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From:   Sasha Levin <sashal@kernel.org>
To:     linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc:     Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Xin Tan <tanxin.ctf@gmail.com>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
        Sasha Levin <sashal@kernel.org>,
        dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org,
        linaro-mm-sig@lists.linaro.org
Subject: [PATCH AUTOSEL 5.7 06/53] drm/ttm: Fix dma_fence refcnt leak in ttm_bo_vm_fault_reserved
Date:   Wed,  1 Jul 2020 21:21:15 -0400
Message-Id: <20200702012202.2700645-6-sashal@kernel.org>
In-Reply-To: <20200702012202.2700645-1-sashal@kernel.org>
References: <20200702012202.2700645-1-sashal@kernel.org>
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From: Xiyu Yang <xiyuyang19@fudan.edu.cn>

[ Upstream commit 37cc4b95d13f311c04aa8e9daacca3905ad45ca7 ]

ttm_bo_vm_fault_reserved() invokes dma_fence_get(), which returns a
reference of the specified dma_fence object to "moving" with increased
refcnt.

When ttm_bo_vm_fault_reserved() returns, local variable "moving" becomes
invalid, so the refcount should be decreased to keep refcount balanced.

The reference counting issue happens in several exception handling paths
of ttm_bo_vm_fault_reserved(). When those error scenarios occur such as
"err" equals to -EBUSY, 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@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/370219/
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index 0ad30b1129821..72100b84c7a90 100644
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -300,8 +300,10 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
 			break;
 		case -EBUSY:
 		case -ERESTARTSYS:
+			dma_fence_put(moving);
 			return VM_FAULT_NOPAGE;
 		default:
+			dma_fence_put(moving);
 			return VM_FAULT_SIGBUS;
 		}
 
-- 
2.25.1