linux-kernel - Re: [PATCH] nvme-pci: add missing condition check for existence of mapped data

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Message-ID: <20240730173920.GD4209@unreal>
Date: Tue, 30 Jul 2024 20:39:20 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Christoph Hellwig <hch@....de>
Cc: Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Sagi Grimberg <sagi@...mberg.me>,
	Chaitanya Kulkarni <chaitanya.kulkarni@....com>,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] nvme-pci: add missing condition check for existence of
 mapped data

On Tue, Jul 30, 2024 at 07:21:11PM +0200, Christoph Hellwig wrote:
> On Tue, Jul 30, 2024 at 11:09:04AM -0600, Keith Busch wrote:
> > > +	if (blk_rq_nr_phys_segments(req))
> > > +		nvme_unmap_data(dev, req);
> > 
> > This is already applied, but it is kind of strange. We get here only if
> > metadata mapping fails. Is there actually a command that has metadata
> > without data?
> 
> Well, passthrough can always set metadata to map without data even
> if there is no NVMe defined command that works that way, so we should
> handle the error.
> 
> But I suspect this is due to Leon's dma-mapping work, and it probably
> points to a bug in that :)

Yeah, something like that. I had a bug in my code and saw this
asymmetry while reviewed all paths which lead to nvme_unmap_data().

Thanks