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6722113: CMS: Incorrect overflow handling during precleaning of Reference lists

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When we encounter marking stack overflow during precleaning of Reference lists, we were using the overflow list mechanism, which can cause problems on account of mutating the mark word of the header because of conflicts with mutator accesses and updates of that field. Instead we should use the usual mechanism for overflow handling in concurrent phases, namely dirtying of the card on which the overflowed object lies. Since precleaning effectively does a form of discovered list processing, albeit with discovery enabled, we needed to adjust some code to be correct in the face of interleaved processing and discovery.

Reviewed-by: apetrusenko, jcoomes
This commit is contained in:
Y. Srinivas Ramakrishna 2008-11-20 12:27:41 -08:00
parent 28b2c4aeaf
commit db6bef2c70
5 changed files with 95 additions and 48 deletions
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46
hotspot/src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
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@ -538,6 +538,7 @@ CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
_survivor_chunk_capacity(0), // -- ditto --
_survivor_chunk_index(0), // -- ditto --
_ser_pmc_preclean_ovflw(0),
_ser_kac_preclean_ovflw(0),
_ser_pmc_remark_ovflw(0),
_par_pmc_remark_ovflw(0),
_ser_kac_ovflw(0),
@ -4388,10 +4389,10 @@ size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
CMSPrecleanRefsYieldClosure yield_cl(this);
assert(rp->span().equals(_span), "Spans should be equal");
CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
&_markStack);
&_markStack, true /* preclean */);
CMSDrainMarkingStackClosure complete_trace(this,
_span, &_markBitMap, &_markStack,
&keep_alive);
_span, &_markBitMap, &_markStack,
&keep_alive, true /* preclean */);
// We don't want this step to interfere with a young
// collection because we don't want to take CPU
@ -4852,17 +4853,19 @@ void CMSCollector::checkpointRootsFinalWork(bool asynch,
// recurrence of that condition.
assert(_markStack.isEmpty(), "No grey objects");
size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
_ser_kac_ovflw;
_ser_kac_ovflw + _ser_kac_preclean_ovflw;
if (ser_ovflw > 0) {
if (PrintCMSStatistics != 0) {
gclog_or_tty->print_cr("Marking stack overflow (benign) "
"(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
"(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
", kac_preclean="SIZE_FORMAT")",
_ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
_ser_kac_ovflw);
_ser_kac_ovflw, _ser_kac_preclean_ovflw);
}
_markStack.expand();
_ser_pmc_remark_ovflw = 0;
_ser_pmc_preclean_ovflw = 0;
_ser_kac_preclean_ovflw = 0;
_ser_kac_ovflw = 0;
}
if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
@ -5693,10 +5696,10 @@ void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
ReferenceProcessor* rp = ref_processor();
assert(rp->span().equals(_span), "Spans should be equal");
CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
&_markStack);
&_markStack, false /* !preclean */);
CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
_span, &_markBitMap, &_markStack,
&cmsKeepAliveClosure);
&cmsKeepAliveClosure, false /* !preclean */);
{
TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
if (rp->processing_is_mt()) {
@ -8302,8 +8305,29 @@ void CMSKeepAliveClosure::do_oop(oop obj) {
}
)
if (simulate_overflow || !_mark_stack->push(obj)) {
_collector->push_on_overflow_list(obj);
_collector->_ser_kac_ovflw++;
if (_concurrent_precleaning) {
// We dirty the overflown object and let the remark
// phase deal with it.
assert(_collector->overflow_list_is_empty(), "Error");
// In the case of object arrays, we need to dirty all of
// the cards that the object spans. No locking or atomics
// are needed since no one else can be mutating the mod union
// table.
if (obj->is_objArray()) {
size_t sz = obj->size();
HeapWord* end_card_addr =
(HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
MemRegion redirty_range = MemRegion(addr, end_card_addr);
assert(!redirty_range.is_empty(), "Arithmetical tautology");
_collector->_modUnionTable.mark_range(redirty_range);
} else {
_collector->_modUnionTable.mark(addr);
}
_collector->_ser_kac_preclean_ovflw++;
} else {
_collector->push_on_overflow_list(obj);
_collector->_ser_kac_ovflw++;
}
}
}
}
@ -8400,6 +8424,8 @@ const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
void CMSDrainMarkingStackClosure::do_void() {
// the max number to take from overflow list at a time
const size_t num = _mark_stack->capacity()/4;
assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
"Overflow list should be NULL during concurrent phases");
while (!_mark_stack->isEmpty() ||
// if stack is empty, check the overflow list
_collector->take_from_overflow_list(num, _mark_stack)) {