RFR(xs): 8014022: G1: Non Java threads should lock the shared SATB queue lock without safepoint checks.

[Jon Masamitsu]

Per,

In a product build what was the symptom of this bug that
you observed?

Jon

On 6/27/13 6:00 AM, Per Liden wrote:
> Hi,
>
> Could I please have a couple of reviews on this small fix.
>
> Summary: If a non-Java thread writes to an object field the G1 
> pre-barrier can potentially safepoint when acquiring the shared 
> pointer queue lock (Shared_SATB_Q_lock). This is problematic if e.g. 
> the non-Java thread has joined the STS. The solution is to grab the 
> lock without a safepoint check.
>
> Testing: I ran into this bug while doing some (unrelated) experiments 
> with G1, where I had a non-JavaThread do calls to 
> oop->obj_field_put(). Hotspot doesn't currently have any 
> non-JavaThread which does this, so it can't currently be provoked by a 
> test. However, after fixing this in my experimental repo I stopped 
> running into this issue.
>
> Webrev: http://cr.openjdk.java.net/~pliden/8014022/webrev.00/
>
> Bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8014022
>
> /Per
>
> (btw, Bengt volunteered to sponsor the change)