atexit.c

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/*
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */
 
/** Macros to abstract Thread Local Storage
 *
 * Simplifies calling thread local destructors (called when the thread exits).
 *
 * @file lib/util/atexit.c
 *
 * @copyright 2020-2021 Arran Cudbard-Bell (a.cudbardb@freeradius.org)
 * @copyright 2020 The FreeRADIUS server project
 */
 
RCSID("$Id: bce89e6227bf06fa14d7a8ac276465d94adee505 $")
 
#include <freeradius-devel/util/debug.h>
#include <freeradius-devel/util/dlist.h>
#include <freeradius-devel/util/atexit.h>
 
#include <stdatomic.h>
 
#ifdef HAVE_PTHREADS
#endif
 
#if defined(DEBUG_ATEXIT) && !defined(NDEBUG)
#  define ATEXIT_DEBUG          FR_FAULT_LOG
#else
#  define ATEXIT_DEBUG(...)
#endif
 
typedef struct fr_exit_handler_list_s fr_atexit_list_t;
 
/** Entry in exit handler list
 *
 */
typedef struct {
        fr_dlist_t                      entry;          //!< Entry in the handler dlist.
        fr_atexit_list_t                *list;          //!< List this entry is in.
 
        fr_atexit_t                     func;           //!< Function to call.
        void                            *uctx;          //!< uctx to pass.
 
        char const                      *file;          //!< File where this exit handler was added.
        int                             line;           //!< Line where this exit handler was added.
} fr_atexit_entry_t;
 
/** Head of a list of exit handlers
 *
 */
struct fr_exit_handler_list_s {
        fr_dlist_head_t                 head;           //!< Head of the list of destructors
 
        pthread_key_t                   key;            //!< Key used to trigger thread local destructors.
        fr_atexit_entry_t               *e;             //!< Inserted into the global exit handler list
                                                        ///< to ensure this memory is cleaned up.
};
 
#ifdef HAVE_PTHREADS
static _Thread_local fr_atexit_list_t   *fr_atexit_thread_local = NULL;
static fr_atexit_list_t                 *fr_atexit_threads = NULL;
static pthread_mutex_t                  fr_atexit_global_mutex = PTHREAD_MUTEX_INITIALIZER;
#endif
 
static fr_atexit_list_t                 *fr_atexit_global = NULL;
static bool                             is_exiting;
static _Thread_local bool               thread_is_exiting;
 
/** Latched once main has decided no more thread-local pools should be handed out
 *
 * `fr_atexit_thread_trigger_all()` runs every registered thread destructor on
 * the calling (main) thread, including ones that free `_Thread_local` pools
 * owned by threads we don't manage (librdkafka's bg threads, perl, etc.).  We
 * can free the underlying chunks but can't reset another thread's TLS slot,
 * so those threads keep a dangling pointer in their per-thread cache.  Code
 * that lazily allocates a TLS-cached pool (log.c, sbuff.c, strerror.c, ...)
 * checks this flag *before* reading its TLS slot and falls back to
 * `talloc_*(NULL, ...)` (or returns NULL) when set, side-stepping the
 * dangling pointer entirely.
 *
 * Set once, never cleared.  Relaxed atomic because this is a one-shot signal
 * with no other state synchronised through it - readers tolerate observing
 * the old value briefly.
 */
static atomic_bool                      thread_local_alloc_disabled;
 
/** Call the exit handler
 *
 */
static int _atexit_entry_free(fr_atexit_entry_t *e)
{
        ATEXIT_DEBUG("%s - Thread %u freeing %p/%p func=%p, uctx=%p (alloced %s:%d)",
                     __FUNCTION__, (unsigned int)pthread_self(),
                     e->list, e, e->func, e->uctx, e->file, e->line);
 
        if (fr_dlist_entry_in_list(&e->entry)) fr_dlist_remove(&e->list->head, e);
 
