RFR(s): 8218147: make_walkable asserts on multiple calls

[Robbin Ehn]

Hi, please review.

After reexamine this issue:
Threads in native must always have their stack walkable.
JFR sampler should never need to make a stack walkable (for native sample).

I manage to locally reproduce reliable with changes to JFR sampler and having
hundreds of threads running similar code as the in the bug.
(Looping creating an array with negative size.)

I found a place where we don't proper look at the suspend flags.
The java thread can thus escape native and make it's stack unwalkable and later
it tries to make it walkable at the same time as the JFR sampler.

By removing some kind of fast check and instead always call the 
check_safepoint_and_suspend_for_native_trans I can no longer reproduce.
(which have the JFR native trans suspend check)
And it passes t1-5.

Code:
http://cr.openjdk.java.net/~rehn/8218147/v3/webrev/
Issue:
https://bugs.openjdk.java.net/browse/JDK-8218147

Thanks, Robbin

On 4/5/19 5:43 PM, Robbin Ehn wrote:
> Hi Dean,
> 
> Sorry, I missed this mail.
> Yes we can do that.
> Ignore my other mail, I'll update.
> 
> Thanks, Robbin
> 
> 
> dean.long at oracle.com skrev: (5 april 2019 09:22:24 CEST)
>> On 4/4/19 5:16 PM, dean.long at oracle.com wrote:
>>>
>>>>>
>>>>> If it's already set, should we check that _last_Java_pc matches the
>>
>>>>> new value?
>>>>
>>>> We manually set the pc in several places, so if it's set, it's not
>>>> certain that
>>>> it should be the same as in last sp.
>>>> I can't distinguish between the cases.
>>>>
>>>
>>> If we get pc from sp[-1] then it should match, but you're right, we
>>> sometimes get pc from somewhere else.
>>
>> How about if we combine the !walkable check and the
>> capture_last_Java_pc() logic into a single method?
>> Then we can do something like:
>>
>>      if (!walkable()) {
>>          address pc = (address)_last_Java_sp[-1];
>>          address a = Atomic::cmpxchg(pc, &_last_Java_pc, NULL);
>>          assert(a == NULL || a == pc, "unexpected PC %p", a);
>>      }
>>
>> dl