RFR(S) 8166364: fatal error: acquiring lock DirtyCardQ_CBL_mon/16 out of order with lock Module_lock/6 -- possible deadlock

[David Holmes]

Hi Harold,

Change looks good. A couple of suggestions re comments below.

On 8/10/2016 1:20 AM, harold seigel wrote:
> Hi,
>
> Please review this fix for JDK-8166364.
>
> This fix moves the setting of the module fields in the class mirrors of
> the fixup_module_list outside of the Module_lock.  The determination of
> whether a mirror should be added to the fixup_module_list is still done
> under Module_lock as is the defining of module java.base.  This prevents
> any synchronization issues with a mirror being erroneously added to the
> fixup_module_list after module java.base is defined.  The other piece is
> that the VM, in Modules::define_javabase_module(), guarantees under
> Module_lock that only one thread will ever successfully define module
> java.base.
>
> Open webrev: http://cr.openjdk.java.net/~hseigel/bug_8166364/

src/share/vm/classfile/modules.cpp

Can you add a comment here:

  246
+      // Only the thread that actually defined the base module will get 
here,
+      // so no locking is needed.
+
  247   // Patch any previously loaded class's module field with 
java.base's java.lang.reflect.Module.
  248   ModuleEntryTable::patch_javabase_entries(module_handle);

---

src/share/vm/classfile/javaClasses.cpp

This comment is no longer quite reads right now it is not the else clause:

  801     // java.base was defined at some point between calling 
create_mirror()
  802     // and obtaining the Module_lock, patch this particular class 
with java.base.

suggest:

// If java.base was already defined then patch this particular class 
with java.base.


Thanks,
David


> JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8166364
>
> The fix was tested with the JCK Lang and vm tests, and JTreg hotspot,
> java/io, java/lang, and java/util tests using both fastdebug and
> slowdebug builds.  The nsk cololocated and the non-colocated quick tests
> were also run against a slowdebug build.
>
> Thanks, Harold
>