commit 209beca0f051ff56654c2027f2e281c8a73d1686
author Mark Urbanus <urbanus@google.com> Thu Feb 23 11:16:04 2017 -0800
committer Mark Urbanus <urbanus@google.com> Thu Feb 23 11:51:16 2017 -0800
tree 09c269d1798cb1635de12f866b7ceecf501ff455
parent b0254c4293b6dce82ec6dd339f19d30cf19d3df6

Create VR HWComposer without locks held

Problem:
Surfaceflinger is occassionally deadlocking when switching to VR Mode.

Root-cause:
During the creation of the VR HWComposer through hwbinder,
hwservicemanager notifies surfaceflinger the service is available through a
binder callback. Because Surfaceflinger holds the state-lock during the
HWComposer creation, its possible all of SurfaceFlinger's binder threads are
handling other transactions waiting for the state-lock to be released.
This prevents the hwservicemanager callback ever to be handled resulting in
a deadlock.

Solution:
Don't hold the state-lock when instantiating the VR HWComposer.

Test: Validated deadlocks no longer occur when switching to VR mode.
Bug: 35680107
Change-Id: I932c81fce293a8b57983f4242432b87522ce964c

services/surfaceflinger/SurfaceFlinger.cpp

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 2781e8c..60c71b3 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -176,8 +176,10 @@
         mFrameBuckets(),
         mTotalTime(0),
         mLastSwapTime(0),
-        mNumLayers(0),
-        mEnterVrMode(false)
+        mNumLayers(0)
+#ifdef USE_HWC2
+        ,mEnterVrMode(false)
+#endif
 {
     ALOGI("SurfaceFlinger is starting");
 
@@ -1204,12 +1206,17 @@
 }
 
 void SurfaceFlinger::updateVrMode() {
+    bool enteringVrMode = mEnterVrMode;
+    if (enteringVrMode == mHwc->isUsingVrComposer()) {
+        return;
+    }
+    if (enteringVrMode && !mVrHwc) {
+        // Construct new HWComposer without holding any locks.
+        mVrHwc = new HWComposer(true);
+        ALOGV("Vr HWC created");
+    }
     {
         Mutex::Autolock _l(mStateLock);
-        bool enteringVrMode = mEnterVrMode;
-        if (enteringVrMode == mHwc->isUsingVrComposer()) {
-            return;
-        }
 
         if (enteringVrMode) {
             // Start vrflinger thread, if it hasn't been started already.
@@ -1224,11 +1231,6 @@
                 }
             }
 
-            if (!mVrHwc) {
-                mVrHwc = new HWComposer(true);
-                ALOGV("Vr HWC created");
-            }
-
             resetHwc();
 
             mHwc = mVrHwc;