diff options
Diffstat (limited to 'src/lib/lock')
-rw-r--r-- | src/lib/lock/compat_mutex.c | 12 | ||||
-rw-r--r-- | src/lib/lock/compat_mutex.h | 9 | ||||
-rw-r--r-- | src/lib/lock/compat_mutex_pthreads.c | 24 | ||||
-rw-r--r-- | src/lib/lock/compat_mutex_winthreads.c | 2 | ||||
-rw-r--r-- | src/lib/lock/include.am | 2 | ||||
-rw-r--r-- | src/lib/lock/lib_lock.md | 6 |
6 files changed, 48 insertions, 7 deletions
diff --git a/src/lib/lock/compat_mutex.c b/src/lib/lock/compat_mutex.c index 4ad5929715..b0084a3484 100644 --- a/src/lib/lock/compat_mutex.c +++ b/src/lib/lock/compat_mutex.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 */ /** @@ -29,7 +29,15 @@ tor_mutex_new_nonrecursive(void) tor_mutex_init_nonrecursive(m); return m; } -/** Release all storage and system resources held by <b>m</b>. */ +/** Release all storage and system resources held by <b>m</b>. + * + * 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_free_(tor_mutex_t *m) { diff --git a/src/lib/lock/compat_mutex.h b/src/lib/lock/compat_mutex.h index b63ce24024..5631993cc4 100644 --- a/src/lib/lock/compat_mutex.h +++ b/src/lib/lock/compat_mutex.h @@ -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 */ /** @@ -48,7 +48,7 @@ typedef struct tor_mutex_t { #else /** No-threads only: Dummy variable so that tor_mutex_t takes up space. */ int _unused; -#endif /* defined(USE_WIN32_MUTEX) || ... */ +#endif /* defined(USE_WIN32_THREADS) || ... */ } tor_mutex_t; tor_mutex_t *tor_mutex_new(void); @@ -58,6 +58,11 @@ void tor_mutex_init_nonrecursive(tor_mutex_t *m); void tor_mutex_acquire(tor_mutex_t *m); void tor_mutex_release(tor_mutex_t *m); void tor_mutex_free_(tor_mutex_t *m); +/** + * @copydoc tor_mutex_free_ + * + * Additionally, set the pointer <b>m</b> to NULL. + **/ #define tor_mutex_free(m) FREE_AND_NULL(tor_mutex_t, tor_mutex_free_, (m)) void tor_mutex_uninit(tor_mutex_t *m); 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 diff --git a/src/lib/lock/compat_mutex_winthreads.c b/src/lib/lock/compat_mutex_winthreads.c index b0f5999e42..5fe6870a93 100644 --- a/src/lib/lock/compat_mutex_winthreads.c +++ b/src/lib/lock/compat_mutex_winthreads.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 */ /** diff --git a/src/lib/lock/include.am b/src/lib/lock/include.am index 4e6f444347..1475b9911b 100644 --- a/src/lib/lock/include.am +++ b/src/lib/lock/include.am @@ -5,6 +5,7 @@ if UNITTESTS_ENABLED noinst_LIBRARIES += src/lib/libtor-lock-testing.a endif +# ADD_C_FILE: INSERT SOURCES HERE. src_lib_libtor_lock_a_SOURCES = \ src/lib/lock/compat_mutex.c @@ -20,5 +21,6 @@ src_lib_libtor_lock_testing_a_SOURCES = \ src_lib_libtor_lock_testing_a_CPPFLAGS = $(AM_CPPFLAGS) $(TEST_CPPFLAGS) src_lib_libtor_lock_testing_a_CFLAGS = $(AM_CFLAGS) $(TEST_CFLAGS) +# ADD_C_FILE: INSERT HEADERS HERE. noinst_HEADERS += \ src/lib/lock/compat_mutex.h diff --git a/src/lib/lock/lib_lock.md b/src/lib/lock/lib_lock.md new file mode 100644 index 0000000000..6f6727bfc2 --- /dev/null +++ b/src/lib/lock/lib_lock.md @@ -0,0 +1,6 @@ +@dir /lib/lock +@brief lib/lock: Simple locking support. + +This module is more low-level than the rest of the threading code, since it +is needed by more intermediate-level modules. + |