linux-kernel - Re: [PATCH v3] Add udmabuf misc device

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Date:   Tue, 29 May 2018 10:48:45 +0200
From:   Gerd Hoffmann <kraxel@...hat.com>
To:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Shuah Khan <shuah@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DMA BUFFER SHARING FRAMEWORK" 
        <linux-media@...r.kernel.org>,
        "moderated list:DMA BUFFER SHARING FRAMEWORK" 
        <linaro-mm-sig@...ts.linaro.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>
Subject: Re: [PATCH v3] Add udmabuf misc device

  Hi,

> > +static void *kmap_atomic_udmabuf(struct dma_buf *buf, unsigned long page_num)
> > +{
> > +	struct udmabuf *ubuf = buf->priv;
> > +	struct page *page = ubuf->pages[page_num];
> > +
> > +	return kmap_atomic(page);
> > +}
> > +
> > +static void *kmap_udmabuf(struct dma_buf *buf, unsigned long page_num)
> > +{
> > +	struct udmabuf *ubuf = buf->priv;
> > +	struct page *page = ubuf->pages[page_num];
> > +
> > +	return kmap(page);
> > +}
> 
> The above leaks like mad since no kunamp?

/me checks code.  Oops.  Yes.

The docs say map() is required and unmap() is not (for both atomic and
non-atomic cases), so I assumed there is a default implementation just
doing kunmap(page).  Which is not the case.  /me looks a bit surprised.

I'll fix it for v4.

> Also I think we have 0 users of the kmap atomic interfaces ... so not sure
> whether it's worth it to implement those.

Well, the docs are correct.  kmap_atomic() is required, dma-buf.c calls
the function pointer without checking it exists beforehand ...

cheers,
  Gerd