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Bug ID: JDK-6948538 CMS: BOT walkers can fall into object allocation and initialization cracks
JDK-6948538 : CMS: BOT walkers can fall into object allocation and initialization cracks

Details
Type:
Bug
Submit Date:
2010-04-29
Status:
Closed
Updated Date:
2011-04-23
Project Name:
JDK
Resolved Date:
2011-04-23
Component:
hotspot
OS:
solaris,generic,solaris_10
Sub-Component:
gc
CPU:
x86,sparc,generic
Priority:
P3
Resolution:
Fixed
Affected Versions:
hs16,hs17,1.4.2,1.4.2_12,5.0u7,5.0u17,5.0u19,6u13,6u14,6u15,6u16,6u18,6u19,6u20,6u21
Fixed Versions:
hs19 (b06)

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Sub Tasks

Description
BOT walkers can sometimes observe allocated-but-not-yet-fully initialized
objects, which can cause crashes during GC (both the concurrent as well
as the stop-world phases, with the latter much more likely).

                                    

Comments
WORK AROUND

Since the bug depends on concurrent ccard-scanning with promotion into CMS,
which can only happen when using ParNew+CMS, either of the following
constitutes a workaround:-

(a) switch off CMS, OR

(b) switch off ParNew

of course, depending on platform, at potentially considerable loss in performance.
                                     
2010-04-29
EVALUATION

See 6872049 for some more background, the relevant portion of
which will be copied into this CR (by and by).
                                     
2010-04-29
SUGGESTED FIX

http://analemma.sfbay.sun.com/net/neeraja/export/ysr/cms_promo_scan/webrev

or

file:///net/neeraja.us.oracle.com/export/ysr/cms_promo_scan/webrev/index.html
                                     
2010-07-21
EVALUATION

The introduction of necessary OrderAccess::storestore for this fix revealed
a scaling issue which will be fixed in 6973570. Backports of this CR to older
releases should make sure that such backports happen together with that of
6973570 to aovid any performance regressions that would be seen if only
the fix for this CR is backported.
                                     
2010-07-30
EVALUATION

http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/be3f9c242c9d
                                     
2010-08-17



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