linux-kernel - Re: [RFC 02/17] dma-fence: basic lockdep annotations

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Date:   Tue, 12 May 2020 09:09:52 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daniel Vetter <daniel.vetter@...ll.ch>
Cc:     DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-rdma@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Christian König <christian.koenig@....com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [RFC 02/17] dma-fence: basic lockdep annotations

On Tue, May 12, 2020 at 10:59:29AM +0200, Daniel Vetter wrote:
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 6802125349fb..d5c0fd2efc70 100644
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -110,6 +110,52 @@ u64 dma_fence_context_alloc(unsigned num)
>  }
>  EXPORT_SYMBOL(dma_fence_context_alloc);
>  
> +#ifdef CONFIG_LOCKDEP
> +struct lockdep_map	dma_fence_lockdep_map = {
> +	.name = "dma_fence_map"
> +};
> +
> +bool dma_fence_begin_signalling(void)
> +{

Why is this global? I would have expected it to be connected to a
single fence?

It would also be alot nicer if this was some general lockdep feature,
not tied to dmabuf. This exact problem also strikes anyone using
completions, for instance, and the same solution should be
applicable??

Jason