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noah_r
Journeyman III

cl_command_queue reference count does not track cl_event instances and leads to segmentation fault

I have discovered what I consider to be a bug in the reference tracking for cl_command_queue instances that leads to a segmentation fault under a reasonable usage scenario.

The cl_command_queue reference count is not incremented when a cl_event instance is created.  It should be.

clReleaseCommandQueue can be called while there are still cl_event instances that have not been released.  Now, in this case, it is still possible to get a reference to the command queue associated with cl_event by calling clGetEventInfo ( cl_event event, CL_EVENT_COMMAND_QUEUE, , &queue ... ).

I experience a segmentation fault if I use that queue reference to get information about the command queue,  for example:  clGetCommandQueueInfo( command_queue, CL_QUEUE_DEVICE, ...)

I've attached a bug demo program to demonstrate the error.

My output shows the queue reference count is unaffected by the event lifecycle:

$ g++ -o bugDemo command_queue_ref_cnt_demo.cpp bugDemoSupport.cpp -I /opt/AMDAPP/include -lOpenCL

$ ./bugDemo

Selected CL_PLATFORM_NAME: AMD Accelerated Parallel Processing

CL_DEVICE_NAME: AMD Opteron(TM) Processor 6274

CL_DRIVER_VERSION: 1214.3 (sse2,avx,fma4)

reference count after instantiation:       context 2, queue 1

reference count after creating an event:   context 4, queue 1

reference count after releasing the event: context 3, queue 1

The Apple implementation does not suffer this problem.  The queue reference count tracks the number of event instances associated with that queue:

$ ./bugDemo

Selected CL_PLATFORM_NAME: Apple

CL_DEVICE_NAME: Intel(R) Core(TM) i7-3615QM CPU @ 2.30GHz

CL_DRIVER_VERSION: 1.1

reference count after instantiation:       context 2, queue 1

reference count after creating an event:   context 4, queue 2

reference count after releasing the event: context 3, queue 1

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3 Replies
sudarshan
Staff
Staff

Re: cl_command_queue reference count does not track cl_event instances and leads to segmentation fault

Hi Noah,

Thanks for the code. We will try to reproduce it and get back.

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dipak
Staff
Staff

Re: cl_command_queue reference count does not track cl_event instances and leads to segmentation fault

Hi,

Sorry for this late reply.

I ran your code but haven't found any segmentation fault. Please find my observations given below:

-----------------------------------------------------------------------------------------------------------------

Selected CL_PLATFORM_NAME: AMD Accelerated Parallel Processing

CL_DEVICE_NAME: Turks

CL_DRIVER_VERSION: 1214.3

reference count after instantiation:       context 2, queue 1

reference count after creating an event:   context 4, queue 1

reference count after releasing the event: context 3, queue 1

The End

--------------------------------------------------------------------------------------------------------------

/////////////////////////////////////////////////////////////////

After changing the " selected_OpenCL_device_index = 1; " in file bugDemoSupport.cpp.

---------------------------------------------------------------------------------------------------------------

Selected CL_PLATFORM_NAME: AMD Accelerated Parallel Processing

CL_DEVICE_NAME: Intel(R) Core(TM) i5-3230M CPU @ 2.60GHz

CL_DRIVER_VERSION: 1214.3 (sse2,avx)

reference count after instantiation:       context 2, queue 1

reference count after creating an event:   context 4, queue 1

reference count after releasing the event: context 3, queue 1

The End

------------------------------------------------------------------------------------------------------------

As per you, "The cl_command_queue reference count is not incremented when a cl_event instance is created.  It should be."

Please can you elaborate your point or refer any document/link that suggests this point.

Regards,

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pinform
Staff
Staff

Re: cl_command_queue reference count does not track cl_event instances and leads to segmentation fault

Hi Noak,

Is your problem resolved?  Can you post an update?

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