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Commit 209beca0 authored by Mark Urbanus's avatar Mark Urbanus
Browse files

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
parent b0254c42

services/surfaceflinger/SurfaceFlinger.cpp

+13 −11
Original line number Diff line number Diff line
@@ -176,8 +176,10 @@ SurfaceFlinger::SurfaceFlinger() 
        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::resetHwc() { 
}



void SurfaceFlinger::updateVrMode() {

    {

        Mutex::Autolock _l(mStateLock);

    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);



        if (enteringVrMode) {

            // Start vrflinger thread, if it hasn't been started already.
@@ -1224,11 +1231,6 @@ void SurfaceFlinger::updateVrMode() { 
                }

            }



            if (!mVrHwc) {

                mVrHwc = new HWComposer(true);

                ALOGV("Vr HWC created");

            }



            resetHwc();



            mHwc = mVrHwc;