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

[Vladimir Kozlov]

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 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.

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