[PATCH 1/1] mfmediaengine: Be a bit more conservative with locks in engine Shutdown.

[Yuxuan Shui]

From: Yuxuan Shui

During engine shutdown we acquire engine lock first, then locks of its constituents (e.g. sample
grabbers); whereas normally the order is the other way around (e.g. timer callback -> acquire sample
grabber lock -> OnProcessSample callback -> engine lock). This is deadlock prone.

With this commit, engine lock is released before we shutdown the inner media session.
---
 dlls/mfmediaengine/main.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/dlls/mfmediaengine/main.c b/dlls/mfmediaengine/main.c
index 0d553a40a7e..583437ac952 100644
--- a/dlls/mfmediaengine/main.c
+++ b/dlls/mfmediaengine/main.c
@@ -2237,6 +2237,7 @@ static HRESULT WINAPI media_engine_Shutdown(IMFMediaEngineEx *iface)
 {
     struct media_engine *engine = impl_from_IMFMediaEngineEx(iface);
     HRESULT hr = S_OK;
+    IMFMediaSession *session = NULL;

TRACE("%p.\n", iface);

@@ -2247,10 +2248,16 @@ static HRESULT WINAPI media_engine_Shutdown(IMFMediaEngineEx *iface)
     {
         media_engine_set_flag(engine, FLAGS_ENGINE_SHUT_DOWN, TRUE);
         media_engine_clear_presentation(engine);
-        IMFMediaSession_Shutdown(engine->session);
+        session = engine->session;
+        IMFMediaSession_AddRef(session);
     }
     LeaveCriticalSection(&engine->cs);

+    if (session)
+    {
+        IMFMediaSession_Shutdown(session);
+        IMFMediaSession_Release(session);
+    }
     return hr;
 }