Re: [PATCH] drm/panfrost: fix reference leak in panfrost_job_hw_submit

[Steven Price]

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@xxxxxxxxxx>
> Signed-off-by: Qinglang Miao <miaoqinglang@xxxxxxxxxx>
> ---
>   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;
>