        /*
         *      If the exit handler wasn't disarmed, call it...
         */
        if (e->func) e->func(e->uctx);
 
        return 0;
}
 
/** Allocate a new exit handler entry
 *
 */
static fr_atexit_entry_t *atexit_entry_alloc(char const *file, int line,
                                             fr_atexit_list_t *list,
                                             fr_atexit_t func, void const *uctx)
{
        fr_atexit_entry_t *e;
 
        e = talloc_zero(list, fr_atexit_entry_t);
        if (unlikely(!e)) return NULL;
 
        e->list = list;
        e->func = func;
        e->uctx = UNCONST(void *, uctx);
        e->file = file;
        e->line = line;
 
        ATEXIT_DEBUG("%s - Thread %u arming %p/%p func=%p, uctx=%p (alloced %s:%d)",
                     __FUNCTION__, (unsigned int)pthread_self(),
                     list, e, e->func, e->uctx, e->file, e->line);
 
        fr_dlist_insert_head(&list->head, e);
        talloc_set_destructor(e, _atexit_entry_free);
 
        return e;
}
 
/** Talloc destructor for freeing list elements in order
 *
 */
static int _destructor_list_free(fr_atexit_list_t *list)
{
        ATEXIT_DEBUG("%s - Freeing destructor list %p", __FUNCTION__, list);
 
        fr_dlist_talloc_free(&list->head);      /* Free in order */
        return 0;
}
 
/** Free any thread-local exit handler lists that pthread_key failed to fre
 *
 */
static void _global_free(void)
{
#ifdef HAVE_PTHREADS
        pthread_mutex_lock(&fr_atexit_global_mutex);
#endif
 
        fr_cond_assert_msg(!is_exiting, "Global free function called multiple times");
        is_exiting = true;
 
#ifdef HAVE_PTHREADS
        pthread_mutex_unlock(&fr_atexit_global_mutex);
        TALLOC_FREE(fr_atexit_threads); /* Forcefully cleanup any thread-specific memory */
#endif
        TALLOC_FREE(fr_atexit_global);
}
 
/** Setup the atexit handler, should be called at the start of a program's execution
 *
 */
int fr_atexit_global_setup(void)
{
        if (fr_atexit_global) return 0;
 
        fr_atexit_global = talloc_zero(NULL, fr_atexit_list_t);
        if (unlikely(!fr_atexit_global)) return -1;
 
        ATEXIT_DEBUG("%s - Alloced global destructor list %p", __FUNCTION__, fr_atexit_global);
 
        fr_dlist_talloc_init(&fr_atexit_global->head, fr_atexit_entry_t, entry);
        talloc_set_destructor(fr_atexit_global, _destructor_list_free);
 
#ifdef HAVE_PTHREADS
        fr_atexit_threads = talloc_zero(NULL, fr_atexit_list_t);
        if (unlikely(!fr_atexit_threads)) {
                TALLOC_FREE(fr_atexit_global);
                return -1;
        }
 
        ATEXIT_DEBUG("%s - Alloced threads destructor list %p", __FUNCTION__, fr_atexit_threads);
 
        fr_dlist_talloc_init(&fr_atexit_threads->head, fr_atexit_entry_t, entry);
        talloc_set_destructor(fr_atexit_threads, _destructor_list_free);
#endif
 
        atexit(_global_free);   /* Call all remaining destructors at process exit */
 
        return 0;
}
 
#ifdef HAVE_PTHREADS
#define CHECK_GLOBAL_SETUP() \
do { \
        int _ret = 0; \
        pthread_mutex_lock(&fr_atexit_global_mutex); \
        fr_cond_assert_msg(!is_exiting, "New atexit handlers should not be allocated whilst exiting"); \
        if (!fr_atexit_global) _ret = fr_atexit_global_setup(); \
        pthread_mutex_unlock(&fr_atexit_global_mutex); \
        if (_ret < 0) return _ret; \
} while(0)
#else
#define CHECK_GLOBAL_SETUP() \
do { \
        int _ret = 0; \
        fr_cond_assert_msg(!is_exiting, "New atexit handlers should not be allocated whilst exiting"); \
        if (!fr_atexit_global) _ret = fr_atexit_global_setup(); \
        if (_ret < 0) return _ret; \
} while(0)
#endif
 
