linux-kernel - Re: [PATCH v11 3/3] scsi: set max_bio

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Date:   Wed, 2 Jun 2021 12:04:04 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Changheun Lee <nanich.lee@...sung.com>, hch@...radead.org,
        Johannes.Thumshirn@....com, alex_y_xu@...oo.ca,
        asml.silence@...il.com, axboe@...nel.dk, bgoncalv@...hat.com,
        damien.lemoal@....com, gregkh@...uxfoundation.org,
        jaegeuk@...nel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, ming.lei@...hat.com, osandov@...com,
        patchwork-bot@...nel.org, tj@...nel.org, tom.leiming@...il.com,
        yi.zhang@...hat.com
Cc:     jisoo2146.oh@...sung.com, junho89.kim@...sung.com,
        mj0123.lee@...sung.com, seunghwan.hyun@...sung.com,
        sookwan7.kim@...sung.com, woosung2.lee@...sung.com,
        yt0928.kim@...sung.com
Subject: Re: [PATCH v11 3/3] scsi: set max_bio_bytes with queue max sectors

On 6/2/21 5:10 AM, Changheun Lee wrote:
> Set max_bio_bytes same with queue max sectors. It will lead to fast bio
> submit when bio size is over than queue max sectors. And it might be helpful
> to align submit bio size in some case.
> 
> Signed-off-by: Changheun Lee <nanich.lee@...sung.com>
> ---
>  drivers/scsi/scsi_lib.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 532304d42f00..f6269268b0e0 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1837,6 +1837,8 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q)
>  	blk_queue_virt_boundary(q, shost->virt_boundary_mask);
>  	dma_set_max_seg_size(dev, queue_max_segment_size(q));
>  
> +	blk_queue_max_bio_bytes(q, queue_max_sectors(q));
> +
>  	/*
>  	 * Set a reasonable default alignment:  The larger of 32-byte (dword),
>  	 * which is a common minimum for HBAs, and the minimum DMA alignment,

Has this patch been tested with dm-crypt on top of a SCSI device? I'm
concerned that this patch will trigger data corruption with dm-crypt on
top because the above change will make the following dm-crypt code fail
for a sufficiently large bio:

		bio_add_page(clone, page, len, 0);

When testing dm-crypt on top of this patch series, please change the
above dm-crypt code into the following before running any tests:

		WARN_ON(bio_add_page(clone, page, len, 0) < len);

Thanks,

Bart.