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

[Igor Veresov]

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