/** Add a free function to be called when the process exits
 *
 */
int _atexit_global(char const *file, int line, fr_atexit_t func, void const *uctx)
{
        CHECK_GLOBAL_SETUP();
 
        if (unlikely(atexit_entry_alloc(file, line, fr_atexit_global, func, uctx) == NULL)) return -1;
 
        return 0;
}
 
/** Remove a specific global destructor (without executing it)
 *
 * @note This function's primary purpose is to help diagnose issues with destructors
 *       from within a debugger.
 *
 * @param[in] uctx_scope        Only process entries where the func and scope both match.
 * @param[in] func              Entries matching this function will be disarmed.
 * @param[in] uctx              associated with the entry.
 * @return How many global destructors were disarmed.
 */
unsigned int fr_atexit_global_disarm(bool uctx_scope, fr_atexit_t func, void const *uctx)
{
        fr_atexit_entry_t       *e = NULL;
        unsigned int            count = 0;
 
        while ((e = fr_dlist_next(&fr_atexit_global->head, e))) {
                fr_atexit_entry_t *disarm;
 
                if ((e->func != func) || ((e->uctx != uctx) && uctx_scope)) continue;
 
                ATEXIT_DEBUG("%s - Disarming %p/%p func=%p, uctx=%p (alloced %s:%d)",
                             __FUNCTION__,
                             fr_atexit_global, e, e->func, e->uctx, e->file, e->line);
 
                disarm = e;
                e = fr_dlist_remove(&fr_atexit_global->head, e);
                talloc_set_destructor(disarm, NULL);
                talloc_free(disarm);
 
                count++;
        }
 
        return count;
}
 
/** Remove all global destructors (without executing them)
 *
 * @note This function's primary purpose is to help diagnose issues with destructors
 *       from within a debugger.
 */
void fr_atexit_global_disarm_all(void)
{
        fr_atexit_entry_t *e = NULL;
 
        if (!fr_atexit_global) return;
 
        while ((e = fr_dlist_pop_head(&fr_atexit_global->head))) {
                ATEXIT_DEBUG("%s - Disarming %p/%p func=%p, uctx=%p (alloced %s:%d)",
                             __FUNCTION__,
                             fr_atexit_global, e, e->func, e->uctx, e->file, e->line);
 
                talloc_set_destructor(e, NULL);
                talloc_free(e);
        }
}
 
/** Cause all global free triggers to fire
 *
 * This is necessary when libraries (perl) register their own
 * atexit handlers using the normal POSIX mechanism, and we need
 * to ensure all our atexit handlers fire before so any global
 * deinit is done explicitly by us.
 *
 * @return
 *      - >= 0 The number of atexit handlers triggered on success.
 *      - <0 the return code from any atexit handlers that returned an error.
 */
int fr_atexit_global_trigger_all(void)
{
        fr_atexit_entry_t               *e = NULL, *to_free;
        unsigned int                    count = 0;
 
        /*
         *      Iterate over the list of thread local
         *      destructor lists running the
         *      destructors.
         */
        while ((e = fr_dlist_next(&fr_atexit_global->head, e))) {
                ATEXIT_DEBUG("%s - Triggering %p/%p func=%p, uctx=%p (alloced %s:%d)",
                             __FUNCTION__,
                             fr_atexit_global, e, e->func, e->uctx, e->file, e->line);
 
                count++;
                to_free = e;
                e = fr_dlist_remove(&fr_atexit_global->head, e);
                if (talloc_free(to_free) < 0) {
                        fr_strerror_printf_push("atexit handler failed %p/%p func=%p, uctx=%p"
                                                " (alloced %s:%d)",
                                                fr_atexit_global, to_free,
                                                to_free->func, to_free->uctx,
                                                to_free->file, to_free->line);
                        return -1;
                }
        }
 
