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Date:   Thu, 1 Sep 2022 09:07:00 +0200
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Subject: Re: [PATCH v4 16/21] dma-buf: Move dma_buf_attach() to dynamic
 locking specification
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To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>,
        David Airlie <airlied@linux.ie>,
        Gerd Hoffmann <kraxel@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
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        Gert Wollny <gert.wollny@collabora.com>,
        Gustavo Padovan <gustavo.padovan@collabora.com>,
        Daniel Stone <daniel@fooishbar.org>,
        Tomeu Vizoso <tomeu.vizoso@collabora.com>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Rob Clark <robdclark@gmail.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Tomasz Figa <tfiga@chromium.org>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Jani Nikula <jani.nikula@linux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
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        Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>,
        =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= <thomas_os@shipmail.org>,
        Qiang Yu <yuq825@gmail.com>,
        Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
        Amol Maheshwari <amahesh@qti.qualcomm.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Leon Romanovsky <leon@kernel.org>,
        Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>,
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        Christian Gmeiner <christian.gmeiner@gmail.com>
Cc:     dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        Dmitry Osipenko <digetx@gmail.com>,
        linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org,
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        kernel@collabora.com, virtualization@lists.linux-foundation.org,
        linux-rdma@vger.kernel.org, linux-arm-msm@vger.kernel.org
References: <20220831153757.97381-1-dmitry.osipenko@collabora.com>
 <20220831153757.97381-17-dmitry.osipenko@collabora.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
In-Reply-To: <20220831153757.97381-17-dmitry.osipenko@collabora.com>
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Am 31.08.22 um 17:37 schrieb Dmitry Osipenko:
> Move dma-buf attachment API functions to the dynamic locking specification
> by taking the reservation lock around the mapping operations. The strict
> locking convention prevents deadlock situations for dma-buf importers and
> exporters.
>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>

Reviewed-by: Christian König <christian.koenig@amd.com>

> ---
>   drivers/dma-buf/dma-buf.c | 20 ++++++++------------
>   1 file changed, 8 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index ceea4839c641..073942bf5ae9 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -858,8 +858,8 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>   	    dma_buf_is_dynamic(dmabuf)) {
>   		struct sg_table *sgt;
>   
> +		dma_resv_lock(attach->dmabuf->resv, NULL);
>   		if (dma_buf_is_dynamic(attach->dmabuf)) {
> -			dma_resv_lock(attach->dmabuf->resv, NULL);
>   			ret = dmabuf->ops->pin(attach);
>   			if (ret)
>   				goto err_unlock;
> @@ -872,8 +872,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>   			ret = PTR_ERR(sgt);
>   			goto err_unpin;
>   		}
> -		if (dma_buf_is_dynamic(attach->dmabuf))
> -			dma_resv_unlock(attach->dmabuf->resv);
> +		dma_resv_unlock(attach->dmabuf->resv);
>   		attach->sgt = sgt;
>   		attach->dir = DMA_BIDIRECTIONAL;
>   	}
> @@ -889,8 +888,7 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>   		dmabuf->ops->unpin(attach);
>   
>   err_unlock:
> -	if (dma_buf_is_dynamic(attach->dmabuf))
> -		dma_resv_unlock(attach->dmabuf->resv);
> +	dma_resv_unlock(attach->dmabuf->resv);
>   
>   	dma_buf_detach(dmabuf, attach);
>   	return ERR_PTR(ret);
> @@ -936,21 +934,19 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>   	if (WARN_ON(!dmabuf || !attach))
>   		return;
>   
> +	dma_resv_lock(attach->dmabuf->resv, NULL);
> +
>   	if (attach->sgt) {
> -		if (dma_buf_is_dynamic(attach->dmabuf))
> -			dma_resv_lock(attach->dmabuf->resv, NULL);
>   
>   		__unmap_dma_buf(attach, attach->sgt, attach->dir);
>   
> -		if (dma_buf_is_dynamic(attach->dmabuf)) {
> +		if (dma_buf_is_dynamic(attach->dmabuf))
>   			dmabuf->ops->unpin(attach);
> -			dma_resv_unlock(attach->dmabuf->resv);
> -		}
>   	}
> -
> -	dma_resv_lock(dmabuf->resv, NULL);
>   	list_del(&attach->node);
> +
>   	dma_resv_unlock(dmabuf->resv);
> +
>   	if (dmabuf->ops->detach)
>   		dmabuf->ops->detach(dmabuf, attach);
>