RFR: 8213486: SIGSEGV in CompiledMethod::cleanup_inline_caches_impl with AOT

dean.long at oracle.com dean.long at oracle.com
Tue Nov 20 18:21:33 UTC 2018

OK.  I agree it makes sense to move the unloading from CompiledMethod to 
nmethod.  I was just curious what problem you were running into with AOT,
because the iterators look OK to me.  You probably ran into trouble here:

// Clean inline caches pointing to both zombie and not_entrant methods 
*if* (clean_all 
<https://java.se.oracle.com/source/s?defs=clean_all&project=jdk-jdk> || 
|| nm 
|| (nm 
<https://java.se.oracle.com/source/s?defs=code&project=jdk-jdk>() != nm 
<https://java.se.oracle.com/source/s?defs=nm&project=jdk-jdk>)) {

because !is_in_use() would be false for the not_used state.


On 11/20/18 3:12 AM, Erik Österlund wrote:
> Hi Dean,
> Yeah I think I misunderstood what I observed. So what I know is that 
> in the code cache unloading, I'm not getting all is_alive() AOT 
> methods into my iterator, which messes up the assumptions made by the 
> epoch based scheme for AOT methods.
> I noticed that in AOTCodeHeap::sweep_dependent_methods(int* indexes, 
> int methods_cnt) we make AOTCompiledMethods "invalid" in the AOT heap, 
> making it no longer observable from the iterators. Then it calls the 
> VM_Deoptimize vm operation after. Throughout all this, the 
> AOTCompiledMethod is alive(), yet when the iterators ask for all 
> is_alive() AOTCompiledMethods, it won't be visible. But I suppose IC 
> caches may still reference these methods and check if it is_unloading, 
> and then we blow up. There may possibly be multiple ways for 
> is_alive() AOTCompiledMethods to not be visible from iterators yet be 
> visible through IC caches using the "invalid" state in the .
> Anyway, the fix is the same: stop doing the epoch state thingey for 
> is_unloading() on AOTCompiledMethod where it isn't needed, and doesn't 
> seem to play well with the rather different life cycle it has, and 
> just return false instead.
> Thanks,
> /Erik
> On 2018-11-20 00:00, dean.long at oracle.com wrote:
>> Hi Erik,
>> On 11/19/18 12:42 PM, Erik Österlund wrote:
>>> ...except it looks like for AOTCompiledMethods when running with 
>>> tiered compilation, may first be is_alive(), then become !is_alive() 
>>> for a while, and then get resurrected to is_alive() using 
>>> make_entrant().
>> this doesn't sounds quite right.  AOTCompiledMethods aren't allowed 
>> to transition to zombie (!alive), only not_used or not_entrant, which 
>> should still have is_alive() returning true. Maybe some code is using 
>> is_not_entrant() instead of !is_alive()?
>> dl

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