Re: [PATCH v5] kthread: Add debugobject support

[Thomas Gleixner]

On Mon, Aug 17 2020 at 14:37, Qianli Zhao wrote:
> From: Qianli Zhao <zhaoqianli@xxxxxxxxxx>
>
> Add debugobject support to track the life time of kthread_work
> which is used to detect reinitialization/free active object problems
> Add kthread_init_work_onstack()/kthread_init_delayed_work_onstack() for
> kthread onstack support
>
> If we reinitialize a kthread_work that has been activated,
> this will cause delayed_work_list/work_list corruption.
> enable this config,there is an chance to fixup these errors
> or WARNING the wrong use of kthread_work
>
> [30858.395766] list_del corruption. next->prev should be ffffffe388ebbf88, but was ffffffe388ebb588
> [30858.395788] WARNING: CPU: 2 PID: 387 at kernel/msm-4.19/lib/list_debug.c:56 __list_del_entry_valid+0xc8/0xd0
> ...
> [30858.395906] Call trace:
> [30858.395909]  __list_del_entry_valid+0xc8/0xd0
> [30858.395912]  __kthread_cancel_work_sync+0x98/0x138
> [30858.395915]  kthread_cancel_delayed_work_sync+0x10/0x20
> [30858.395917]  sde_encoder_resource_control+0xe8/0x12c0
> [30858.395920]  sde_encoder_prepare_for_kickoff+0x5dc/0x2008
> [30858.395923]  sde_crtc_commit_kickoff+0x280/0x890
> [30858.395925]  sde_kms_commit+0x16c/0x278
> [30858.395928]  complete_commit+0x3c4/0x760
> [30858.395931]  _msm_drm_commit_work_cb+0xec/0x1e0
> [30858.395933]  kthread_worker_fn+0xf8/0x190
> [30858.395935]  kthread+0x118/0x128
> [30858.395938]  ret_from_fork+0x10/0x18
>
> crash> struct kthread_worker.delayed_work_list 0xffffffe3893925f0
>  [ffffffe389392620] delayed_work_list = {
>     next = 0xffffffe388ebbf88,
>     prev = 0xffffffe388ebb588
>   }
> crash> list 0xffffffe388ebbf88
> ffffffe388ebbf88

This changelog is confusing at best. Something like this perhaps?

  kthread_work is not covered by debug objects, but the same problems as with
  regular work objects apply.

  Some of the issues like reinitialization of an active kthread_work are hard
  to debug because the problem manifests itself later in a completely
  different context.

  Add debugobject support along with the necessary fixup functions to make
  debugging of these problems less tedious. 

> +static void stub_kthread_work(struct kthread_work *unuse)

unused?

> +{
> +	WARN_ON(1);
> +}
>  void kthread_flush_work(struct kthread_work *work)
>  {
>  	struct kthread_flush_work fwork = {
> -		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
> -		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
> +		.done = COMPLETION_INITIALIZER_ONSTACK(fwork.done),

Eew. Why is the completion initialized seperately instead of being
initialized as part of kthread_init_work_onstack() ?

>  	};
>  	struct kthread_worker *worker;
>  	bool noop = false;
>  
> +	debug_kwork_assert_init(work);
>  	worker = work->worker;
>  	if (!worker)
>  		return;
>  
> +	kthread_init_work_onstack(&fwork.work, kthread_flush_work_fn);
>  
> @@ -1194,12 +1319,13 @@ EXPORT_SYMBOL_GPL(kthread_cancel_delayed_work_sync);
>  void kthread_flush_worker(struct kthread_worker *worker)
>  {
>  	struct kthread_flush_work fwork = {
> -		KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn),
> -		COMPLETION_INITIALIZER_ONSTACK(fwork.done),
> +		.done = COMPLETION_INITIALIZER_ONSTACK(fwork.done),
>  	};

Ditto.
  
> +	kthread_init_work_onstack(&fwork.work, kthread_flush_work_fn);
>  	kthread_queue_work(worker, &fwork.work);
>  	wait_for_completion(&fwork.done);
> +	destroy_kwork_on_stack(&fwork.work);

Thanks,

        tglx