linux-kernel - Re: [PATCH] drm/ttm: Fix dma_fence refcnt leak when adding move fence

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Date:   Mon, 15 Jun 2020 10:55:25 +0200
From:   Christian König <christian.koenig@....com>
To:     Xiyu Yang <xiyuyang19@...an.edu.cn>, Huang Rui <ray.huang@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linaro-mm-sig@...ts.linaro.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu,
        Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH] drm/ttm: Fix dma_fence refcnt leak when adding move fence

Am 13.06.20 um 14:30 schrieb Xiyu Yang:
> ttm_bo_add_move_fence() invokes dma_fence_get(), which returns a
> reference of the specified dma_fence object to "fence" with increased
> refcnt.
>
> When ttm_bo_add_move_fence() returns, local variable "fence" becomes
> invalid, so the refcount should be decreased to keep refcount balanced.
>
> The reference counting issue happens in one exception handling path of
> ttm_bo_add_move_fence(). When no_wait_gpu flag is equals to true, the
> function forgets to decrease the refcnt increased by dma_fence_get(),
> causing a refcnt leak.
>
> Fix this issue by calling dma_fence_put() when no_wait_gpu flag is
> equals to true.
>
> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>

Reviewed and pushed this one as well as the other ttm fix to drm-misc-fixes.

That should show up in Linus tree rather soon.

Thanks for the help,
Christian.

PS: Are you working on some new automated scripts to catch that stuff or 
how did you stumbled over it?

> ---
>   drivers/gpu/drm/ttm/ttm_bo.c | 4 +++-
>   1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/ttm/ttm_bo.c b/drivers/gpu/drm/ttm/ttm_bo.c
> index f73b81c2576e..0f20e14a4cfd 100644
> --- a/drivers/gpu/drm/ttm/ttm_bo.c
> +++ b/drivers/gpu/drm/ttm/ttm_bo.c
> @@ -883,8 +883,10 @@ static int ttm_bo_add_move_fence(struct ttm_buffer_object *bo,
>   	if (!fence)
>   		return 0;
>   
> -	if (no_wait_gpu)
> +	if (no_wait_gpu) {
> +		dma_fence_put(fence);
>   		return -EBUSY;
> +	}
>   
>   	dma_resv_add_shared_fence(bo->base.resv, fence);
>