Re: [PATCH 5/6] HMM: add per mirror page table.

[Haggai Eran]

On 06/01/2015 00:44, j.glisse@xxxxxxxxx wrote:
> +	/* fence_wait() - to wait on device driver fence.
> +	 *
> +	 * @fence: The device driver fence struct.
> +	 * Returns: 0 on success,-EIO on error, -EAGAIN to wait again.
> +	 *
> +	 * Called when hmm want to wait for all operations associated with a
> +	 * fence to complete (including device cache flush if the event mandate
> +	 * it).
> +	 *
> +	 * Device driver must free fence and associated resources if it returns
> +	 * something else thant -EAGAIN. On -EAGAIN the fence must not be free
> +	 * as hmm will call back again.
> +	 *
> +	 * Return error if scheduled operation failed or if need to wait again.
> +	 * -EIO Some input/output error with the device.
> +	 * -EAGAIN The fence not yet signaled, hmm reschedule waiting thread.
> +	 *
> +	 * All other return value trigger warning and are transformed to -EIO.
> +	 */
> +	int (*fence_wait)(struct hmm_fence *fence);

According to the comment, the device frees the fence struct when the
fence_wait callback returns zero or -EIO, but the code below calls
fence_unref after fence_wait on the same fence.

> +
> +	/* fence_ref() - take a reference fence structure.
> +	 *
> +	 * @fence: Fence structure hmm is referencing.
> +	 */
> +	void (*fence_ref)(struct hmm_fence *fence);

I don't see fence_ref being called anywhere in the patchset. Is it
actually needed?

> +static void hmm_device_fence_wait(struct hmm_device *device,
> +				  struct hmm_fence *fence)
> +{
> +	struct hmm_mirror *mirror;
> +	int r;
> +
> +	if (fence == NULL)
> +		return;
> +
> +	list_del_init(&fence->list);
> +	do {
> +		r = device->ops->fence_wait(fence);
> +		if (r == -EAGAIN)
> +			io_schedule();
> +	} while (r == -EAGAIN);
> +
> +	mirror = fence->mirror;
> +	device->ops->fence_unref(fence);
> +	if (r)
> +		hmm_mirror_release(mirror);
> +}
> +

Regards,
Haggai
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