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

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Message-Id: <1592051425-94019-1-git-send-email-xiyuyang19@fudan.edu.cn>
Date:   Sat, 13 Jun 2020 20:30:25 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     Christian Koenig <christian.koenig@....com>,
        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,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] drm/ttm: Fix dma_fence refcnt leak when adding move fence

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>
---
 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);

-- 
2.7.4