linux-kernel - Re: [PATCH 4/4] nvmet-fc: Use new SGL alloc/free helper for requests

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Message-ID: <aef7b203-a16b-738f-4ca2-d50768d70ca0@broadcom.com>
Date:   Thu, 29 Mar 2018 10:39:48 -0700
From:   James Smart <james.smart@...adcom.com>
To:     Logan Gunthorpe <logang@...tatee.com>,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org
Cc:     Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH 4/4] nvmet-fc: Use new SGL alloc/free helper for requests

On 3/29/2018 10:02 AM, Logan Gunthorpe wrote:
> Per the bug in the previous patch, I don't think that was ever a valid
> assumption. It doesn't have anything to do with the sgl_alloc change
> either. The dma_map interface is allowed to merge SGLs and that's why it
> can return fewer nents than it was passed. I'm not sure how many or
> which DMA ops actually do this which is why it hasn't actually
> manifested itself as a bug; but it is part of how the interface is
> specified to work.

Argh.. yep. I'll have to correct that assumption. The bug would have 
only shown up on i/o sizes beyond a particular length.

>
> I think we need to store the sg_map_cnt separately and use it instead of
> the calculation based on the transfer length. But this is really a fix
> that should be rolled in with the previous patch. If you can point me to
> where this needs to change I can update my patch, or if you want to fix
> it yourself go ahead.
I'll fix it as it's part of the assumption fix.

With the nulling/zeroing, I'm good with your patch.

-- james.