linux-kernel - Re: [REGRESSION] Recent swiotlb DMA_FROM

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Message-ID: <CAHk-=wgqHqb_yaNUGwMfLJJw28VvauSB6sSMCi3Bu7Q0-N0GEQ@mail.gmail.com>
Date:   Sat, 26 Mar 2022 15:41:40 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     Toke Høiland-Jørgensen <toke@...e.dk>,
        Halil Pasic <pasic@...ux.ibm.com>,
        Robin Murphy <robin.murphy@....com>,
        Maxime Bizon <mbizon@...ebox.fr>,
        Netdev <netdev@...r.kernel.org>, Kalle Valo <kvalo@...nel.org>,
        linux-wireless <linux-wireless@...r.kernel.org>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        stable <stable@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        iommu <iommu@...ts.linux-foundation.org>,
        Olha Cherevyk <olha.cherevyk@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break
 ath9k-based AP

On Sat, Mar 26, 2022 at 3:38 PM David Laight <David.Laight@...lab.com> wrote:
>
> Is the idea of 'buffer ownership' even a good one?

I do think it might be best to not think in those terms, but literally
just in data movement terms.

Because the "buffer ownership" mental model is clearly confused, when
data transfer might be ongoing, but the CPU might need to just look at
"what's going on right now" without actually taking any ownership of
the buffer.

                Linus