linux-kernel - Re: [RFC PATCH 3/3] nvme: Introduce nvme_execute_passthru_rq

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Message-ID: <20191027150937.GC5843@lst.de>
Date:   Sun, 27 Oct 2019 16:09:37 +0100
From:   Christoph Hellwig <hch@....de>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <kbusch@...nel.org>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>,
        Max Gurtovoy <maxg@...lanox.com>,
        Stephen Bates <sbates@...thlin.com>
Subject: Re: [RFC PATCH 3/3] nvme: Introduce
 nvme_execute_passthru_rq_nowait()

On Fri, Oct 25, 2019 at 02:25:35PM -0600, Logan Gunthorpe wrote:
> This function is similar to nvme_execute_passthru_rq() but does
> not wait and will call a callback when the request is complete.
> 
> The new function can also be called in interrupt context, so if there
> are side effects, the request will be executed in a work queue to
> avoid sleeping.

Why would you ever call it from interrupt context?  All the target
submission handlers should run in process context.

> +void nvme_execute_passthru_rq_nowait(struct request *rq, rq_end_io_fn *done)
> +{
> +	struct nvme_command *cmd = nvme_req(rq)->cmd;
> +	struct nvme_ctrl *ctrl = nvme_req(rq)->ctrl;
> +	struct nvme_ns *ns = rq->q->queuedata;
> +	struct gendisk *disk = ns ? ns->disk : NULL;
> +	u32 effects;
> +
> +	/*
> +	 * This function may be called in interrupt context, so we cannot sleep
> +	 * but nvme_passthru_[start|end]() may sleep so we need to execute
> +	 * the command in a work queue.
> +	 */
> +	effects = nvme_command_effects(ctrl, ns, cmd->common.opcode);
> +	if (effects) {
> +		rq->end_io = done;
> +		INIT_WORK(&nvme_req(rq)->work, nvme_execute_passthru_rq_work);
> +		queue_work(nvme_wq, &nvme_req(rq)->work);

But independent of the target code - I'd much rather leave this to the
caller.  Just call nvme_command_effects in the target code, then if
there are not side effects use blk_execute_rq_nowait directly, else
schedule a workqueue in the target code and call
nvme_execute_passthru_rq from it.