On Mon, Jan 22, 2024 at 07:07:21PM +0800, Yi Sun wrote:
> In some cases, it is necessary to wait for all requests to become complete
> status before performing other operations. Otherwise, these requests will never
> be processed successfully.
>
> For example, when the virtio device is in hibernation, the virtqueues
> will be deleted. It must be ensured that virtqueue is not in use before being deleted.
> Otherwise the requests in the virtqueue will be lost. This function can ensure
> that all requests have been taken out of the virtqueues.
>
> Prepare for fixing this kind of issue by introducing
> blk_mq_tagset_wait_request_completed().
Does blk_mq_freeze_queue() not work for your use case? I think that
should work unless you have some driver specific requests entered that
don't ever get released.
> +static bool blk_mq_tagset_count_inflight_rqs(struct request *rq, void *data)
> +{
> + unsigned int *count = data;
> +
> + if (blk_mq_request_started(rq) && !blk_mq_request_completed(rq))
> + (*count)++;
> + return true;
> +}
> +
> +/**
> + * blk_mq_tagset_wait_request_completed - Wait for all inflight requests
> + * to become completed.
> + *
> + * Note: This function has to be run after all IO queues are shutdown.
> + */
> +void blk_mq_tagset_wait_request_completed(struct blk_mq_tag_set *tagset)
> +{
> + while (true) {
> + unsigned int count = 0;
> +
> + blk_mq_tagset_busy_iter(tagset,
> + blk_mq_tagset_count_inflight_rqs, &count);
If the tagset is shared, then one active user can prevent this from ever
completing. It sounds like your use case cares about just one specific
request_queue, not all of them.
> + if (!count)
> + break;
> + msleep(20);
> + }
> +}
> +EXPORT_SYMBOL(blk_mq_tagset_wait_request_completed);
