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From:   Xiyu Yang <xiyuyang19@fudan.edu.cn>
To:     Harry Wentland <harry.wentland@amd.com>,
        Leo Li <sunpeng.li@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>,
        "David (ChunMing) Zhou" <David1.Zhou@amd.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>,
        Jun Lei <Jun.Lei@amd.com>, Anthony Koo <Anthony.Koo@amd.com>,
        Zhan Liu <Zhan.Liu@amd.com>, Eric Yang <Eric.Yang2@amd.com>,
        Wenjing Liu <Wenjing.Liu@amd.com>,
        Chris Park <Chris.Park@amd.com>, Roman Li <Roman.Li@amd.com>,
        David Galiffi <David.Galiffi@amd.com>,
        Lucy Li <lucy.li@amd.com>, Paul Hsieh <paul.hsieh@amd.com>,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Cc:     yuanxzhang@fudan.edu.cn, kjlu@umn.edu,
        Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Xin Tan <tanxin.ctf@gmail.com>
Subject: [PATCH] drm/amdgpu/display: Fix dc_sink refcnt leak in dc_link_detect_helper
Date:   Thu, 23 Apr 2020 13:03:11 +0800
Message-Id: <1587618202-13283-1-git-send-email-xiyuyang19@fudan.edu.cn>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

dc_link_detect_helper() invokes dc_sink_retain(), which increases the
refcount of the "prev_sink".

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

The reference counting issue happens in one exception handling path of
dc_link_detect_helper(). When alt mode times out, the function forgets
to decrease the refcnt increased by dc_sink_retain(), causing a refcnt
leak.

Fix this issue by calling dc_sink_release() when alt mode times out.

Signed-off-by: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@gmail.com>
---
 drivers/gpu/drm/amd/display/dc/core/dc_link.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/gpu/drm/amd/display/dc/core/dc_link.c b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
index a09119c10d7c..91550d9a1abb 100644
--- a/drivers/gpu/drm/amd/display/dc/core/dc_link.c
+++ b/drivers/gpu/drm/amd/display/dc/core/dc_link.c
@@ -832,6 +832,8 @@ static bool dc_link_detect_helper(struct dc_link *link,
 
 				/* if alt mode times out, return false */
 				if (wait_for_alt_mode(link) == false) {
+					if (prev_sink != NULL)
+						dc_sink_release(prev_sink);
 					return false;
 				}
 			}
-- 
2.7.4