linux-kernel - Re: [PATCH v3 5/9] dma-buf: Move dma_buf_mmap_unlocked() to dynamic locking specification

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Date:   Wed, 24 Aug 2022 16:01:06 +0200
From:   Christian König <christian.koenig@....com>
To:     Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Gurchetan Singh <gurchetansingh@...omium.org>,
        Chia-I Wu <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        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>,
        "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>,
        Alex Deucher <alexander.deucher@....com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Thomas Hellström <thomas_os@...pmail.org>,
        Qiang Yu <yuq825@...il.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org,
        amd-gfx@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org,
        linux-rdma@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        lima@...ts.freedesktop.org
Subject: Re: [PATCH v3 5/9] dma-buf: Move dma_buf_mmap_unlocked() to dynamic
 locking specification

This should work, but I'm really wondering if this makes a difference 
for somebody.

Anyway the approach is fine with me: Acked-by: Christian König 
<christian.koenig@....com>

Regards,
Christian.

Am 24.08.22 um 12:22 schrieb Dmitry Osipenko:
> Move dma_buf_mmap_unlocked() 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.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---
>   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 f358af401360..4556a12bd741 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -1348,6 +1348,8 @@ EXPORT_SYMBOL_NS_GPL(dma_buf_end_cpu_access, DMA_BUF);
>   int dma_buf_mmap_unlocked(struct dma_buf *dmabuf, struct vm_area_struct *vma,
>   			  unsigned long pgoff)
>   {
> +	int ret;
> +
>   	if (WARN_ON(!dmabuf || !vma))
>   		return -EINVAL;
>   
> @@ -1368,7 +1370,11 @@ int dma_buf_mmap_unlocked(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_unlocked, DMA_BUF);
>