linux-kernel - Re: [PATCH v7 18/21] dma-buf: Move dma_buf_mmap() to dynamic locking specification

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Message-ID: <CAKMK7uFFwTfNYT2BrubYvUMrH4fEmtF=yJshUck3-gKYLGqxCg@mail.gmail.com>
Date:   Mon, 7 Nov 2022 18:25:50 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc:     David Airlie <airlied@...ux.ie>, Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>,
        Daniel Almeida <daniel.almeida@...labora.com>,
        Gert Wollny <gert.wollny@...labora.com>,
        Gustavo Padovan <gustavo.padovan@...labora.com>,
        Daniel Stone <daniel@...ishbar.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Rob Clark <robdclark@...il.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Christian König <christian.koenig@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        Thierry Reding <thierry.reding@...il.com>,
        Tomasz Figa <tfiga@...omium.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
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        Jani Nikula <jani.nikula@...ux.intel.com>,
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        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
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Subject: Re: [PATCH v7 18/21] dma-buf: Move dma_buf_mmap() to dynamic locking specification

On Mon, 17 Oct 2022 at 19:25, Dmitry Osipenko
<dmitry.osipenko@...labora.com> wrote:
>
> Move dma_buf_mmap() function to the dynamic locking specification by
> taking the reservation lock. Neither of the today's drivers take the
> reservation lock within the mmap() callback, hence it's safe to enforce
> the locking.
>
> Acked-by: Sumit Semwal <sumit.semwal@...aro.org>
> Acked-by: Christian König <christian.koenig@....com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>

Just noticed this while reading code ... this patch seems to have
missed dma_buf_mmap_internal()?

Might be good if at least some drivers gain a dma_resv_assert_held in
that path to make sure we're not quite this bad, together with fixing
this issue.
-Daniel

> ---
>  drivers/dma-buf/dma-buf.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index f54c649f922a..f149b384f4dd 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -1390,6 +1390,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF);
>  int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>                  unsigned long pgoff)
>  {
> +       int ret;
> +
>         if (WARN_ON(!dmabuf || !vma))
>                 return -EINVAL;
>
> @@ -1410,7 +1412,11 @@ int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>         vma_set_file(vma, dmabuf->file);
>         vma->vm_pgoff = pgoff;
>
> -       return dmabuf->ops->mmap(dmabuf, vma);
> +       dma_resv_lock(dmabuf->resv, NULL);
> +       ret = dmabuf->ops->mmap(dmabuf, vma);
> +       dma_resv_unlock(dmabuf->resv);
> +
> +       return ret;
>  }
>  EXPORT_SYMBOL_NS_GPL(dma_buf_mmap, DMA_BUF);
>
> --
> 2.37.3
>


-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch