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From:   Daniel Vetter <daniel@ffwll.ch>
Date:   Mon, 7 Nov 2022 18:25:50 +0100
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Subject: Re: [PATCH v7 18/21] dma-buf: Move dma_buf_mmap() to dynamic locking specification
To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>
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On Mon, 17 Oct 2022 at 19:25, Dmitry Osipenko
<dmitry.osipenko@collabora.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@linaro.org>
> Acked-by: Christian K=C3=B6nig <christian.koenig@amd.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.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_BU=
F);
>  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 =3D pgoff;
>
> -       return dmabuf->ops->mmap(dmabuf, vma);
> +       dma_resv_lock(dmabuf->resv, NULL);
> +       ret =3D dmabuf->ops->mmap(dmabuf, vma);
> +       dma_resv_unlock(dmabuf->resv);
> +
> +       return ret;
>  }
>  EXPORT_SYMBOL_NS_GPL(dma_buf_mmap, DMA_BUF);
>
> --
> 2.37.3
>


--=20
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch