X-Git-Url: http://plrg.eecs.uci.edu/git/?p=c11tester.git;a=blobdiff_plain;f=model.cc;h=ae3788945c7756881178b1657bb215cf5a71901a;hp=400adc208047f8d2c7b4700c31bc20b650854e34;hb=0b3c8355b0f1fdf7e4b983bef11472192405a9d9;hpb=82df62c2b0805848b87bb71df5b66a4a66f8e25d diff --git a/model.cc b/model.cc index 400adc20..ae378894 100644 --- a/model.cc +++ b/model.cc @@ -39,7 +39,6 @@ struct bug_message { */ struct model_snapshot_members { model_snapshot_members() : - current_action(NULL), /* First thread created will have id INITIAL_THREAD_ID */ next_thread_id(INITIAL_THREAD_ID), used_sequence_numbers(0), @@ -59,7 +58,6 @@ struct model_snapshot_members { bugs.clear(); } - ModelAction *current_action; unsigned int next_thread_id; modelclock_t used_sequence_numbers; ModelAction *next_backtrack; @@ -161,6 +159,14 @@ void ModelChecker::reset_to_initial_state() /* Print all model-checker output before rollback */ fflush(model_out); + /** + * FIXME: if we utilize partial rollback, we will need to free only + * those pending actions which were NOT pending before the rollback + * point + */ + for (unsigned int i = 0; i < get_num_threads(); i++) + delete get_thread(int_to_id(i))->get_pending(); + snapshot_backtrack_before(0); } @@ -205,11 +211,14 @@ Node * ModelChecker::get_curr_node() const * adjacency of read/write portions of a RMW action, force THREAD_CREATE to be * followed by a THREAD_START, or it can enforce execution replay/backtracking. * The model-checker may have no preference regarding the next thread (i.e., - * when exploring a new execution ordering), in which case this will return - * NULL. - * @param curr The current ModelAction. This action might guide the choice of - * next thread. - * @return The next thread to run. If the model-checker has no preference, NULL. + * when exploring a new execution ordering), in which case we defer to the + * scheduler. + * + * @param curr Optional: The current ModelAction. Only used if non-NULL and it + * might guide the choice of next thread (i.e., THREAD_CREATE should be + * followed by THREAD_START, or ATOMIC_RMWR followed by ATOMIC_{RMW,RMWC}) + * @return The next chosen thread to run, if any exist. Or else if no threads + * remain to be executed, return NULL. */ Thread * ModelChecker::get_next_thread(ModelAction *curr) { @@ -218,14 +227,17 @@ Thread * ModelChecker::get_next_thread(ModelAction *curr) if (curr != NULL) { /* Do not split atomic actions. */ if (curr->is_rmwr()) - return thread_current(); + return get_thread(curr); else if (curr->get_type() == THREAD_CREATE) return curr->get_thread_operand(); } - /* Have we completed exploring the preselected path? */ + /* + * Have we completed exploring the preselected path? Then let the + * scheduler decide + */ if (diverge == NULL) - return NULL; + return scheduler->select_next_thread(); /* Else, we are trying to replay an execution */ ModelAction *next = node_stack->get_next()->get_action(); @@ -295,23 +307,47 @@ void ModelChecker::execute_sleep_set() for (unsigned int i = 0; i < get_num_threads(); i++) { thread_id_t tid = int_to_id(i); Thread *thr = get_thread(tid); - if (scheduler->is_sleep_set(thr) && thr->get_pending() == NULL) { - scheduler->next_thread(thr); - Thread::swap(&system_context, thr); - priv->current_action->set_sleep_flag(); - thr->set_pending(priv->current_action); + if (scheduler->is_sleep_set(thr) && thr->get_pending()) { + thr->get_pending()->set_sleep_flag(); } } } +/** + * @brief Should the current action wake up a given thread? + * + * @param curr The current action + * @param thread The thread that we might wake up + * @return True, if we should wake up the sleeping thread; false otherwise + */ +bool ModelChecker::should_wake_up(const