linux-kernel - Re: [PATCH v2 2/4] dma-buf: enable signaling for the stub fence on debug

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Message-ID: <37ec6f1d-a3f4-6fa3-6d5c-fe89bb958d87@amd.com>
Date:   Tue, 6 Sep 2022 09:09:46 +0200
From:   Christian König <christian.koenig@....com>
To:     Arvind Yadav <Arvind.Yadav@....com>, andrey.grodzovsky@....com,
        shashank.sharma@....com, amaranath.somalapuram@....com,
        Arunpravin.PaneerSelvam@....com, sumit.semwal@...aro.org,
        gustavo@...ovan.org, airlied@...ux.ie, daniel@...ll.ch,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] dma-buf: enable signaling for the stub fence on
 debug



Am 05.09.22 um 18:35 schrieb Arvind Yadav:
> Here's on debug enabling software signaling for the stub fence
> which is always signaled. This fence should enable software
> signaling otherwise the AMD GPU scheduler will cause a GPU reset
> due to a GPU scheduler cleanup activity timeout.
>
> Signed-off-by: Arvind Yadav <Arvind.Yadav@....com>
> ---
>
> Changes in v1 :
> 1- Addressing Christian's comment to remove unnecessary callback.
> 2- Replacing CONFIG_DEBUG_WW_MUTEX_SLOWPATH instead of CONFIG_DEBUG_FS.
> 3- The version of this patch is also changed and previously
> it was [PATCH 3/4]
>
> ---
>   drivers/dma-buf/dma-fence.c | 7 +++++++
>   1 file changed, 7 insertions(+)
>
> diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> index 066400ed8841..2378b12538c4 100644
> --- a/drivers/dma-buf/dma-fence.c
> +++ b/drivers/dma-buf/dma-fence.c
> @@ -27,6 +27,10 @@ EXPORT_TRACEPOINT_SYMBOL(dma_fence_signaled);
>   static DEFINE_SPINLOCK(dma_fence_stub_lock);
>   static struct dma_fence dma_fence_stub;
>   
> +#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
> +static bool __dma_fence_enable_signaling(struct dma_fence *fence);
> +#endif
> +

I would rename the function to something like 
dma_fence_enable_signaling_locked().

And please don't add any #ifdef if it isn't absolutely necessary. This 
makes the code pretty fragile.

>   /*
>    * fence context counter: each execution context should have its own
>    * fence context, this allows checking if fences belong to the same
> @@ -136,6 +140,9 @@ struct dma_fence *dma_fence_get_stub(void)
>   			       &dma_fence_stub_ops,
>   			       &dma_fence_stub_lock,
>   			       0, 0);
> +#ifdef CONFIG_DEBUG_WW_MUTEX_SLOWPATH
> +		__dma_fence_enable_signaling(&dma_fence_stub);
> +#endif

Alternatively in this particular case you could just set the bit 
manually here since this is part of the dma_fence code anyway.

Christian.

>   		dma_fence_signal_locked(&dma_fence_stub);
>   	}
>   	spin_unlock(&dma_fence_stub_lock);