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

[Christian Hagedorn]

Thank you Vladimir for your review!

Best regards,
Christian

On 15.07.20 19:37, Vladimir Kozlov wrote:
> Looks good.
> 
> Thanks,
> Vladimir K
> 
> On 7/15/20 12:58 AM, Christian Hagedorn wrote:
>> Hi Vladimir
>>
>> On 14.07.20 20:46, Vladimir Kozlov wrote:
>>> 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, I added these changes in a new webrev:
>> http://cr.openjdk.java.net/~chagedorn/8247743/webrev.02/
>>
>> Best regards,
>> Christian
>>
>>
>>> 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 
>>>>>>>