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8380651: [ubsan] gc/logging/TestGCId.java triggers runtime error: division by zero in shenandoahAdaptiveHeuristics

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Reviewed-by: wkemper, shade, xpeng
This commit is contained in:
Kelvin Nilsen 2026-04-17 15:30:34 +00:00
parent c3c59413be
commit 26ccc2eaa4
7 changed files with 38 additions and 25 deletions
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34
src/hotspot/share/gc/shenandoah/heuristics/shenandoahAdaptiveHeuristics.cpp
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@ -209,14 +209,14 @@ void ShenandoahAdaptiveHeuristics::choose_collection_set_from_regiondata(Shenand
}
}
void ShenandoahAdaptiveHeuristics::add_degenerated_gc_time(double timestamp, double gc_time) {
void ShenandoahAdaptiveHeuristics::add_degenerated_gc_time(double time_at_start, double gc_time) {
// Conservatively add sample into linear model If this time is above the predicted concurrent gc time
if (predict_gc_time(timestamp) < gc_time) {
add_gc_time(timestamp, gc_time);
if (predict_gc_time(time_at_start) < gc_time) {
add_gc_time(time_at_start, gc_time);
}
}
void ShenandoahAdaptiveHeuristics::add_gc_time(double timestamp, double gc_time) {
void ShenandoahAdaptiveHeuristics::add_gc_time(double time_at_start, double gc_time) {
// Update best-fit linear predictor of GC time
uint index = (_gc_time_first_sample_index + _gc_time_num_samples) % GC_TIME_SAMPLE_SIZE;
if (_gc_time_num_samples == GC_TIME_SAMPLE_SIZE) {
@ -225,10 +225,10 @@ void ShenandoahAdaptiveHeuristics::add_gc_time(double timestamp, double gc_time)
_gc_time_sum_of_xy -= _gc_time_xy[index];
_gc_time_sum_of_xx -= _gc_time_xx[index];
}
_gc_time_timestamps[index] = timestamp;
_gc_time_timestamps[index] = time_at_start;
_gc_time_samples[index] = gc_time;
_gc_time_xy[index] = timestamp * gc_time;
_gc_time_xx[index] = timestamp * timestamp;
_gc_time_xy[index] = time_at_start * gc_time;
_gc_time_xx[index] = time_at_start * time_at_start;
_gc_time_sum_of_timestamps += _gc_time_timestamps[index];
_gc_time_sum_of_samples += _gc_time_samples[index];
@ -247,18 +247,26 @@ void ShenandoahAdaptiveHeuristics::add_gc_time(double timestamp, double gc_time)
_gc_time_b = gc_time;
_gc_time_sd = 0.0;
} else if (_gc_time_num_samples == 2) {
// Two points define a line
double delta_y = gc_time - _gc_time_samples[_gc_time_first_sample_index];
double delta_x = timestamp - _gc_time_timestamps[_gc_time_first_sample_index];
_gc_time_m = delta_y / delta_x;
assert(time_at_start > _gc_time_timestamps[_gc_time_first_sample_index],
"Two GC cycles cannot finish at same time: %.6f vs %.6f, with GC times %.6f and %.6f", time_at_start,
_gc_time_timestamps[_gc_time_first_sample_index], gc_time, _gc_time_samples[_gc_time_first_sample_index]);
// Two points define a line
double delta_x = time_at_start - _gc_time_timestamps[_gc_time_first_sample_index];
double delta_y = gc_time - _gc_time_samples[_gc_time_first_sample_index];
_gc_time_m = delta_y / delta_x;
// y = mx + b
// so b = y0 - mx0
_gc_time_b = gc_time - _gc_time_m * timestamp;
_gc_time_b = gc_time - _gc_time_m * time_at_start;
_gc_time_sd = 0.0;
} else {
// Since timestamps are monotonically increasing, denominator does not equal zero.
double denominator = _gc_time_num_samples * _gc_time_sum_of_xx - _gc_time_sum_of_timestamps * _gc_time_sum_of_timestamps;
assert(denominator != 0.0, "Invariant: samples: %u, sum_of_xx: %.6f, sum_of_timestamps: %.6f",
_gc_time_num_samples, _gc_time_sum_of_xx, _gc_time_sum_of_timestamps);
_gc_time_m = ((_gc_time_num_samples * _gc_time_sum_of_xy - _gc_time_sum_of_timestamps * _gc_time_sum_of_samples) /
(_gc_time_num_samples * _gc_time_sum_of_xx - _gc_time_sum_of_timestamps * _gc_time_sum_of_timestamps));
denominator);
_gc_time_b = (_gc_time_sum_of_samples - _gc_time_m * _gc_time_sum_of_timestamps) / _gc_time_num_samples;
double sum_of_squared_deviations = 0.0;
for (size_t i = 0; i < _gc_time_num_samples; i++) {

