diff options
Diffstat (limited to 'src/lib/lock/compat_mutex_pthreads.c')
| -rw-r--r-- | src/lib/lock/compat_mutex_pthreads.c | 24 |
1 files changed, 22 insertions, 2 deletions
diff --git a/src/lib/lock/compat_mutex_pthreads.c b/src/lib/lock/compat_mutex_pthreads.c index ee5f520cd0..ac83c42a47 100644 --- a/src/lib/lock/compat_mutex_pthreads.c +++ b/src/lib/lock/compat_mutex_pthreads.c @@ -1,6 +1,6 @@ /* Copyright (c) 2003-2004, Roger Dingledine * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. - * Copyright (c) 2007-2019, The Tor Project, Inc. */ + * Copyright (c) 2007-2020, The Tor Project, Inc. */ /* See LICENSE for licensing information */ /** @@ -17,8 +17,14 @@ * "recursive" mutexes (i.e., once we can re-lock if we're already holding * them.) */ static pthread_mutexattr_t attr_recursive; +/** + * True iff <b>attr_recursive</b> has been initialized. + **/ static int attr_initialized = 0; +/** + * Initialize the locking module, if it is not already initialized. + **/ void tor_locking_init(void) { @@ -88,12 +94,26 @@ tor_mutex_release(tor_mutex_t *m) } /** Clean up the mutex <b>m</b> so that it no longer uses any system * resources. Does not free <b>m</b>. This function must only be called on - * mutexes from tor_mutex_init(). */ + * mutexes from tor_mutex_init(). + * + * Destroying a locked mutex is undefined behaviour. Global mutexes may be + * locked when they are passed to this function, because multiple threads can + * still access them. So we can either: + * - destroy on shutdown, and re-initialise when tor re-initialises, or + * - skip destroying and re-initialisation, using a sentinel variable. + * See #31735 for details. + */ void tor_mutex_uninit(tor_mutex_t *m) { int err; raw_assert(m); + /* If the mutex is already locked, wait until after it is unlocked to destroy + * it. Locking and releasing the mutex makes undefined behaviour less likely, + * but does not prevent it. Another thread can lock the mutex between release + * and destroy. */ + tor_mutex_acquire(m); + tor_mutex_release(m); err = pthread_mutex_destroy(&m->mutex); if (PREDICT_UNLIKELY(err)) { // LCOV_EXCL_START |