linux-kernel - Re: [PATCH] gpu: drm: remove redundant dma_fence_put() when drm_sched_job_add

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Date:   Mon, 25 Apr 2022 11:42:37 -0400
From:   Andrey Grodzovsky <andrey.grodzovsky@....com>
To:     Hangyu Hua <hbh25y@...il.com>, yuq825@...il.com, airlied@...ux.ie,
        daniel@...ll.ch
Cc:     dri-devel@...ts.freedesktop.org, lima@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] gpu: drm: remove redundant dma_fence_put() when
 drm_sched_job_add_dependency() fails

On 2022-04-25 04:36, Hangyu Hua wrote:

> When drm_sched_job_add_dependency() fails, dma_fence_put() will be called
> internally. Calling it again after drm_sched_job_add_dependency() finishes
> may result in a dangling pointer.
>
> Fix this by removing redundant dma_fence_put().
>
> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
> ---
>   drivers/gpu/drm/lima/lima_gem.c        | 1 -
>   drivers/gpu/drm/scheduler/sched_main.c | 1 -
>   2 files changed, 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/lima/lima_gem.c b/drivers/gpu/drm/lima/lima_gem.c
> index 55bb1ec3c4f7..99c8e7f6bb1c 100644
> --- a/drivers/gpu/drm/lima/lima_gem.c
> +++ b/drivers/gpu/drm/lima/lima_gem.c
> @@ -291,7 +291,6 @@ static int lima_gem_add_deps(struct drm_file *file, struct lima_submit *submit)
>   
>   		err = drm_sched_job_add_dependency(&submit->task->base, fence);
>   		if (err) {
> -			dma_fence_put(fence);
>   			return err;


Makes sense here


>   		}
>   	}
> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> index b81fceb0b8a2..ebab9eca37a8 100644
> --- a/drivers/gpu/drm/scheduler/sched_main.c
> +++ b/drivers/gpu/drm/scheduler/sched_main.c
> @@ -708,7 +708,6 @@ int drm_sched_job_add_implicit_dependencies(struct drm_sched_job *job,
>   		dma_fence_get(fence);
>   		ret = drm_sched_job_add_dependency(job, fence);
>   		if (ret) {
> -			dma_fence_put(fence);



Not sure about this one since if you look at the relevant commits -
'drm/scheduler: fix drm_sched_job_add_implicit_dependencies' and
'drm/scheduler: fix drm_sched_job_add_implicit_dependencies harder'
You will see that the dma_fence_put here balances the extra dma_fence_get
above

Andrey


>   			return ret;
>   		}
>   	}