[16] RFR(S): 8247743: Segmentation fault in debug builds due to stack overflow in find_recur with deep graphs

[Vladimir Kozlov]

Can you move next up to where other small find*() methods are defined?:

+Node* Node::find_ctrl(int idx) {
+  return find(idx, true);
  }

Also add '// not PRODUCT' comment to #endif for #ifndef PRODUCT. It is hard to find where this not product code ends.

Looks good otherwise.

Thanks,
Vladimir

On 7/14/20 2:54 AM, Christian Hagedorn wrote:
> Hi Vladimir
> 
> On 13.07.20 19:43, Vladimir Kozlov wrote:
>> Node::find_ctrl() is used during debugging when you want to print and look on only control nodes.
>> We have several such methods which are only used in debugger.
> 
> I see, I restored this method and changed Node::find() accordingly. I additionally added two find_ctrl() methods to make 
> it easier to call it from a debugger (as already present for find_node()).
> 
>> I suggest to store old_arena() in local var and pass into add_to_worklist().
>>
>> You can make add_to_worklist() static since you pass node as argument.
> 
> Okay. I updated this and the change above in a new webrev:
> http://cr.openjdk.java.net/~chagedorn/8247743/webrev.01/
> 
> Best regards,
> Christian
> 
>> Thanks,
>> Vladimir
>>
>> On 7/13/20 3:09 AM, Christian Hagedorn wrote:
>>> Ping - could anyone review it, please? Thanks!
>>>
>>> Best regards,
>>> Christian
>>>
>>> On 02.07.20 09:33, Christian Hagedorn wrote:
>>>> Hi
>>>>
>>>> Please review the following patch:
>>>> https://bugs.openjdk.java.net/browse/JDK-8247743
>>>> http://cr.openjdk.java.net/~chagedorn/8247743/webrev.00/
>>>>
>>>> The testcase creates a deep graph with a lot of nodes on a chain. When running with the specified test flags, it 
>>>> recursively calls Node::find_recur() for each node discovered which eventually results in a segmentation fault due 
>>>> to a stack overflow (around 10000 calls due to such a long chain of nodes). The fix just converts the recursive 
>>>> algorithm into an iterative one to avoid a segmentation fault. This is similar to JDK-8246203 [1].
>>>>
>>>> I additionally removed Node::find_ctrl() and its special handling in the algorithm since it is not used.
>>>>
>>>> There is actually another problem with the recursive version. When running the testcase without 
>>>> -XX:CompileOnly=compiler/c2/TestFindNode, it will spin forever inside [2] because there is a debug_orig node cycle 
>>>> and the loop does not break based on the debug_orig nodes being visited. This is also fixed in the patch.
>>>>
>>>> Thank you!
>>>>
>>>> Best regards,
>>>> Christian
>>>>
>>>>
>>>> [1] https://bugs.openjdk.java.net/browse/JDK-8246203
>>>> [2] http://hg.openjdk.java.net/jdk/jdk/file/e2622818f0bd/src/hotspot/share/opto/node.cpp#l1589