linux-kernel - Re: [PATCH v3 15/15] nvme: Ensure atomic writes will be executed atomically

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Message-ID: <ZbGwv4uFdJyfKtk5@kbusch-mbp.dhcp.thefacebook.com>
Date: Wed, 24 Jan 2024 17:52:15 -0700
From: Keith Busch <kbusch@...nel.org>
To: John Garry <john.g.garry@...cle.com>
Cc: axboe@...nel.dk, hch@....de, sagi@...mberg.me, jejb@...ux.ibm.com,
	martin.petersen@...cle.com, djwong@...nel.org,
	viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com,
	jack@...e.cz, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tytso@....edu, jbongio@...gle.com, linux-scsi@...r.kernel.org,
	ming.lei@...hat.com, ojaswin@...ux.ibm.com, bvanassche@....org,
	Alan Adamson <alan.adamson@...cle.com>
Subject: Re: [PATCH v3 15/15] nvme: Ensure atomic writes will be executed
 atomically

On Wed, Jan 24, 2024 at 11:38:41AM +0000, John Garry wrote:
> diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
> index 5045c84f2516..6a34a5d92088 100644
> --- a/drivers/nvme/host/core.c
> +++ b/drivers/nvme/host/core.c
> @@ -911,6 +911,32 @@ static inline blk_status_t nvme_setup_rw(struct nvme_ns *ns,
>  	if (req->cmd_flags & REQ_RAHEAD)
>  		dsmgmt |= NVME_RW_DSM_FREQ_PREFETCH;
>  
> +	/*
> +	 * Ensure that nothing has been sent which cannot be executed
> +	 * atomically.
> +	 */
> +	if (req->cmd_flags & REQ_ATOMIC) {
> +		struct nvme_ns_head *head = ns->head;
> +		u32 boundary_bytes = head->atomic_boundary;
> +
> +		if (blk_rq_bytes(req) > ns->head->atomic_max)
> +			return BLK_STS_IOERR;
> +
> +		if (boundary_bytes) {
> +			u32 mask = boundary_bytes - 1, imask = ~mask;
> +			u32 start = blk_rq_pos(req) << SECTOR_SHIFT;
> +			u32 end = start + blk_rq_bytes(req);
> +
> +			if (blk_rq_bytes(req) > boundary_bytes)
> +				return BLK_STS_IOERR;
> +
> +			if (((start & imask) != (end & imask)) &&
> +			    (end & mask)) {
> +				return BLK_STS_IOERR;
> +			}
> +		}
> +	}

Aren't these new fields, atomic_max and atomic_boundary, duplicates of
the equivalent queue limits? Let's just use the queue limits instead.

And couldn't we generically validate the constraints are not violated in
submit_bio_noacct() instead of doing that in the low level driver? The
driver assumes all other requests are already sanity checked, so I don't
think we should change the responsibility for that just for this flag.