--- a/hotspot/src/share/vm/gc/g1/ptrQueue.cpp Tue Jul 18 11:09:48 2017 +0200
+++ b/hotspot/src/share/vm/gc/g1/ptrQueue.cpp Tue Jul 18 14:37:42 2017 +0200
@@ -75,16 +75,7 @@
void PtrQueue::locking_enqueue_completed_buffer(BufferNode* node) {
assert(_lock->owned_by_self(), "Required.");
-
- // We have to unlock _lock (which may be Shared_DirtyCardQ_lock) before
- // we acquire DirtyCardQ_CBL_mon inside enqueue_complete_buffer as they
- // have the same rank and we may get the "possible deadlock" message
- _lock->unlock();
-
qset()->enqueue_complete_buffer(node);
- // We must relock only because the caller will unlock, for the normal
- // case.
- _lock->lock_without_safepoint_check();
}
@@ -189,34 +180,11 @@
if (_lock) {
assert(_lock->owned_by_self(), "Required.");
- // The current PtrQ may be the shared dirty card queue and
- // may be being manipulated by more than one worker thread
- // during a pause. Since the enqueueing of the completed
- // buffer unlocks the Shared_DirtyCardQ_lock more than one
- // worker thread can 'race' on reading the shared queue attributes
- // (_buf and _index) and multiple threads can call into this
- // routine for the same buffer. This will cause the completed
- // buffer to be added to the CBL multiple times.
-
- // We "claim" the current buffer by caching value of _buf in
- // a local and clearing the field while holding _lock. When
- // _lock is released (while enqueueing the completed buffer)
- // the thread that acquires _lock will skip this code,
- // preventing the subsequent the multiple enqueue, and
- // install a newly allocated buffer below.
-
BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
_buf = NULL; // clear shared _buf field
locking_enqueue_completed_buffer(node); // enqueue completed buffer
-
- // While the current thread was enqueueing the buffer another thread
- // may have a allocated a new buffer and inserted it into this pointer
- // queue. If that happens then we just return so that the current
- // thread doesn't overwrite the buffer allocated by the other thread
- // and potentially losing some dirtied cards.
-
- if (_buf != NULL) return;
+ assert(_buf == NULL, "multiple enqueuers appear to be racing");
} else {
BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());
if (qset()->process_or_enqueue_complete_buffer(node)) {
--- a/hotspot/src/share/vm/runtime/mutex.hpp Tue Jul 18 11:09:48 2017 +0200
+++ b/hotspot/src/share/vm/runtime/mutex.hpp Tue Jul 18 14:37:42 2017 +0200
@@ -1,5 +1,5 @@
/*
- * Copyright (c) 1998, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
@@ -90,9 +90,15 @@
public:
// A special lock: Is a lock where you are guaranteed not to block while you are
- // holding it, i.e., no vm operation can happen, taking other locks, etc.
+ // holding it, i.e., no vm operation can happen, taking other (blocking) locks, etc.
+ // The rank 'access' is similar to 'special' and has the same restrictions on usage.
+ // It is reserved for locks that may be required in order to perform memory accesses
+ // that require special barriers, e.g. SATB GC barriers, that in turn uses locks.
+ // Since memory accesses should be able to be performed pretty much anywhere
+ // in the code, that requires locks required for performing accesses being
+ // inherently a bit more special than even locks of the 'special' rank.
// NOTE: It is critical that the rank 'special' be the lowest (earliest)
- // (except for "event"?) for the deadlock detection to work correctly.
+ // (except for "event" and "access") for the deadlock detection to work correctly.
// The rank native is only for use in Mutex's created by JVM_RawMonitorCreate,
// which being external to the VM are not subject to deadlock detection.
// The rank safepoint is used only for synchronization in reaching a
@@ -104,14 +110,15 @@
// at all.
enum lock_types {
event,
- special,
- suspend_resume,
- leaf = suspend_resume + 2,
- safepoint = leaf + 10,
- barrier = safepoint + 1,
- nonleaf = barrier + 1,
- max_nonleaf = nonleaf + 900,
- native = max_nonleaf + 1
+ access = event + 1,
+ special = access + 2,
+ suspend_resume = special + 1,
+ leaf = suspend_resume + 2,
+ safepoint = leaf + 10,
+ barrier = safepoint + 1,
+ nonleaf = barrier + 1,
+ max_nonleaf = nonleaf + 900,
+ native = max_nonleaf + 1
};
// The WaitSet and EntryList linked lists are composed of ParkEvents.
--- a/hotspot/src/share/vm/runtime/mutexLocker.cpp Tue Jul 18 11:09:48 2017 +0200
+++ b/hotspot/src/share/vm/runtime/mutexLocker.cpp Tue Jul 18 14:37:42 2017 +0200
@@ -181,14 +181,13 @@
def(FullGCCount_lock , PaddedMonitor, leaf, true, Monitor::_safepoint_check_never); // in support of ExplicitGCInvokesConcurrent
}
if (UseG1GC) {
+ def(SATB_Q_FL_lock , PaddedMutex , access, true, Monitor::_safepoint_check_never);
+ def(SATB_Q_CBL_mon , PaddedMonitor, access, true, Monitor::_safepoint_check_never);
+ def(Shared_SATB_Q_lock , PaddedMutex , access + 1, true, Monitor::_safepoint_check_never);
- def(SATB_Q_FL_lock , PaddedMutex , special , true, Monitor::_safepoint_check_never);
- def(SATB_Q_CBL_mon , PaddedMonitor, leaf - 1 , true, Monitor::_safepoint_check_never);
- def(Shared_SATB_Q_lock , PaddedMutex , leaf - 1 , true, Monitor::_safepoint_check_never);
-
- def(DirtyCardQ_FL_lock , PaddedMutex , special , true, Monitor::_safepoint_check_never);
- def(DirtyCardQ_CBL_mon , PaddedMonitor, leaf - 1 , true, Monitor::_safepoint_check_never);
- def(Shared_DirtyCardQ_lock , PaddedMutex , leaf - 1 , true, Monitor::_safepoint_check_never);
+ def(DirtyCardQ_FL_lock , PaddedMutex , access, true, Monitor::_safepoint_check_never);
+ def(DirtyCardQ_CBL_mon , PaddedMonitor, access, true, Monitor::_safepoint_check_never);
+ def(Shared_DirtyCardQ_lock , PaddedMutex , access + 1, true, Monitor::_safepoint_check_never);
def(FreeList_lock , PaddedMutex , leaf , true, Monitor::_safepoint_check_never);
def(SecondaryFreeList_lock , PaddedMonitor, leaf , true, Monitor::_safepoint_check_never);