linux-kernel - Re: [PATCH v2] drm/etnaviv: fix ref count leak via pm_runtime_get

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Message-ID: <befc07e1d630dbc5a6f96fba4e47e083e6386090.camel@pengutronix.de>
Date:   Wed, 17 Jun 2020 11:53:08 +0200
From:   Lucas Stach <l.stach@...gutronix.de>
To:     Navid Emamdoost <navid.emamdoost@...il.com>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, etnaviv@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     kjlu@....edu, mccamant@...umn.edu, andy.shevchenko@...il.com,
        emamd001@....edu, wu000273@....edu
Subject: Re: [PATCH v2] drm/etnaviv: fix ref count leak via
 pm_runtime_get_sync

Hi Navid,

Am Montag, den 15.06.2020, 01:12 -0500 schrieb Navid Emamdoost:
> in etnaviv_gpu_submit, etnaviv_gpu_recover_hang, etnaviv_gpu_debugfs,
> and etnaviv_gpu_init the call to pm_runtime_get_sync increments the
> counter even in case of failure, leading to incorrect ref count.
> In case of failure, decrement the ref count before returning.

While that change is correct with the current API, may I ask the
question why the way this API works is considered reasonable? A API
call that fails, but still changes internal state and expects the
caller to clean up the mess it not really what I would consider fool-
proof API design. Is there a specific reason why it is done this way
and not handled internally?

Regards,
Lucas

> Signed-off-by: Navid Emamdoost <navid.emamdoost@...il.com>
> ---
> Changes in v2:
> 	- replace pm_runtime_put with  pm_runtime_put_noidle
> ---
>  drivers/gpu/drm/etnaviv/etnaviv_gpu.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> index a31eeff2b297..7c9f3f9ba123 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gpu.c
> @@ -722,7 +722,7 @@ int etnaviv_gpu_init(struct etnaviv_gpu *gpu)
>  	ret = pm_runtime_get_sync(gpu->dev);
>  	if (ret < 0) {
>  		dev_err(gpu->dev, "Failed to enable GPU power domain\n");
> -		return ret;
> +		goto pm_put;
>  	}
>  
>  	etnaviv_hw_identify(gpu);
> @@ -819,6 +819,7 @@ int etnaviv_gpu_init(struct etnaviv_gpu *gpu)
>  
>  fail:
>  	pm_runtime_mark_last_busy(gpu->dev);
> +pm_put:
>  	pm_runtime_put_autosuspend(gpu->dev);
>  
>  	return ret;
> @@ -859,7 +860,7 @@ int etnaviv_gpu_debugfs(struct etnaviv_gpu *gpu, struct seq_file *m)
>  
>  	ret = pm_runtime_get_sync(gpu->dev);
>  	if (ret < 0)
> -		return ret;
> +		goto pm_put;
>  
>  	dma_lo = gpu_read(gpu, VIVS_FE_DMA_LOW);
>  	dma_hi = gpu_read(gpu, VIVS_FE_DMA_HIGH);
> @@ -1003,6 +1004,7 @@ int etnaviv_gpu_debugfs(struct etnaviv_gpu *gpu, struct seq_file *m)
>  	ret = 0;
>  
>  	pm_runtime_mark_last_busy(gpu->dev);
> +pm_put:
>  	pm_runtime_put_autosuspend(gpu->dev);
>  
>  	return ret;
> @@ -1016,7 +1018,7 @@ void etnaviv_gpu_recover_hang(struct etnaviv_gpu *gpu)
>  	dev_err(gpu->dev, "recover hung GPU!\n");
>  
>  	if (pm_runtime_get_sync(gpu->dev) < 0)
> -		return;
> +		goto pm_put;
>  
>  	mutex_lock(&gpu->lock);
>  
> @@ -1035,6 +1037,7 @@ void etnaviv_gpu_recover_hang(struct etnaviv_gpu *gpu)
>  
>  	mutex_unlock(&gpu->lock);
>  	pm_runtime_mark_last_busy(gpu->dev);
> +pm_put:
>  	pm_runtime_put_autosuspend(gpu->dev);
>  }
>  
> @@ -1308,8 +1311,10 @@ struct dma_fence *etnaviv_gpu_submit(struct etnaviv_gem_submit *submit)
>  
>  	if (!submit->runtime_resumed) {
>  		ret = pm_runtime_get_sync(gpu->dev);
> -		if (ret < 0)
> +		if (ret < 0) {
> +			pm_runtime_put_noidle(gpu->dev);
>  			return NULL;
> +		}
>  		submit->runtime_resumed = true;
>  	}
>  
> @@ -1326,6 +1331,7 @@ struct dma_fence *etnaviv_gpu_submit(struct etnaviv_gem_submit *submit)
>  	ret = event_alloc(gpu, nr_events, event);
>  	if (ret) {
>  		DRM_ERROR("no free events\n");
> +		pm_runtime_put_noidle(gpu->dev);
>  		return NULL;
>  	}
>