Re: RFR (XXXS): 8221584: SIGSEGV in os::PlatformEvent::unpark() in JvmtiRawMonitor::raw_exit while posting method exit event

[David Holmes]

Thanks Robbin. I guess between the three of us we have this covered one 
way or another. :)

David
On 8/04/2019 5:13 pm, Robbin Ehn wrote:
On 4/8/19 7:27 AM, David Holmes wrote:
On 8/04/2019 3:07 pm, Stefan Karlsson wrote:
Looks good!

+1

Thanks, Robbin (I can be reviewer)


Thanks - do you want to be co-contributor or a reviewer?  :)

David

StefanK

On 2019-04-08 03:49, David Holmes wrote:
Bug: https://bugs.openjdk.java.net/browse/JDK-8221584
webrev: http://cr.openjdk.java.net/~dholmes/8221584/webrev/

I'm really just sponsoring this fix as the problem was diagnozed by 
Robbin Ehn and Stefan Karlsson - thanks guys! :) So they are the 
contributors and I'm already one Reviewer.

There's a missing loadstore barrier between extracting the ParkEvent 
from an ObjectWaiter node, and setting the node's TState to allow 
the the entering thread to proceed. It seems our recent update to 
gcc 8.2 resulted in the compiler reordering those two actions, 
meaning that the Objectwaiter pointer could now be pointing into a 
stack location with random contents. That might manifest as a SEGV 
or we may treat random memory as a pthread_mutex_t and get an EINVAL 
(or potentially other errors) on pthread_mutex_lock.

Testing: mach5 tiers 1-3 (sanity - the added barrier can't break 
anything)

Thanks,
David