linux-kernel - [PATCH AUTOSEL 5.4 05/40] drm/ttm: Fix dma_fence refcnt leak when adding move fence

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Date:   Wed,  1 Jul 2020 21:23:26 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>,
        Christian König <christian.koenig@....com>,
        Sasha Levin <sashal@...nel.org>,
        dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org
Subject: [PATCH AUTOSEL 5.4 05/40] drm/ttm: Fix dma_fence refcnt leak when adding move fence

From: Xiyu Yang <xiyuyang19@...an.edu.cn>

[ Upstream commit 11425c4519e2c974a100fc984867046d905b9380 ]

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-by: Christian König <christian.koenig@....com>
Link: https://patchwork.freedesktop.org/patch/370221/
Signed-off-by: Christian König <christian.koenig@....com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 abf165b2f64fc..3ce8ad7603c7f 100644
--- a/drivers/gpu/drm/ttm/ttm_bo.c
+++ b/drivers/gpu/drm/ttm/ttm_bo.c
@@ -941,8 +941,10 @@ 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);
 
-- 
2.25.1