Use proper memory ordering for tasks_running/tasks_ready

diff --git a/lib/isc/task.c b/lib/isc/task.c
index 87ece27ec09470184b68d1fb657a2ac2e31365e0..55418590bf3c86b5292efeffc2e14d4bb4f3ac5c 100644 (file)
--- a/lib/isc/task.c
+++ b/lib/isc/task.c
@@ -915,7 +915,8 @@ push_readyq(isc__taskmgr_t *manager, isc__task_t *task, int c) {
        if ((task->flags & TASK_F_PRIVILEGED) != 0)
                ENQUEUE(manager->queues[c].ready_priority_tasks, task,
                        ready_priority_link);
-       atomic_fetch_add_explicit(&manager->tasks_ready, 1, memory_order_relaxed);
+       atomic_fetch_add_explicit(&manager->tasks_ready, 1,
+                                 memory_order_acquire);
 }
 
 static void
@@ -1051,13 +1052,15 @@ dispatch(isc__taskmgr_t *manager, unsigned int threadid) {
                        INSIST(VALID_TASK(task));
 
                        /*
-                        * Note we only unlock the manager lock if we actually
-                        * have a task to do.  We must reacquire the manager
+                        * Note we only unlock the queue lock if we actually
+                        * have a task to do.  We must reacquire the queue
                         * lock before exiting the 'if (task != NULL)' block.
                         */
                        UNLOCK(&manager->queues[threadid].lock);
-                       atomic_fetch_add_explicit(&manager->tasks_ready, -1, memory_order_relaxed);
-                       atomic_fetch_add_explicit(&manager->tasks_running, 1, memory_order_relaxed);
+                       RUNTIME_CHECK(atomic_fetch_sub_explicit(&manager->tasks_ready,
+                                                 1, memory_order_release) > 0);
+                       atomic_fetch_add_explicit(&manager->tasks_running, 1,
+                                                 memory_order_acquire);
 
                        LOCK(&task->lock);
                        INSIST(task->state == task_state_ready);
@@ -1171,7 +1174,8 @@ dispatch(isc__taskmgr_t *manager, unsigned int threadid) {
                        if (finished)
                                task_finished(task);
 
-                       atomic_fetch_add_explicit(&manager->tasks_running, -1, memory_order_relaxed);
+                       RUNTIME_CHECK(atomic_fetch_sub_explicit(&manager->tasks_running,
+                                               1, memory_order_release) > 0);
                        LOCK(&manager->queues[threadid].lock);
                        if (requeue) {
                                /*
@@ -1203,7 +1207,10 @@ dispatch(isc__taskmgr_t *manager, unsigned int threadid) {
                 * we're stuck.  Automatically drop privileges at that
                 * point and continue with the regular ready queue.
                 */
-               if (atomic_load(&manager->tasks_running) == 0 && manager->mode != isc_taskmgrmode_normal) {
+               if (atomic_load_explicit(&manager->tasks_running,
+                                        memory_order_acquire) == 0 &&
+                   manager->mode != isc_taskmgrmode_normal)
+               {
                        bool empty = true;
                        for (unsigned i=0; i<manager->workers && empty; i++) {
                                if (i != threadid) {