linux-kernel - Re: [PATCH] dma-buf/sync_file: only enable fence signalling during wait

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Date:	Sun, 10 Jul 2016 11:15:52 +0200
From:	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
To:	Gustavo Padovan <gustavo@...ovan.org>,
	dri-devel@...ts.freedesktop.org
Cc:	linux-kernel@...r.kernel.org, Daniel Stone <daniels@...labora.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Rob Clark <robdclark@...il.com>,
	Greg Hackmann <ghackmann@...gle.com>,
	John Harrison <John.C.Harrison@...el.com>,
	laurent.pinchart@...asonboard.com, seanpaul@...gle.com,
	marcheu@...gle.com, m.chehab@...sung.com,
	Sumit Semwal <sumit.semwal@...aro.org>,
	Gustavo Padovan <gustavo.padovan@...labora.co.uk>
Subject: Re: [PATCH] dma-buf/sync_file: only enable fence signalling during
 wait

Op 08-07-16 om 17:44 schreef Gustavo Padovan:
> From: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
>
> Signalling doesn't need to be enabled at sync_file creation, it is only
> required if userspace waiting the fence to signal through poll().
>
> Thus we delay fence_add_callback() until poll is called. It only adds the
> callback the first time poll() is called. This avoid re-adding the same
> callback multiple times.
>
> v2: rebase and update to work with new fence support for sync_file
>
> Signed-off-by: Gustavo Padovan <gustavo.padovan@...labora.co.uk>
> ---
> This patch applies on top of my latest sync_file changes to support
> fence_array: https://lkml.org/lkml/2016/7/4/534
>
>  drivers/dma-buf/sync_file.c | 23 ++++++++++++++---------
>  include/linux/sync_file.h   |  2 ++
>  2 files changed, 16 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
> index 61a687c..1db4a64 100644
> --- a/drivers/dma-buf/sync_file.c
> +++ b/drivers/dma-buf/sync_file.c
> @@ -86,8 +86,6 @@ struct sync_file *sync_file_create(struct fence *fence)
>  		 fence->ops->get_timeline_name(fence), fence->context,
>  		 fence->seqno);
>  
> -	fence_add_callback(fence, &sync_file->cb, fence_check_cb_func);
> -
>  	return sync_file;
>  }
>  EXPORT_SYMBOL(sync_file_create);
> @@ -269,9 +267,6 @@ static struct sync_file *sync_file_merge(const char *name, struct sync_file *a,
>  		goto err;
>  	}
>  
> -	fence_add_callback(sync_file->fence, &sync_file->cb,
> -			   fence_check_cb_func);
> -
>  	strlcpy(sync_file->name, name, sizeof(sync_file->name));
>  	return sync_file;
>  
> @@ -286,7 +281,6 @@ static void sync_file_free(struct kref *kref)
>  	struct sync_file *sync_file = container_of(kref, struct sync_file,
>  						     kref);
>  
> -	fence_remove_callback(sync_file->fence, &sync_file->cb);
>  	fence_put(sync_file->fence);
>  	kfree(sync_file);
>  }
> @@ -306,13 +300,24 @@ static unsigned int sync_file_poll(struct file *file, poll_table *wait)
>  
>  	poll_wait(file, &sync_file->wq, wait);
>  
> +	if (!sync_file->enabled) {
> +		fence_add_callback(sync_file->fence, &sync_file->cb,
> +				   fence_check_cb_func);
> +		sync_file->enabled = true;
> +	}
Won't this blow up completely with 2 threads polling at the same time?

~Maarten