linux-kernel - Re: [PATCH] drm/vc4: Fix refcounting of runtime PM get if it errors out.

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Message-ID: <20170417175846.quedtrtjmfmthv2g@art_vandelay>
Date:   Mon, 17 Apr 2017 13:58:46 -0400
From:   Sean Paul <seanpaul@...omium.org>
To:     Eric Anholt <eric@...olt.net>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/vc4: Fix refcounting of runtime PM get if it errors
 out.

On Mon, Apr 17, 2017 at 09:26:03AM -0700, Eric Anholt wrote:
> We were returning without decrementing if the error happened, meaning
> that at the next submit we wouldn't try to bring up the power domain.
> 
> Signed-off-by: Eric Anholt <eric@...olt.net>

This change looks good to me. It seems a little odd to wrap pm_runtime which
is already refcounted in another refcount, but I'm really not familiar with
the driver, and I'm sure there's a good reason for it.

Reviewed-by: Sean Paul <seanpaul@...omium.org>

> ---
> 
> I stumbled across this error when testing my CMA patch with a very low
> (64MB) CMA area -- we would oops on the submit after the one that
> failed.
> 
>  drivers/gpu/drm/vc4/vc4_gem.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
> index 777a8d9afd60..735412e3725a 100644
> --- a/drivers/gpu/drm/vc4/vc4_gem.c
> +++ b/drivers/gpu/drm/vc4/vc4_gem.c
> @@ -1016,13 +1016,16 @@ vc4_submit_cl_ioctl(struct drm_device *dev, void *data,
>  	}
>  
>  	mutex_lock(&vc4->power_lock);
> -	if (vc4->power_refcount++ == 0)
> +	if (vc4->power_refcount++ == 0) {
>  		ret = pm_runtime_get_sync(&vc4->v3d->pdev->dev);
> -	mutex_unlock(&vc4->power_lock);
> -	if (ret < 0) {
> -		kfree(exec);
> -		return ret;
> +		if (ret < 0) {
> +			mutex_unlock(&vc4->power_lock);
> +			vc4->power_refcount--;
> +			kfree(exec);
> +			return ret;
> +		}
>  	}
> +	mutex_unlock(&vc4->power_lock);
>  
>  	exec->args = args;
>  	INIT_LIST_HEAD(&exec->unref_list);
> -- 
> 2.11.0

-- 
Sean Paul, Software Engineer, Google / Chromium OS