Request for review(M): 4930919: race condition in MDO creation at back branch locations

[Igor Veresov]

Thanks, Vladimir and Tom!

igor

On 1/10/11 6:32 PM, Tom Rodriguez wrote:
> Looks good.
>
> tom
>
> On Jan 10, 2011, at 6:23 PM, Igor Veresov wrote:
>
>> On 1/10/11 5:33 PM, Vladimir Kozlov wrote:
>>> Looks good but you don't need 'next' label.
>>>
>>
>> Right. Forgot it. Thanks!
>>
>> igor
>>
>>> Vladimir
>>>
>>> Igor Veresov wrote:
>>>> On 1/10/11 10:51 AM, Vladimir Kozlov wrote:
>>>>> Igor Veresov wrote:
>>>>>> The problem arises when a thread fails to allocate an MDO (by loosing
>>>>>> the race) and so profile_method() returns 0. And then we reload the
>>>>>> MDO pointer and see it's not null and has been just set by another
>>>>>> thread which makes us decide that the data index value the
>>>>>> profile_method() returned is valid.
>>>>>>
>>>>>> The solution is to reuse set_method_data_for_bcp() set up mdp: make
>>>>>> profile_method() just to create MDO and leave bcp->di translation for
>>>>>> set_method_data_for_bcp().
>>>>>>
>>>>>> Webrev: http://cr.openjdk.java.net/~iveresov/4930919/webrev.00/
>>>>>
>>>>> Looks good. One suggestion.
>>>>> Swapping registers in addptr() will allow you to avoid double branch:
>>>>
>>>> That's an excellent suggestion, thank you!
>>>>
>>>> igor
>>>>>
>>>>> testptr(rax, rax);
>>>>> ! jcc(Assembler::zero, set_mdp); // set mdp to zero
>>>>>
>>>>> // rbx,: method
>>>>> // rsi: bcp
>>>>> call_VM_leaf(CAST_FROM_FN_PTR(address, InterpreterRuntime::bcp_to_di),
>>>>> rbx, rsi);
>>>>> // rax,: mdi
>>>>>
>>>>> + // mdo is guaranteed to be non-zero here, we checked for it before the
>>>>> call.
>>>>> movptr(rbx, Address(rbx,
>>>>> in_bytes(methodOopDesc::method_data_offset())));
>>>>> testptr(rbx, rbx);
>>>>> jcc(Assembler::zero, zero_continue);
>>>>> addptr(rbx, in_bytes(methodDataOopDesc::data_offset()));
>>>>> - addptr(rbx, rax);
>>>>> + addptr(rax, rbx);
>>>>> + bind(set_mdp);
>>>>> - movptr(Address(rbp, frame::interpreter_frame_mdx_offset * wordSize),
>>>>> rbx);
>>>>> + movptr(Address(rbp, frame::interpreter_frame_mdx_offset * wordSize),
>>>>> rax);
>>>>>
>>>>> Vladimir
>>>>
>>
>