linux-kernel - Re: [PATCH] Revert "drm/msm/gpu: Push gpu lock down past runpm"

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Message-ID: <ZZ52YNc-TkeG7PZO@phenom.ffwll.local>
Date: Wed, 10 Jan 2024 11:50:08 +0100
From: Daniel Vetter <daniel@...ll.ch>
To: Rob Clark <robdclark@...il.com>
Cc: dri-devel@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
	freedreno@...ts.freedesktop.org, Rob Clark <robdclark@...omium.org>,
	Abhinav Kumar <quic_abhinavk@...cinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Revert "drm/msm/gpu: Push gpu lock down past runpm"

On Tue, Jan 09, 2024 at 10:22:17AM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@...omium.org>
> 
> This reverts commit abe2023b4cea192ab266b351fd38dc9dbd846df0.
> 
> Changing the locking order means that scheduler/msm_job_run() can race
> with the recovery kthread worker, with the result that the GPU gets an
> extra runpm get when we are trying to power it off.  Leaving the GPU in
> an unrecovered state.

The recovery kthread is supposed to stop all the relevant schedulers,
which should remove any possible race conditions. So unless there's more
going on, or you have your own recovery kthread (don't, reuse the one from
the scheduler with your own work items, that's why you can provide that)
this looks like an incomplete/incorrect explanation ... ?

Slightly confused
-Sima

> 
> I'll need to come up with a different scheme for appeasing lockdep.
> 
> Signed-off-by: Rob Clark <robdclark@...omium.org>
> ---
>  drivers/gpu/drm/msm/msm_gpu.c        | 11 +++++------
>  drivers/gpu/drm/msm/msm_ringbuffer.c |  7 +++++--
>  2 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/msm_gpu.c b/drivers/gpu/drm/msm/msm_gpu.c
> index 095390774f22..655002b21b0d 100644
> --- a/drivers/gpu/drm/msm/msm_gpu.c
> +++ b/drivers/gpu/drm/msm/msm_gpu.c
> @@ -751,12 +751,14 @@ void msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
>  	struct msm_ringbuffer *ring = submit->ring;
>  	unsigned long flags;
>  
> -	pm_runtime_get_sync(&gpu->pdev->dev);
> +	WARN_ON(!mutex_is_locked(&gpu->lock));
>  
> -	mutex_lock(&gpu->lock);
> +	pm_runtime_get_sync(&gpu->pdev->dev);
>  
>  	msm_gpu_hw_init(gpu);
>  
> +	submit->seqno = submit->hw_fence->seqno;
> +
>  	update_sw_cntrs(gpu);
>  
>  	/*
> @@ -781,11 +783,8 @@ void msm_gpu_submit(struct msm_gpu *gpu, struct msm_gem_submit *submit)
>  	gpu->funcs->submit(gpu, submit);
>  	gpu->cur_ctx_seqno = submit->queue->ctx->seqno;
>  
> -	hangcheck_timer_reset(gpu);
> -
> -	mutex_unlock(&gpu->lock);
> -
>  	pm_runtime_put(&gpu->pdev->dev);
> +	hangcheck_timer_reset(gpu);
>  }
>  
>  /*
> diff --git a/drivers/gpu/drm/msm/msm_ringbuffer.c b/drivers/gpu/drm/msm/msm_ringbuffer.c
> index e0ed27739449..548f5266a7d3 100644
> --- a/drivers/gpu/drm/msm/msm_ringbuffer.c
> +++ b/drivers/gpu/drm/msm/msm_ringbuffer.c
> @@ -21,8 +21,6 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
>  
>  	msm_fence_init(submit->hw_fence, fctx);
>  
> -	submit->seqno = submit->hw_fence->seqno;
> -
>  	mutex_lock(&priv->lru.lock);
>  
>  	for (i = 0; i < submit->nr_bos; i++) {
> @@ -35,8 +33,13 @@ static struct dma_fence *msm_job_run(struct drm_sched_job *job)
>  
>  	mutex_unlock(&priv->lru.lock);
>  
> +	/* TODO move submit path over to using a per-ring lock.. */
> +	mutex_lock(&gpu->lock);
> +
>  	msm_gpu_submit(gpu, submit);
>  
> +	mutex_unlock(&gpu->lock);
> +
>  	return dma_fence_get(submit->hw_fence);
>  }
>  
> -- 
> 2.43.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch