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Commit ff0f38e6 authored by Dave Sparks's avatar Dave Sparks
Browse files

Fix potential deadlock in stopPreview/stopRecord. 

Some camera HALs spin up a preview thread and need to wait for
the thread to exit. This can create a potential deadlock. In
stopPreview, we take the main lock. If a preview callback occurs
while the lock is held, the preview thread will block. If the
camera HAL is waiting for the preview thread to exit, this will
cause a deadlock.

This patch breaks out the preview buffer heap into a separate
mutex. This mutex is never held when the main lock is held, thus
preventing the deadlock from occuring.
parent 3bde289d

camera/libcameraservice/CameraService.cpp

+43 −28
Original line number Diff line number Diff line
@@ -683,6 +683,8 @@ void CameraService::Client::stopPreview() 
{

    LOGD("stopPreview (pid %d)", getCallingPid());



    // hold main lock during state transition

    {

        Mutex::Autolock lock(mLock);

        if (checkPid() != NO_ERROR) return;
@@ -698,14 +700,22 @@ void CameraService::Client::stopPreview() 
        if (mSurface != 0 && !mUseOverlay) {

            mSurface->unregisterBuffers();

        }

    }



    // hold preview buffer lock

    {

        Mutex::Autolock lock(mPreviewLock);

        mPreviewBuffer.clear();

    }

}



// stop recording mode

void CameraService::Client::stopRecording()

{

    LOGD("stopRecording (pid %d)", getCallingPid());



    // hold main lock during state transition

    {

        Mutex::Autolock lock(mLock);

        if (checkPid() != NO_ERROR) return;
@@ -722,9 +732,14 @@ void CameraService::Client::stopRecording() 
        mHardware->stopRecording();

        mHardware->disableMsgType(CAMERA_MSG_VIDEO_FRAME);

        LOGD("stopRecording(), hardware stopped OK");

    }



    // hold preview buffer lock

    {

        Mutex::Autolock lock(mPreviewLock);

        mPreviewBuffer.clear();

    }

}



// release a recording frame

void CameraService::Client::releaseRecordingFrame(const sp<IMemory>& mem)
@@ -1216,10 +1231,10 @@ void CameraService::Client::copyFrameAndPostCopiedFrame(const sp<ICameraClient>& 
    // provided it's big enough. Don't allocate the memory or

    // perform the copy if there's no callback.



    // hold the lock while we grab a reference to the preview buffer

    // hold the preview lock while we grab a reference to the preview buffer

    sp<MemoryHeapBase> previewBuffer;

    {

        Mutex::Autolock lock(mLock);

        Mutex::Autolock lock(mPreviewLock);

        if (mPreviewBuffer == 0) {

            mPreviewBuffer = new MemoryHeapBase(size, 0, NULL);

        } else if (size > mPreviewBuffer->virtualSize()) {

camera/libcameraservice/CameraService.h

+3 −1
Original line number Diff line number Diff line
@@ -181,7 +181,6 @@ private: 
        mutable     Condition                   mReady;

                    sp<CameraService>           mCameraService;

                    sp<ISurface>                mSurface;

                    sp<MemoryHeapBase>          mPreviewBuffer;

                    int                         mPreviewCallbackFlag;



                    sp<MediaPlayer>             mMediaPlayerClick;
@@ -197,6 +196,9 @@ private: 
                    sp<OverlayRef>              mOverlayRef;

                    int                         mOverlayW;

                    int                         mOverlayH;



        mutable     Mutex                       mPreviewLock;

                    sp<MemoryHeapBase>          mPreviewBuffer;

    };



// ----------------------------------------------------------------------------