pthread_self()->tid)
return EDEADLK;
a_inc(&m->_m_waiters);
t = r | 0x80000000;
a_cas(&m->_m_lock, r, t);
r = __timedwait(&m->_m_lock, t, CLOCK_REALTIME, at, 0);
a_dec(&m->_m_waiters);
if (r && r != EINTR) break;
}
if (w) a_dec(&m->_m_waiters);
return r;
}