        return count;
}
 
/** Iterates through all thread local destructor lists, causing destructor to be triggered
 *
 * This should only be called by the main process not by threads.
 *
 * The main purpose of the function is to force cleanups at a specific time for problematic
 * destructors.
 *
 * @param[in] uctx_scope        Only process entries where the func and scope both match.
 * @param[in] func              Entries matching this function will be triggered.
 * @param[in] uctx              associated with the entry.
 * @return
 *      - >= 0 The number of atexit handlers triggered on success.
 *      - <0 the return code from any atexit handlers that returned an error.
 */
int fr_atexit_trigger(bool uctx_scope, fr_atexit_t func, void const *uctx)
{
        fr_atexit_entry_t               *e = NULL, *to_free;
#ifdef HAVE_PTHREADS
        fr_atexit_entry_t               *ee;
        fr_atexit_list_t                *list;
#endif
        unsigned int                    count = 0;
 
        if (!fr_atexit_global) goto do_threads;
 
        /*
         *      Iterate over the global destructors
         */
        while ((e = fr_dlist_next(&fr_atexit_global->head, e))) {
                if ((e->func != func) || ((e->uctx != uctx) && uctx_scope)) continue;
 
                ATEXIT_DEBUG("%s - Triggering %p/%p func=%p, uctx=%p (alloced %s:%d)",
                             __FUNCTION__,
                             fr_atexit_global, e, e->func, e->uctx, e->file, e->line);
 
                count++;
                to_free = e;
                e = fr_dlist_remove(&fr_atexit_global->head, e);
                if (talloc_free(to_free) < 0) {
                        fr_strerror_printf_push("atexit handler failed %p/%p func=%p, uctx=%p"
                                                " (alloced %s:%d)",
                                                fr_atexit_global, to_free,
                                                to_free->func, to_free->uctx,
                                                to_free->file, to_free->line);
                        return -1;
                }
        }
        e = NULL;
 
do_threads:
#ifdef HAVE_PTHREADS
        if (!fr_atexit_threads) return 0;
 
        /*
         *      Iterate over the list of thread local
         *      destructor lists running the
         *      destructors.
         */
        while ((e = fr_dlist_next(&fr_atexit_threads->head, e))) {
                if (!e->func) continue; /* thread already joined */
 
                list = talloc_get_type_abort(e->uctx, fr_atexit_list_t);
                ee = NULL;
                while ((ee = fr_dlist_next(&list->head, ee))) {
                        if ((ee->func != func) || ((ee->uctx != uctx) && uctx_scope)) continue;
 
                        ATEXIT_DEBUG("%s - Thread %u triggering %p/%p func=%p, uctx=%p (alloced %s:%d)",
                                     __FUNCTION__,
                                     (unsigned int)pthread_self(),
                                     list, ee, ee->func, ee->uctx, ee->file, ee->line);
 
                        count++;
                        to_free = ee;
                        ee = fr_dlist_remove(&list->head, ee);
                        if (talloc_free(to_free) < 0) {
                                fr_strerror_printf_push("atexit handler failed %p/%p func=%p, uctx=%p"
                                                        " (alloced %s:%d)",
                                                        list, to_free,
                                                        to_free->func, to_free->uctx,
                                                        to_free->file, to_free->line);
                                return -1;
                        }
                }
        }
#endif
 
        return count;
}
 
 
/** Disable lazy allocation of thread-local caches for the rest of the process
 *
 * Call this from main *before* `fr_atexit_thread_trigger_all()`.  After it
 * returns, every TLS-pool initialiser that consults
 * `fr_atexit_thread_local_alloc_disabled()` falls back to the un-cached path,
 * so `_Thread_local` slots in other threads aren't read after the trigger
 * frees their backing memory.
 */
void fr_atexit_thread_local_disable_alloc(void)
{
        atomic_store_explicit(&thread_local_alloc_disabled, true, memory_order_relaxed);
}
 
/** Has @ref fr_atexit_thread_local_disable_alloc been called yet
 *
 */
bool fr_atexit_thread_local_alloc_disabled(void)
{
        return atomic_load_explicit(&thread_local_alloc_disabled, memory_order_relaxed);
}
 
