Re: [PATCH V3 2/4] blk-mq: implement queue quiesce via percpu_ref for BLK_MQ_F_BLOCKING

Keith Busch
2020-09-08T20:01:04Z

On Tue, Sep 08, 2020 at 04:15:36PM +0800, Ming Lei wrote:
> void blk_mq_quiesce_queue(struct request_queue *q)
> {
> - struct blk_mq_hw_ctx *hctx;
> - unsigned int i;
> - bool rcu = false;
> + bool blocking = !!(q->tag_set->flags & BLK_MQ_F_BLOCKING);
>
> mutex_lock(&q->mq_quiesce_lock);
>
> - if (blk_queue_quiesced(q))
> - goto exit;

Why remove the 'goto exit' on this condition? There shouldn't be a need
to synchronize dispatch again if a previous quiesce already did so.

> - blk_mq_quiesce_queue_nowait(q);
> -
> - queue_for_each_hw_ctx(q, hctx, i) {
> - if (hctx->flags & BLK_MQ_F_BLOCKING)
> - synchronize_srcu(hctx->srcu);
> - else
> - rcu = true;
> + if (!blk_queue_quiesced(q)) {
> + blk_mq_quiesce_queue_nowait(q);
> + if (blocking)
> + percpu_ref_kill(&q->dispatch_counter);
> }
> - if (rcu)
> +
> + if (blocking)
> + wait_event(q->mq_quiesce_wq,
> + percpu_ref_is_zero(&q->dispatch_counter));
> + else
> synchronize_rcu();
> - exit:
> +
> mutex_unlock(&q->mq_quiesce_lock);
> }