ModelAction *curr, const Thread *thread) const +{ + const ModelAction *asleep = thread->get_pending(); + /* Don't allow partial RMW to wake anyone up */ + if (curr->is_rmwr()) + return false; + /* Synchronizing actions may have been backtracked */ + if (asleep->could_synchronize_with(curr)) + return true; + /* All acquire/release fences and fence-acquire/store-release */ + if (asleep->is_fence() && asleep->is_acquire() && curr->is_release()) + return true; + /* Fence-release + store can awake load-acquire on the same location */ + if (asleep->is_read() && asleep->is_acquire() && curr->same_var(asleep) && curr->is_write()) { + ModelAction *fence_release = get_last_fence_release(curr->get_tid()); + if (fence_release && *(get_last_action(thread->get_id())) < *fence_release) + return true; + } + return false; +} + void ModelChecker::wake_up_sleeping_actions(ModelAction *curr) { for (unsigned int i = 0; i < get_num_threads(); i++) { Thread *thr = get_thread(int_to_id(i)); if (scheduler->is_sleep_set(thr)) { - ModelAction *pending_act = thr->get_pending(); - if ((!curr->is_rmwr()) && pending_act->could_synchronize_with(curr)) - //Remove this thread from sleep set + if (should_wake_up(curr, thr)) + /* Remove this thread from sleep set */ scheduler->remove_sleep(thr); } } @@ -324,11 +360,22 @@ void ModelChecker::set_bad_synchronization() priv->bad_synchronization = true; } +/** + * Check whether the current trace has triggered an assertion which should halt + * its execution. + * + * @return True, if the execution should be aborted; false otherwise + */ bool ModelChecker::has_asserted() const { return priv->asserted; } +/** + * Trigger a trace assertion which should cause this execution to be halted. + * This can be due to a detected bug or due to an infeasibility that should + * halt ASAP. + */ void ModelChecker::set_assert() { priv->asserted = true; @@ -525,25 +572,118 @@ bool ModelChecker::next_execution() return true; } -ModelAction * ModelChecker::get_last_conflict(ModelAction *act) +/** + * @brief Find the last fence-related backtracking conflict for a ModelAction + * + * This function performs the search for the most recent conflicting action + * against which we should perform backtracking, as affected by fence + * operations. This includes pairs of potentially-synchronizing actions which + * occur due to fence-acquire or fence-release, and hence should be explored in + * the opposite execution order. + * + * @param act The current action + * @return The most recent action which conflicts with act due to fences + */ +ModelAction * ModelChecker::get_last_fence_conflict(ModelAction *act) const +{ + /* Only perform release/acquire fence backtracking for stores */ + if (!act->is_write()) + return NULL; + + /* Find a fence-release (or, act is a release) */ + ModelAction *last_release; + if (act->is_release()) + last_release = act; + else + last_release = get_last_fence_release(act->get_tid()); + if (!last_release) + return NULL; + + /* Skip past the release */ + action_list_t *list = action_trace; + action_list_t::reverse_iterator rit; + for (rit = list->rbegin(); rit != list->rend(); rit++) + if (*rit == last_release) + break; + ASSERT(rit != list->rend()); + + /* Find a prior: + * load-acquire + * or + * load --sb-> fence-acquire */ + std::vector< ModelAction *, ModelAlloc > acquire_fences(get_num_threads(), NULL); + std::vector< ModelAction *, ModelAlloc > prior_loads(get_num_threads(), NULL); + bool found_acquire_fences = false; + for ( ; rit != list->rend(); rit++) { + ModelAction *prev = *rit; + if (act->same_thread(prev)) + continue; + + int tid = id_to_int(prev->get_tid()); + + if (prev->is_read() && act->same_var(prev)) { + if (prev->is_acquire()) { + /* Found