RFR(M): 8210754: print_location is not reliable enough (printing register info)

Doerr, Martin martin.doerr at sap.com
Mon Sep 17 05:41:25 UTC 2018

Hi David,

thanks for looking at my proposal.

I'm aware of that the new code accesses memory which may be mutated concurrently.
But I'm convinced that this is far better than what we currently have. Analyzing the state of a crashed VM can never be 100% safe.

I could use try_lock to improve this situation. When I get the lock, fine.
But what should we do when the lock is held by the code which has crashed?
I think we shouldn't wait for any lock. It's better to risk errors due to concurrent mutation which seems to be not so likely.

Best regards,

-----Original Message-----
From: David Holmes <david.holmes at oracle.com> 
Sent: Montag, 17. September 2018 07:07
To: Doerr, Martin <martin.doerr at sap.com>; hotspot-runtime-dev at openjdk.java.net
Subject: Re: RFR(M): 8210754: print_location is not reliable enough (printing register info)

Hi Martin,

On 15/09/2018 12:03 AM, Doerr, Martin wrote:
> Hi,
> I'd like to make os::print_location more reliable which is used in error reporting step "printing register info". Oops and Klasses should get inspected more carefully.

But some of what you are doing is accessing shared state that could be 
mutated concurrently with the error reporting thread that is trying to 
read it e.g. walking the ClassLoaderDataGraph!


> I have seen errors like "[error occurred during error reporting (printing register info), id 0xe0000000, Internal Error (/usr/work/d056149/openjdk/jdk/src/hotspot/share/oops/klass.inline.hpp:63)]" in many hs_err files.
> Bug:
> https://bugs.openjdk.java.net/browse/JDK-8210754
> Webrev:
> http://cr.openjdk.java.net/~mdoerr/8210754_print_location/webrev.00/
> Sometimes, I get such errors when using -XX:+CrashGCForDumpingJavaThread, sometimes when injecting crashing code into compiled methods which I did by the following code:
> http://cr.openjdk.java.net/~mdoerr/crash_C2_method/webrev.00/
> I can also contribute this if it's desired. Automatic tests would certainly be nice to have. Maybe I can find some time for that.
> Please review.
> Best regards,
> Martin

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