gpu: nvgpu: mark thread stopped when it independently quits

It's technically possible for a thread to exit without first calling
nvgpu_thread_stop() in another, so mark the thread exit status from the
thread after it has finished instead of in nvgpu_thread_stop(). Do this
by starting the thread as a proxy function which calls the actual thread
function and then sets the flag.

Also, add a new flag to actually signify the running state because the
thread->task going null abruptly would break nvgpu_thread_stop().

This does not guarantee that the kernel thread itself has stopped, but
the function which can be considered as an "nvgpu thread" will be.

Change-Id: Ib911b02bd51342ddeb8e6b9533ef7943f2606d2d
Signed-off-by: Konsta Holtta <kholtta@nvidia.com>
Reviewed-on: http://git-master/r/1501571
Reviewed-by: Mahantesh Kumbar <mkumbar@nvidia.com>
Reviewed-by: Alex Waterman <alexw@nvidia.com>
Reviewed-by: svccoveritychecker <svccoveritychecker@nvidia.com>
GVS: Gerrit_Virtual_Submit
Reviewed-by: Vijayakumar Subbu <vsubbu@nvidia.com>

drivers/gpu/nvgpu/common/linux/thread.c

@@ -18,15 +18,28 @@
 
 #include <nvgpu/thread.h>
 
+int nvgpu_thread_proxy(void *threaddata)
+{
+	struct nvgpu_thread *thread = threaddata;
+	int ret = thread->fn(thread->data);
+
+	thread->running = false;
+	return ret;
+}
+
 int nvgpu_thread_create(struct nvgpu_thread *thread,
 		void *data,
 		int (*threadfn)(void *data), const char *name)
 {
-	struct task_struct *task = kthread_create(threadfn, data, name);
+	struct task_struct *task = kthread_create(nvgpu_thread_proxy,
+			thread, name);
 	if (IS_ERR(task))
 		return PTR_ERR(task);
 
 	thread->task = task;
+	thread->fn = threadfn;
+	thread->data = data;
+	thread->running = true;
 	wake_up_process(task);
 	return 0;
 };
@@ -44,5 +57,5 @@ bool nvgpu_thread_should_stop(struct nvgpu_thread *thread)
 
 bool nvgpu_thread_is_running(struct nvgpu_thread *thread)
 {
-	return thread->task != NULL;
+	return ACCESS_ONCE(thread->running);
 };