most recent load-acquire, don't need + * to search for more fences */ + if (!found_acquire_fences) + return NULL; + } else { + prior_loads[tid] = prev; + } + } + if (prev->is_acquire() && prev->is_fence() && !acquire_fences[tid]) { + found_acquire_fences = true; + acquire_fences[tid] = prev; + } + } + + ModelAction *latest_backtrack = NULL; + for (unsigned int i = 0; i < acquire_fences.size(); i++) + if (acquire_fences[i] && prior_loads[i]) + if (!latest_backtrack || *latest_backtrack < *acquire_fences[i]) + latest_backtrack = acquire_fences[i]; + return latest_backtrack; +} + +/** + * @brief Find the last backtracking conflict for a ModelAction + * + * This function performs the search for the most recent conflicting action + * against which we should perform backtracking. This primary includes pairs of + * synchronizing actions which should be explored in the opposite execution + * order. + * + * @param act The current action + * @return The most recent action which conflicts with act + */ +ModelAction * ModelChecker::get_last_conflict(ModelAction *act) const { switch (act->get_type()) { - case ATOMIC_FENCE: + /* case ATOMIC_FENCE: fences don't directly cause backtracking */ case ATOMIC_READ: case ATOMIC_WRITE: case ATOMIC_RMW: { - /* Optimization: relaxed operations don't need backtracking */ - if (act->is_relaxed()) - return NULL; + ModelAction *ret = NULL; + /* linear search: from most recent to oldest */ action_list_t *list = get_safe_ptr_action(obj_map, act->get_location()); action_list_t::reverse_iterator rit; for (rit = list->rbegin(); rit != list->rend(); rit++) { ModelAction *prev = *rit; - if (prev->could_synchronize_with(act)) - return prev; + if (prev->could_synchronize_with(act)) { + ret = prev; + break; + } } - break; + + ModelAction *ret2 = get_last_fence_conflict(act); + if (!ret2) + return ret; + if (!ret) + return ret2; + if (*ret < *ret2) + return ret2; + return ret; } case ATOMIC_LOCK: case ATOMIC_TRYLOCK: { @@ -1215,16 +1355,6 @@ bool ModelChecker::check_action_enabled(ModelAction *curr) { return true; } -/** - * Stores the ModelAction for the current thread action. Call this - * immediately before switching from user- to system-context to pass - * data between them. - * @param act The ModelAction created by the user-thread action - */ -void ModelChecker::set_current_action(ModelAction *act) { - priv->current_action = act; -} - /** * This is the heart of the model checker routine. It performs model-checking * actions corresponding to a given "current action." Among other processes, it @@ -1263,7 +1393,7 @@ ModelAction * ModelChecker::check_current_action(ModelAction *curr) /* Build may_read_from set for newly-created actions */ if (newly_explored && curr->is_read()) - build_reads_from_past(curr); + build_may_read_from(curr); /* Initialize work_queue with the "current action" work */ work_queue_t work_queue(1, CheckCurrWorkEntry(curr)); @@ -1860,7 +1990,7 @@ bool ModelChecker::release_seq_heads(const ModelAction *rf, if (mo_graph->checkForCycles()) return false; - while (rf) { + for ( ; rf != NULL; rf = rf->get_reads_from()) { ASSERT(rf->is_write()); if (rf->is_release()) @@ -1880,8 +2010,6 @@ bool ModelChecker::release_seq_heads(const ModelAction *rf, /* acq_rel RMW is a sufficient stopping condition */ if (rf->is_acquire() && rf->is_release()) return true; /* complete */ - - rf = rf->get_reads_from(); }; if (!rf) { /* read from future: need to settle this later */ @@ -2440,12 +2568,12 @@ void ModelChecker::compute_relseq_breakwrites(ModelAction *curr) /** * Build up an initial set of all past writes that this 'read' action may read - * from. This set is determined by the clock vector's "happens before" - * relationship. + * from, as