3
src/hotspot/share/gc/shenandoah/shenandoahControlThread.cpp
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@ -346,7 +346,8 @@ void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
ShenandoahHeap* const heap = ShenandoahHeap::heap();
ShenandoahGCSession session(cause, heap->global_generation());
ShenandoahGCSession session(cause, heap->global_generation(), true,
point == ShenandoahGC::ShenandoahDegenPoint::_degenerated_outside_cycle);
heap->increment_total_collections(false);

5
src/hotspot/share/gc/shenandoah/shenandoahGenerationalControlThread.cpp
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@ -628,11 +628,10 @@ void ShenandoahGenerationalControlThread::service_stw_full_cycle(GCCause::Cause
void ShenandoahGenerationalControlThread::service_stw_degenerated_cycle(const ShenandoahGCRequest& request) {
assert(_degen_point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
request.generation->heuristics()->record_degenerated_cycle_start(ShenandoahGC::ShenandoahDegenPoint::_degenerated_outside_cycle
== _degen_point);
_heap->increment_total_collections(false);
ShenandoahGCSession session(request.cause, request.generation);
ShenandoahGCSession session(request.cause, request.generation, true,
_degen_point == ShenandoahGC::ShenandoahDegenPoint::_degenerated_outside_cycle);
ShenandoahDegenGC gc(_degen_point, request.generation);
gc.collect(request.cause);
_degen_point = ShenandoahGC::_degenerated_unset;

9
src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp
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@ -1650,7 +1650,8 @@ void ShenandoahHeap::set_active_generation(ShenandoahGeneration* generation) {
_active_generation = generation;
}
void ShenandoahHeap::on_cycle_start(GCCause::Cause cause, ShenandoahGeneration* generation) {
void ShenandoahHeap::on_cycle_start(GCCause::Cause cause, ShenandoahGeneration* generation,
bool is_degenerated, bool is_out_of_cycle) {
shenandoah_policy()->record_collection_cause(cause);
const GCCause::Cause current = gc_cause();
@ -1659,7 +1660,11 @@ void ShenandoahHeap::on_cycle_start(GCCause::Cause cause, ShenandoahGeneration*
set_gc_cause(cause);
generation->heuristics()->record_cycle_start();
if (is_degenerated) {
generation->heuristics()->record_degenerated_cycle_start(is_out_of_cycle);
} else {
generation->heuristics()->record_cycle_start();
}
}
void ShenandoahHeap::on_cycle_end(ShenandoahGeneration* generation) {

2
src/hotspot/share/gc/shenandoah/shenandoahHeap.hpp
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@ -564,7 +564,7 @@ public:
return _evac_tracker;
}
void on_cycle_start(GCCause::Cause cause, ShenandoahGeneration* generation);
void on_cycle_start(GCCause::Cause cause, ShenandoahGeneration* generation, bool is_degenerated, bool is_out_of_cycle);
void on_cycle_end(ShenandoahGeneration* generation);
ShenandoahVerifier* verifier();

7
src/hotspot/share/gc/shenandoah/shenandoahUtils.cpp
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@ -56,15 +56,14 @@ const char* ShenandoahGCSession::cycle_end_message(ShenandoahGenerationType type
}
}
ShenandoahGCSession::ShenandoahGCSession(GCCause::Cause cause, ShenandoahGeneration* generation) :
ShenandoahGCSession::ShenandoahGCSession(GCCause::Cause cause, ShenandoahGeneration* generation,
bool is_degenerated, bool is_out_of_cycle) :
_heap(ShenandoahHeap::heap()),
_generation(generation),
_timer(_heap->gc_timer()),
_tracer(_heap->tracer()) {
assert(!ShenandoahGCPhase::is_current_phase_valid(), "No current GC phase");
_heap->on_cycle_start(cause, _generation);
_heap->on_cycle_start(cause, _generation, is_degenerated, is_out_of_cycle);
_timer->register_gc_start();
_tracer->report_gc_start(cause, _timer->gc_start());
_heap->trace_heap_before_gc(_tracer);

3
src/hotspot/share/gc/shenandoah/shenandoahUtils.hpp
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@ -70,7 +70,8 @@ private:
static const char* cycle_end_message(ShenandoahGenerationType type);
public:
ShenandoahGCSession(GCCause::Cause cause, ShenandoahGeneration* generation);
ShenandoahGCSession(GCCause::Cause cause, ShenandoahGeneration* generation,
bool is_degenerated = false, bool is_out_of_cycle = false);
~ShenandoahGCSession();
};