linux-kernel - Re: [PATCH] drm/panfrost: fix reference leak in panfrost_job_hw

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Message-ID: <46d1944e-fbbe-075f-1c5b-356b5ce73ee0@arm.com>
Date:   Fri, 27 Nov 2020 10:06:11 +0000
From:   Steven Price <steven.price@....com>
To:     Qinglang Miao <miaoqinglang@...wei.com>,
        Rob Herring <robh@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Alyssa Rosenzweig <alyssa.rosenzweig@...labora.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/panfrost: fix reference leak in
 panfrost_job_hw_submit

On 27/11/2020 09:44, Qinglang Miao wrote:
> pm_runtime_get_sync will increment pm usage counter even it
> failed. Forgetting to putting operation will result in a
> reference leak here.
> 
> A new function pm_runtime_resume_and_get is introduced in
> [0] to keep usage counter balanced. So We fix the reference
> leak by replacing it with new funtion.
> 
> [0] dd8088d5a896 ("PM: runtime: Add  pm_runtime_resume_and_get to deal with usage counter")
> 
> Fixes: f3ba91228e8e ("drm/panfrost: Add initial panfrost driver")
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Qinglang Miao <miaoqinglang@...wei.com>
> ---
>   drivers/gpu/drm/panfrost/panfrost_job.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panfrost/panfrost_job.c b/drivers/gpu/drm/panfrost/panfrost_job.c
> index 30e7b7196..04cf3bb67 100644
> --- a/drivers/gpu/drm/panfrost/panfrost_job.c
> +++ b/drivers/gpu/drm/panfrost/panfrost_job.c
> @@ -147,7 +147,7 @@ static void panfrost_job_hw_submit(struct panfrost_job *job, int js)
>   
>   	panfrost_devfreq_record_busy(&pfdev->pfdevfreq);
>   
> -	ret = pm_runtime_get_sync(pfdev->dev);
> +	ret = pm_runtime_resume_and_get(pfdev->dev);

Sorry, but in this case this change isn't correct. 
panfrost_job_hw_submit() is expected to be unbalanced (the PM reference 
count is expected to be incremented on return).

In the case where pm_runtime_get_sync() fails, the job will eventually 
timeout, and there's a corresponding pm_runtime_put_noidle() in 
panfrost_reset().

Potentially this could be handled better (e.g. without waiting for the 
timeout to occur), but equally this isn't something we expect to happen 
in normal operation).

Steve

>   	if (ret < 0)
>   		return;
>   
>