linux-kernel - Re: [PATCH v2] drm/v3d: fix missing unlock

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Date:   Fri, 28 Jan 2022 11:55:10 -0100
From:   Melissa Wen <mwen@...lia.com>
To:     Yongzhi Liu <lyz_cs@....edu.cn>
Cc:     emma@...olt.net, airlied@...ux.ie, daniel@...ll.ch,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2] drm/v3d: fix missing unlock

On 01/27, Yongzhi Liu wrote:
> [why]
> Unlock is needed on the error handling path to prevent dead lock.
> v3d_submit_cl_ioctl and v3d_submit_csd_ioctl is missing unlock.
> 
> [how]
> Fix this by change goto target on the error handling path.
s/change/changing/g

I would just say: `Changing the goto to target an error handling path
that includes drm_gem_unlock reservations.`

and drop the explanation below

> As unlock is handle in fail_unreserve, i keep the failures
> handling around there. So the goto targets a place between
> `fail_unreserve:` and `fail:`.
> 
> Signed-off-by: Yongzhi Liu <lyz_cs@....edu.cn>
> ---
>  drivers/gpu/drm/v3d/v3d_gem.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
> index c7ed2e1..d9c7b39 100644
> --- a/drivers/gpu/drm/v3d/v3d_gem.c
> +++ b/drivers/gpu/drm/v3d/v3d_gem.c
> @@ -798,7 +798,7 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
>  
>  		if (!render->base.perfmon) {
>  			ret = -ENOENT;
> -			goto fail;
> +			goto v3d_unlock;
We usually use a `fail` prefix when handling failures.
A suggestion: `fail_perfmon` ?
>  		}
>  	}
>  
> @@ -847,6 +847,7 @@ v3d_submit_cl_ioctl(struct drm_device *dev, void *data,
>  
>  fail_unreserve:
>  	mutex_unlock(&v3d->sched_lock);
> +v3d_unlock:
>  	drm_gem_unlock_reservations(last_job->bo,
>  				    last_job->bo_count, &acquire_ctx);
>  fail:
> @@ -1027,7 +1028,7 @@ v3d_submit_csd_ioctl(struct drm_device *dev, void *data,
>  						     args->perfmon_id);
>  		if (!job->base.perfmon) {
>  			ret = -ENOENT;
> -			goto fail;
> +			goto v3d_unlock;
>  		}
>  	}
>  
> @@ -1056,6 +1057,7 @@ v3d_submit_csd_ioctl(struct drm_device *dev, void *data,
>  
>  fail_unreserve:
>  	mutex_unlock(&v3d->sched_lock);
> +v3d_unlock:
>  	drm_gem_unlock_reservations(clean_job->bo, clean_job->bo_count,
>  				    &acquire_ctx);
>  fail:

With these changes, you can include in the next version my r-b:
Reviewed-by: Melissa Wen <mwen@...lia.com>

> -- 
> 2.7.4
> 

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