RFR (XS): 8062950: Bug in locking code when UseOptoBiasInlining is disabled: assert(dmw->is_neutral()) failed: invariant

[Doerr, Martin]

Hi Vladimir,

thanks for replying quickly.

Are you sure you want the swap_reg_contains_mark flag to get removed?
There's a TODO in front of the changed line:
    // TODO: optimize away redundant LDs of obj->mark and improve the markword triage
    // order to reduce the number of conditional branches in the most common cases.
    // Beware -- there's a subtle invariant that fetch of the markword
    // at [FETCH], below, will never observe a biased encoding (*101b).
    // If this invariant is not held we risk exclusion (safety) failure.

So I'm not sure if the flag may be useful again when somebody works on this TODO.

Best regards,
Martin


-----Original Message-----
From: Vladimir Kozlov [mailto:vladimir.kozlov at oracle.com] 
Sent: Donnerstag, 6. November 2014 00:31
To: Christian Thalinger; Doerr, Martin
Cc: hotspot-compiler-dev at openjdk.java.net; Hotspot dev runtime
Subject: Re: RFR (XS): 8062950: Bug in locking code when UseOptoBiasInlining is disabled: assert(dmw->is_neutral()) failed: invariant

It is our (Compiler group) code. This problem was introduced with my 
changes for RTM locking.

Martin your changes are good. But you cleanup a bit this code since we 
now never put markword to tmpReg before this call?

Thanks,
Vladimir

On 11/5/14 3:13 PM, Christian Thalinger wrote:
> I’m not exactly sure who is our biased locking expert these days but I guess it’s someone from the runtime team.  CC’ing them.
>
>> On Nov 5, 2014, at 7:38 AM, Doerr, Martin <martin.doerr at sap.com> wrote:
>>
>> Hi,
>>
>> we found a bug in MacroAssembler::fast_lock on x86 which shows up when UseOptoBiasInlining is switched off.
>> The problem is that biased_locking_enter is used with swap_reg_contains_mark==true, which is no longer correct after biased_locking_enter was put in front of check for IsInflated.
>>
>> Please review
>> http://cr.openjdk.java.net/~goetz/webrevs/8062950-lockBug/webrev.00/ <http://cr.openjdk.java.net/~goetz/webrevs/8062950-lockBug/webrev.00/>
>>
>> Best regards,
>> Martin
>