review (S) for 6965671: fatal error: acquiring lock JNIGlobalHandle_lock/16 out of order with lock CodeCache_lock/1

[Tom Rodriguez]

On Jul 1, 2010, at 2:36 PM, Vladimir Kozlov wrote:

> You did not explain your changes for cb->name().

That was just a clean up I've been wanting to do.  There was a time then only some of the CodeBlob subclasses had name() methods but now it's part of CodeBlob so that logic is unnecessary.

> Why we don't lock nmethod in sweeper during CodeCache walk but lock here?

nmethodLocker protects you from the sweeper so the sweeper doesn't need protection.

tom

> 
> Thanks,
> Vladimir
> 
> On 7/1/10 1:58 PM, Tom Rodriguez wrote:
>> http://cr.openjdk.java.net/~never/6965671/
>> 
>> 6965671: fatal error: acquiring lock JNIGlobalHandle_lock/16 out of order with lock CodeCache_lock/1
>> Reviewed-by:
>> 
>> The jmethodID fix created a deadlock because of lock ordering when
>> walking the CodeCache to generate CompiledMethodLoad events.  The walk
>> is performed with the CodeCache_lock held but we need to acquire the
>> JNIGlobalHandle_lock to make a jmethodID.  I considered switching back
>> to collecting the methodOop instead of the jmethodID under the lock
>> but inspection of the code made it clear that there's a preexisting
>> problem with GC of the methodOops stored into the nmethodDesc.
>> Instead I switched to a simpler implementation that holds the
>> CodeCache_lock while walking the CodeCache but releases the lock to
>> actually perform the notify.  This simplifies the code greatly as well
>> as fixing the bug.
>> 
>> Tested with NSK jvmti,jdi,jdb,hprof,jit,regression and JDI_REGRESSION
>> tests.