well as any previously-observed future values that must still be valid. + * * @param curr is the current ModelAction that we are exploring; it must be a * 'read' operation. */ -void ModelChecker::build_reads_from_past(ModelAction *curr) +void ModelChecker::build_may_read_from(ModelAction *curr) { std::vector *thrd_lists = get_safe_ptr_vect_action(obj_thrd_map, curr->get_location()); unsigned int i; @@ -2490,8 +2618,25 @@ void ModelChecker::build_reads_from_past(ModelAction *curr) break; } } + + /* Inherit existing, promised future values */ + for (i = 0; i < promises->size(); i++) { + const Promise *promise = (*promises)[i]; + const ModelAction *promise_read = promise->get_action(); + if (promise_read->same_var(curr)) { + /* Only add feasible future-values */ + mo_graph->startChanges(); + r_modification_order(curr, promise); + if (!is_infeasible()) { + const struct future_value fv = promise->get_fv(); + curr->get_node()->add_future_value(fv); + } + mo_graph->rollbackChanges(); + } + } + /* We may find no valid may-read-from only if the execution is doomed */ - if (!curr->get_node()->get_read_from_size()) { + if (!curr->get_node()->get_read_from_size() && curr->get_node()->future_value_empty()) { priv->no_valid_reads = true; set_assert(); } @@ -2507,7 +2652,7 @@ void ModelChecker::build_reads_from_past(ModelAction *curr) bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *write) { - while (true) { + for ( ; write != NULL; write = write->get_reads_from()) { /* UNINIT actions don't have a Node, and they never sleep */ if (write->is_uninitialized()) return true; @@ -2516,13 +2661,10 @@ bool ModelChecker::sleep_can_read_from(ModelAction *curr, const ModelAction *wri bool thread_sleep = prevnode->enabled_status(curr->get_tid()) == THREAD_SLEEP_SET; if (write->is_release() && thread_sleep) return true; - if (!write->is_rmw()) { + if (!write->is_rmw()) return false; - } - if (write->get_reads_from() == NULL) - return true; - write = write->get_reads_from(); } + return true; } /** @@ -2663,6 +2805,19 @@ bool ModelChecker::is_enabled(thread_id_t tid) const return scheduler->is_enabled(tid); } +/** + * Switch from a model-checker context to a user-thread context. This is the + * complement of ModelChecker::switch_to_master and must be called from the + * model-checker context + * + * @param thread The user-thread to switch to + */ +void ModelChecker::switch_from_master(Thread *thread) +{ + scheduler->set_current_thread(thread); + Thread::swap(&system_context, thread); +} + /** * Switch from a user-context to the "master thread" context (a.k.a. system * context). This switch is made with the intention of exploring a particular @@ -2678,7 +2833,8 @@ uint64_t ModelChecker::switch_to_master(ModelAction *act) { DBG(); Thread *old = thread_current(); - set_current_action(act); + ASSERT(!old->get_pending()); + old->set_pending(act); if (Thread::swap(old, &system_context) < 0) { perror("swap threads"); exit(EXIT_FAILURE); @@ -2689,13 +2845,11 @@ uint64_t ModelChecker::switch_to_master(ModelAction *act) /** * Takes the next step in the execution, if possible. * @param curr The current step to take - * @return Returns true (success) if a step was taken and false otherwise. + * @return Returns the next Thread to run, if any; NULL if this execution + * should terminate */ -bool ModelChecker::take_step(ModelAction *curr) +Thread * ModelChecker::take_step(ModelAction *curr) { - if (has_asserted()) - return false; - Thread *curr_thrd = get_thread(curr); ASSERT(curr_thrd->get_state() == THREAD_READY); @@ -2703,58 +2857,24 @@ bool ModelChecker::take_step(ModelAction *curr) /* Infeasible -> don't take any more steps */ if (is_infeasible()) - return