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

[Stefan Karlsson]

Looks good!

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