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Avoid unconditional spinlock bounce in AllocationSampleList::ReportMalloc. #1328

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Merged
copybara-service merged 1 commit into from
Oct 13, 2026
Merged

Avoid unconditional spinlock bounce in AllocationSampleList::ReportMalloc. #1328

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27 changes: 17 additions & 10 deletions tcmalloc/allocation_sample.h
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Original file line number Diff line number Diff line change
Expand Up @@ -15,10 +15,12 @@
#ifndef TCMALLOC_ALLOCATION_SAMPLE_H_
#define TCMALLOC_ALLOCATION_SAMPLE_H_

#include <atomic>
#include <memory>

#include "absl/base/const_init.h"
#include "absl/base/internal/spinlock.h"
#include "absl/base/optimization.h"
#include "absl/base/thread_annotations.h"
#include "absl/time/time.h"
#include "tcmalloc/internal/config.h"
Expand Down Expand Up @@ -54,30 +56,35 @@ class AllocationSampleList {

void Add(AllocationSample* absl_nonnull as TCMALLOC_CAPTURED_BY_THIS) {
AllocationGuardSpinLockHolder h(lock_);
as->next_ = first_;
first_ = as;
as->next_ = first_.load(std::memory_order_relaxed);
first_.store(as, std::memory_order_release);
}

// This list is very short and we're nowhere near a hot path, just walk
void Remove(AllocationSample* absl_nonnull as) {
AllocationGuardSpinLockHolder h(lock_);
AllocationSample** link = &first_;
AllocationSample* cur = first_;
while (cur != as) {
TC_CHECK_NE(cur, nullptr);
link = &cur->next_;
AllocationSample* cur = first_.load(std::memory_order_relaxed);
if (cur == as) {
first_.store(as->next_, std::memory_order_release);
return;
}
while (cur != nullptr && cur->next_ != as) {
cur = cur->next_;
}
*link = as->next_;
TC_CHECK_NE(cur, nullptr);
cur->next_ = as->next_;
}

void ReportMalloc(const struct StackTrace& sample) {
// Check that StackTrace was zero-initialized so we don't leak uninitialized
// memory (potentially holding cryptographic material) into core dumps.
TC_CHECK(sample.depth == kMaxStackDepth ||
sample.stack[sample.depth] == nullptr);
if (ABSL_PREDICT_TRUE(first_.load(std::memory_order_acquire) == nullptr)) {
return;
}
AllocationGuardSpinLockHolder h(lock_);
AllocationSample* cur = first_;
AllocationSample* cur = first_.load(std::memory_order_relaxed);
while (cur != nullptr) {
cur->mallocs_->AddTrace(1.0, sample);
cur = cur->next_;
Expand All @@ -89,7 +96,7 @@ class AllocationSampleList {
// samples. Invoking `new` while holding this lock can lead to deadlock.
absl::base_internal::SpinLock lock_{
absl::base_internal::SCHEDULE_KERNEL_ONLY};
AllocationSample* absl_nullable first_ ABSL_GUARDED_BY(lock_) = nullptr;
std::atomic<AllocationSample* absl_nullable> first_{nullptr};
};

} // namespace tcmalloc::tcmalloc_internal
Expand Down
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