v3dv: lock around noop job submits

Any thread we create may end up creating/submitting at least a
noop job, which is a shared object. Before multisync, this was
an issue only for the creation of the job itself, but with
multisync we can also modify parameters of the noop job
every time it is used (for signaling and serialization
configuration).

This change adds a noop mutex that all threads (main, wait and
master) take before submitting a noop job to ensure concurrent
access is not an issue.

Fixes flakyness observed with multisync with the following test:
dEQP-VK.api.command_buffers.secondary_execute_twice

Reviewed-by: Melissa Wen <mwen@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15342>

src/broadcom/vulkan/v3dv_device.c

@@ -1827,6 +1827,7 @@ queue_init(struct v3dv_device *device, struct v3dv_queue *queue,
    queue->noop_job = NULL;
    list_inithead(&queue->submit_wait_list);
    pthread_mutex_init(&queue->mutex, NULL);
+   pthread_mutex_init(&queue->noop_mutex, NULL);
    return VK_SUCCESS;
 }
 
@@ -1838,6 +1839,7 @@ queue_finish(struct v3dv_queue *queue)
    if (queue->noop_job)
       v3dv_job_destroy(queue->noop_job);
    pthread_mutex_destroy(&queue->mutex);
+   pthread_mutex_destroy(&queue->noop_mutex);
 }
 
 static void

src/broadcom/vulkan/v3dv_private.h

@@ -260,6 +260,9 @@ struct v3dv_queue {
    /* A mutex to prevent concurrent access to the list of wait threads */
    mtx_t mutex;
 
+   /* A mutex to prevent concurrent noop job submissions */
+   mtx_t noop_mutex;
+
    struct v3dv_job *noop_job;
 };
 

src/broadcom/vulkan/v3dv_queue.c

@@ -1228,18 +1228,26 @@ queue_submit_noop_job(struct v3dv_queue *queue,
    if (!do_sem_signal && !serialize && !sems_info->wait_sem_count)
       return VK_SUCCESS;
 
-   /* VkQueue host access is externally synchronized so we don't need to lock
-    * here for the static variable.
+   /* We need to protect noop_job against concurrent access. While
+    * the client must externally synchronize queue submissions, we
+    * may spawn threads that can submit noop jobs themselves.
     */
+   mtx_lock(&queue->noop_mutex);
    if (!queue->noop_job) {
       VkResult result = queue_create_noop_job(queue);
-      if (result != VK_SUCCESS)
+      if (result != VK_SUCCESS) {
+         mtx_unlock(&queue->noop_mutex);
          return result;
+      }
    }
    queue->noop_job->do_sem_signal = do_sem_signal;
    queue->noop_job->serialize = serialize;
 
-   return queue_submit_job(queue, queue->noop_job, sems_info, NULL);
+   VkResult result =
+      queue_submit_job(queue, queue->noop_job, sems_info, NULL);
+
+   mtx_unlock(&queue->noop_mutex);
+   return result;
 }
 
 /* This function takes a job type and returns True if we have