[FELIX-6252] Deadlock in SCR ComponentRegistry updateChangeCount

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: scr-2.1.16
• Fix Version/s: scr-2.1.18
• Component/s: Declarative Services (SCR)
• Assignee: Carsten Ziegeler
• Reporter: Karl Pauls
• Created: 07/Apr/20 10:02
• Updated: 16/Apr/20 14:33
• Resolved: 07/Apr/20 10:51

Description

There is a possible deadlock in the ComponentRegistry and it goes like this:

The update of the change count is setting up a timer to execute a task while it is holding a lock. The task in turn, is grabbing that lock when activated and calls into the service registry while holding the lock. 

Now, when a service gets unregistered that is coming from a factory - the service registry will do an upcall that triggers scr to update the change count and hence, trying to grab the lock mentioned above.

That can cause a case where the task has the lock and is waiting in the service registry which is waiting on scr, which is waiting for the lock.

E.g.:

For the tasks:

  java.lang.Thread.State: WAITING (parking)
	at sun.misc.Unsafe.park(Native Method)
	- parking to wait for <0x00000007bc02ea40> (a java.util.concurrent.CountDownLatch$Sync)
	at java.util.concurrent.locks.LockSupport.park(LockSupport.java:175)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.parkAndCheckInterrupt(AbstractQueuedSynchronizer.java:836)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.doAcquireSharedInterruptibly(AbstractQueuedSynchronizer.java:997)
	at java.util.concurrent.locks.AbstractQueuedSynchronizer.acquireSharedInterruptibly(AbstractQueuedSynchronizer.java:1304)
	at java.util.concurrent.CountDownLatch.await(CountDownLatch.java:231)
	at org.apache.felix.framework.ServiceRegistry.getService(ServiceRegistry.java:368)
	at org.apache.felix.framework.EventDispatcher.filterListenersUsingHooks(EventDispatcher.java:618)
	at org.apache.felix.framework.EventDispatcher.fireServiceEvent(EventDispatcher.java:542)
	at org.apache.felix.framework.Felix.fireServiceEvent(Felix.java:4833)
	at org.apache.felix.framework.Felix.access$000(Felix.java:112)
	at org.apache.felix.framework.Felix$1.serviceChanged(Felix.java:434)
	at org.apache.felix.framework.ServiceRegistry.servicePropertiesModified(ServiceRegistry.java:612)
	at org.apache.felix.framework.ServiceRegistrationImpl.setProperties(ServiceRegistrationImpl.java:132)
	at org.apache.felix.scr.impl.ComponentRegistry$4.run(ComponentRegistry.java:743)
	- locked <0x000000074376fb00> (a java.lang.Object)
	at java.util.TimerThread.mainLoop(Timer.java:555)
	at java.util.TimerThread.run(Timer.java:505)

and for the update:

  java.lang.Thread.State: BLOCKED (on object monitor)    at org.apache.felix.scr.impl.ComponentRegistry.updateChangeCount(ComponentRegistry.java:722)    - waiting to lock <0x000000074376fb00> (a java.lang.Object)    at org.apache.felix.scr.impl.BundleComponentActivator.updateChangeCount(BundleComponentActivator.java:778)    at org.apache.felix.scr.impl.manager.AbstractComponentManager.setState(AbstractComponentManager.java:1420)    at org.apache.felix.scr.impl.manager.SingleComponentManager.getServiceInternal(SingleComponentManager.java:962)    at org.apache.felix.scr.impl.manager.SingleComponentManager.getService(SingleComponentManager.java:900)    at org.apache.felix.framework.ServiceRegistrationImpl.getFactoryUnchecked(ServiceRegistrationImpl.java:348)    at org.apache.felix.framework.ServiceRegistrationImpl.getService(ServiceRegistrationImpl.java:248)    at org.apache.felix.framework.ServiceRegistry.getService(ServiceRegistry.java:350)    at org.apache.felix.framework.EventDispatcher.filterListenersUsingHooks(EventDispatcher.java:618)    at org.apache.felix.framework.EventDispatcher.fireServiceEvent(EventDispatcher.java:542)    at org.apache.felix.framework.Felix.fireServiceEvent(Felix.java:4833)    at org.apache.felix.framework.Felix.access$000(Felix.java:112)    at org.apache.felix.framework.Felix$1.serviceChanged(Felix.java:434)    at org.apache.felix.framework.ServiceRegistry.unregisterService(ServiceRegistry.java:170)

Carsten Ziegeler, could you have a look and see if that is fixable by not holding the lock while calling into the serviceregistry?