/** Return whether we're currently in the teardown phase
 *
 * When this function returns true no more thread local or global
 * destructors can be added.
 */
bool fr_atexit_is_exiting(void)
{
#ifdef HAVE_PTHREADS
        bool save_is_exiting;
 
        pthread_mutex_lock(&fr_atexit_global_mutex);
        save_is_exiting = is_exiting;
        pthread_mutex_unlock(&fr_atexit_global_mutex);
 
        return save_is_exiting;
#else
        return is_exiting;
#endif
}
 
#ifdef HAVE_PTHREADS
/** Talloc destructor for freeing list elements in order
 *
 */
static int _thread_local_list_free(fr_atexit_list_t *list)
{
        ATEXIT_DEBUG("%s - Freeing _Thread_local destructor list %p",  __FUNCTION__, list);
 
        fr_dlist_talloc_free(&list->head);      /* Free in order */
        pthread_mutex_lock(&fr_atexit_global_mutex);
        list->e->func = NULL;                   /* Disarm the global entry that'd free the thread-specific list */
        pthread_mutex_unlock(&fr_atexit_global_mutex);
        return 0;
}
 
/** Run all the thread local destructors
 *
 * @param[in] list      The thread-specific exit handler list.
 */
static void _thread_local_pthread_free(void *list)
{
        talloc_free(list);
}
 
/** Run all the thread local destructors
 *
 * @param[in] list      The thread-specific exit handler list.
 */
static int _thread_local_free(void *list)
{
        thread_is_exiting = true;
        return talloc_free(list);
}
 
/** Add a new destructor
 *
 * @return
 *      - 0 on success.
 *      - -1 on memory allocation failure;
 */
int _fr_atexit_thread_local(char const *file, int line,
                            fr_atexit_t func, void const *uctx)
{
        CHECK_GLOBAL_SETUP();
 
        /*
         *      Initialise the thread local list, just for pthread_exit().
         */
        if (!fr_atexit_thread_local) {
                fr_atexit_list_t *list;
 
                /*
                 *      Must be heap allocated, because thread local
                 *      structures can be freed before the key
                 *      destructor is run (depending on platform).
                 */
                list = talloc_zero(NULL, fr_atexit_list_t);
                if (unlikely(!list)) return -1;
 
                ATEXIT_DEBUG("%s - Thread %u alloced _Thread_local destructor list %p",
                             __FUNCTION__,
                             (unsigned int)pthread_self(), list);
 
                fr_dlist_talloc_init(&list->head, fr_atexit_entry_t, entry);
                (void) pthread_key_create(&list->key, _thread_local_pthread_free);
 
                /*
                 *      We need to pass in a pointer to the heap
                 *      memory because, again, the thread local
                 *      indirection table may have disappeared
                 *      by the time the thread destructor is
                 *      called.
                 */
                (void) pthread_setspecific(list->key, list);
                talloc_set_destructor(list, _thread_local_list_free);
 
                /*
                 *      Add a destructor for the thread-local list
                 *      The pthread based destructor will disarm
                 *      this if it fires, but leave it enabled if
                 *      it doesn't, thus ensuring the memory is
                 *      *always* freed one way or another.
                 */
                pthread_mutex_lock(&fr_atexit_global_mutex);
                list->e = atexit_entry_alloc(file, line,
                                             fr_atexit_threads,
                                             _thread_local_free,
                                             list);
 
                pthread_mutex_unlock(&fr_atexit_global_mutex);
 
                fr_atexit_thread_local = list;
        }
 
        /*
         *      Now allocate the actual atexit handler entry
         */
        if (atexit_entry_alloc(file, line, fr_atexit_thread_local, func, uctx) == NULL) return -1;
 
        return 0;
}
 
/** Remove a specific destructor for this thread (without executing them)
 *
 * @note This function's primary purpose is to help diagnose issues with destructors
 *       from within a debugger.
 *
 * @param[in] uctx_scope        Only process entries where the func and scope both match.
 * @param[in] func              Entries matching this function will be disarmed.
 * @param[in] uctx              associated with the entry.
 * @return How many destructors were disarmed.
 */
unsigned int fr_atexit_thread_local_disarm(bool uctx_scope, fr_atexit_t func, void const *uctx)
{
        fr_atexit_entry_t       *e = NULL;
        unsigned int            count = 0;
 
        if (!fr_atexit_thread_local) return 0;
 
        while ((e = fr_dlist_next(&fr_atexit_thread_local->head, e))) {
                fr_atexit_entry_t *disarm;
 
                if ((e->func != func) || ((e->uctx != uctx) && uctx_scope)) continue;
 