false; + return NULL; else if (isfeasibleprefix() && have_bug_reports()) { set_assert(); - return false; + return NULL; } - if (params.bound != 0) - if (priv->used_sequence_numbers > params.bound) - return false; + if (params.bound != 0 && priv->used_sequence_numbers > params.bound) + return NULL; if (curr_thrd->is_blocked() || curr_thrd->is_complete()) scheduler->remove_thread(curr_thrd); Thread *next_thrd = get_next_thread(curr); - next_thrd = scheduler->next_thread(next_thrd); DEBUG("(%d, %d)\n", curr_thrd ? id_to_int(curr_thrd->get_id()) : -1, next_thrd ? id_to_int(next_thrd->get_id()) : -1); - /* - * Launch end-of-execution release sequence fixups only when there are: - * - * (1) no more user threads to run (or when execution replay chooses - * the 'model_thread') - * (2) pending release sequences - * (3) pending assertions (i.e., data races) - * (4) no pending promises - */ - if (!pending_rel_seqs->empty() && (!next_thrd || next_thrd->is_model_thread()) && - is_feasible_prefix_ignore_relseq() && !unrealizedraces.empty()) { - model_print("*** WARNING: release sequence fixup action (%zu pending release seuqences) ***\n", - pending_rel_seqs->size()); - ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ, - std::memory_order_seq_cst, NULL, VALUE_NONE, - model_thread); - set_current_action(fixup); - return true; - } - - /* next_thrd == NULL -> don't take any more steps */ - if (!next_thrd) - return false; - - if (next_thrd->get_pending() != NULL) { - /* restart a pending action */ - set_current_action(next_thrd->get_pending()); - next_thrd->set_pending(NULL); - return true; - } - - /* Return false only if swap fails with an error */ - return (Thread::swap(&system_context, next_thrd) == 0); + return next_thrd; } /** Wrapper to run the user's main function, with appropriate arguments */ @@ -2769,16 +2889,56 @@ void ModelChecker::run() do { thrd_t user_thread; Thread *t = new Thread(&user_thread, &user_main_wrapper, NULL); - add_thread(t); - /* Run user thread up to its first action */ - scheduler->next_thread(t); - Thread::swap(&system_context, t); + do { + /* + * Stash next pending action(s) for thread(s). There + * should only need to stash one thread's action--the + * thread which just took a step--plus the first step + * for any newly-created thread + */ + for (unsigned int i = 0; i < get_num_threads(); i++) { + thread_id_t tid = int_to_id(i); + Thread *thr = get_thread(tid); + if (!thr->is_model_thread() && !thr->is_complete() && !thr->get_pending()) { + switch_from_master(thr); + } + } - /* Wait for all threads to complete */ - while (take_step(priv->current_action)); + /* Catch assertions from prior take_step or from + * between-ModelAction bugs (e.g., data races) */ + if (has_asserted()) + break; + + /* Consume the next action for a Thread */ + ModelAction *curr = t->get_pending(); + t->set_pending(NULL); + t = take_step(curr); + } while (t && !t->is_model_thread()); + + /* + * Launch end-of-execution release sequence fixups only when + * the execution is otherwise feasible AND there are: + * + * (1) pending release sequences + * (2) pending assertions that could be invalidated by a change + * in clock vectors (i.e., data races) + * (3) no pending promises + */ + while (!pending_rel_seqs->empty() && + is_feasible_prefix_ignore_relseq() && + !unrealizedraces.empty()) { + model_print("*** WARNING: release sequence fixup action " + "(%zu pending release seuqence(s)) ***\n", + pending_rel_seqs->size()); + ModelAction *fixup = new ModelAction(MODEL_FIXUP_RELSEQ, + std::memory_order_seq_cst, NULL, VALUE_NONE, + model_thread); + take_step(fixup); + }; } while (next_execution()); + model_print("******* Model-checking complete: *******\n"); print_stats(); }