From f97d673f9b1aee1626b0b3c702e4406f0c140979 Mon Sep 17 00:00:00 2001 From: Jakub Wartak Date: Tue, 8 Sep 2026 12:44:55 +0200 Subject: [PATCH v4 04/21] port: Detect mutex misuse in assertion-enabled builds. In assertion-enabled builds, make pg_mtx_init() create error-checking mutexes when plain ones are requested, and use the glibc error-checking static initializer for PG_MTX_PLAIN_INIT where it exists. Then assert in pg_mtx_lock() and pg_mtx_unlock() that the operation succeeded. Few callers check those results, so without the assertions an error-checking mutex would turn a self-deadlock into a silently ignored EDEADLK rather than a crash with a stack trace. Only the pthread implementation is affected. Windows SRWLOCKs can't detect these mistakes, and statically initialized mutexes stay unchecked on non-glibc systems. Author: Jakub Wartak Co-authored-by: Greg Burd Discussion: https://postgr.es/m/CAKZiRmw3gpoXeOc9Pa_PRpfp-bTeQhg6gaY2Jw0Ck6NX4PWPhQ%40mail.gmail.com --- src/include/port/pg_threads/map_pthread.h | 29 +++++++++++++++++++ src/include/port/pg_threads/map_pthread_ext.h | 5 ++++ src/port/pg_threads.c | 4 +++ 3 files changed, 38 insertions(+) diff --git a/src/include/port/pg_threads/map_pthread.h b/src/include/port/pg_threads/map_pthread.h index ccb5a2f906f..2a7e57e96f9 100644 --- a/src/include/port/pg_threads/map_pthread.h +++ b/src/include/port/pg_threads/map_pthread.h @@ -80,14 +80,43 @@ PG_THREADS_MAP(pg_cnd_wait, pthread_cond_wait, pg_cnd_impl *, pg_mtx_impl *); /* mtx_t */ PG_THREADS_FORWARD_VOID(pg_mtx_destroy, pthread_mutex_destroy, pg_mtx_impl *); PG_THREADS_OUTOFLINE(pg_mtx_init, int, pg_mtx_impl *, int); +#ifndef USE_ASSERT_CHECKING PG_THREADS_MAP(pg_mtx_lock, pthread_mutex_lock, pg_mtx_impl *); +#else +/* + * In assertion-enabled builds, pg_mtx_init() and PG_MTX_PLAIN_INIT ask for + * error-checking mutexes where available. Callers rarely check the result + * of locking and unlocking, so assert success here instead, turning a + * self-deadlock or an unlock by the wrong thread into a crash with a stack + * trace. + */ +static inline int +pg_mtx_lock(pg_mtx_impl *mtx) +{ + int result = pthread_mutex_lock(mtx); + + Assert(result == 0); + return pg_thrd_map(result); +} +#endif #ifndef PG_MTX_TIMED_NOT_SUPPORTED PG_THREADS_MAP(pg_mtx_timedlock, pthread_mutex_timedlock, pg_mtx_impl *, const struct timespec *); #else PG_THREADS_MAP_ERROR_UNSUPPORTED(pg_mtx_timedlock, pg_mtx_impl *, const struct timespec *); #endif PG_THREADS_MAP(pg_mtx_trylock, pthread_mutex_trylock, pg_mtx_impl *); +#ifndef USE_ASSERT_CHECKING PG_THREADS_MAP(pg_mtx_unlock, pthread_mutex_unlock, pg_mtx_impl *); +#else +static inline int +pg_mtx_unlock(pg_mtx_impl *mtx) +{ + int result = pthread_mutex_unlock(mtx); + + Assert(result == 0); + return pg_thrd_map(result); +} +#endif /* once_flag */ PG_THREADS_FORWARD_VOID(pg_call_once, pthread_once, pg_once_flag_impl *, pg_call_once_function_impl); diff --git a/src/include/port/pg_threads/map_pthread_ext.h b/src/include/port/pg_threads/map_pthread_ext.h index 4ebdc6bb5f6..d3d53d0d138 100644 --- a/src/include/port/pg_threads/map_pthread_ext.h +++ b/src/include/port/pg_threads/map_pthread_ext.h @@ -45,8 +45,13 @@ enum #ifndef PG_THREADS_USE_THREADS_H #define PG_CND_INIT_IMPL PTHREAD_COND_INITIALIZER +#if defined(USE_ASSERT_CHECKING) && defined(PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP) +/* A glibc extension. Elsewhere, static mutexes don't check for misuse. */ +#define PG_MTX_PLAIN_INIT_IMPL PTHREAD_ERRORCHECK_MUTEX_INITIALIZER_NP +#else #define PG_MTX_PLAIN_INIT_IMPL PTHREAD_MUTEX_INITIALIZER #endif +#endif #define PG_RWLOCK_PLAIN_INIT_IMPL PTHREAD_RWLOCK_INITIALIZER /* pg_rwlock_t */ diff --git a/src/port/pg_threads.c b/src/port/pg_threads.c index 922060a2d5e..173d6a574fb 100644 --- a/src/port/pg_threads.c +++ b/src/port/pg_threads.c @@ -361,6 +361,10 @@ pg_mtx_init_impl(pg_mtx_impl *mtx, int type) pthread_mutexattr_init(&attr); if (type & pg_mtx_recursive_impl) pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE); +#ifdef USE_ASSERT_CHECKING + else + pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_ERRORCHECK); +#endif result = pg_thrd_map(pthread_mutex_init(mtx, &attr)); pthread_mutexattr_destroy(&attr); -- 2.54.0