                ATEXIT_DEBUG("%s - Thread %u disarming %p/%p func=%p, uctx=%p (alloced %s:%d)",
                             __FUNCTION__,
                             (unsigned int)pthread_self(),
                             fr_atexit_thread_local, e, e->func, e->uctx, e->file, e->line);
                disarm = e;
                e = fr_dlist_remove(&fr_atexit_thread_local->head, e);
                talloc_set_destructor(disarm, NULL);
                talloc_free(disarm);
 
                count++;
        }
 
        return count;
}
 
/** Remove all destructors for this thread (without executing them)
 *
 * @note This function's primary purpose is to help diagnose issues with destructors
 *       from within a debugger.
 */
void fr_atexit_thread_local_disarm_all(void)
{
        fr_atexit_entry_t *e = NULL;
 
        if (!fr_atexit_thread_local) return;
 
        while ((e = fr_dlist_pop_head(&fr_atexit_thread_local->head))) {
                ATEXIT_DEBUG("%s - Thread %u disarming %p/%p func=%p, uctx=%p (alloced %s:%d)",
                             __FUNCTION__,
                             (unsigned int)pthread_self(),
                             fr_atexit_thread_local, e, e->func, e->uctx, e->file, e->line);
                talloc_set_destructor(e, NULL);
                talloc_free(e);
        }
}
 
/** Cause all thread local free triggers to fire
 *
 * This is necessary when we're running in single threaded mode
 * to ensure all "thread-local" memory (which isn't actually thread local)
 * is cleaned up.
 *
 * One example is the OpenSSL log BIOs which must be cleaned up
 * before fr_openssl_free is called.
 *
 * @return
 *      - >= 0 The number of atexit handlers triggered on success.
 *      - <0 the return code from any atexit handlers that returned an error.
 */
int fr_atexit_thread_trigger_all(void)
{
        fr_atexit_entry_t               *e = NULL, *ee, *to_free;
        fr_atexit_list_t                *list;
        unsigned int                    count = 0;
 
        /*
         *      Disable TLS-cached pool handouts before we start freeing
         *      any of them.  Threads we don't manage (librdkafka's bg
         *      threads, etc.) keep dangling pointers in their
         *      `_Thread_local` slots once the chunks here are reaped, so
         *      any TLS-pool initialiser that consults the flag falls back
         *      to `talloc_*(NULL, ...)` from now on.
         */
        fr_atexit_thread_local_disable_alloc();
 
        /*
         *      Iterate over the list of thread local
         *      destructor lists running the
         *      destructors.
         */
        while ((e = fr_dlist_next(&fr_atexit_threads->head, e))) {
                if (!e->func) continue; /* thread already joined */
 
                list = talloc_get_type_abort(e->uctx, fr_atexit_list_t);
                ee = NULL;
                while ((ee = fr_dlist_next(&list->head, ee))) {
                        ATEXIT_DEBUG("%s - Thread %u triggering %p/%p func=%p, uctx=%p (alloced %s:%d)",
                                     __FUNCTION__,
                                     (unsigned int)pthread_self(),
                                     list, ee, ee->func, ee->uctx, ee->file, ee->line);
 
                        count++;
                        to_free = ee;
                        ee = fr_dlist_remove(&list->head, ee);
                        if (talloc_free(to_free) < 0) {
                                fr_strerror_printf_push("atexit handler failed %p/%p func=%p, uctx=%p"
                                                        " (alloced %s:%d)",
                                                        list, to_free,
                                                        to_free->func, to_free->uctx,
                                                        to_free->file, to_free->line
                                                        );
                                return -1;
                        }
                }
        }
 
        return count;
}
 
/** Return whether the thread is currently being cleaned up
 *
 */
bool fr_atexit_thread_is_exiting(void)
{
        return thread_is_exiting;
}
#endif