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Fix a GCC race condition leading to crashes on shutdown #358

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Fix a GCC race condition leading to crashes on shutdown #358

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6 changes: 3 additions & 3 deletions tcmalloc/static_vars.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -106,9 +106,9 @@ ABSL_CONST_INIT NumaTopology<kNumaPartitions, kNumBaseClasses>
Static::numa_topology_;
ABSL_CONST_INIT GwpAsanState Static::gwp_asan_state_;
ABSL_CONST_INIT Static::PerSizeClassCounts Static::per_size_class_counts_;
TCMALLOC_ATTRIBUTE_NO_DESTROY ABSL_CONST_INIT SystemAllocator<
NumaTopology<kNumaPartitions, kNumBaseClasses>, kNormalPartitions>
Static::system_allocator_{numa_topology_, kMinMmapAlloc};
TCMALLOC_ATTRIBUTE_NO_DESTROY ABSL_CONST_INIT
Static::SystemAllocatorStorage Static::system_allocator_{numa_topology_,
kMinMmapAlloc};
// Force kInvalidSpan to be read-protected. Span contains a std::atomic, and
// libc++'s std::atomic implementation contains a mutable field in one of its
// implementation details. This prevents Span from being placed in a read-only
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23 changes: 20 additions & 3 deletions tcmalloc/static_vars.h
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Expand Up @@ -115,7 +115,7 @@ class Static final {
static SystemAllocator<NumaTopology<kNumaPartitions, kNumBaseClasses>,
kNormalPartitions>&
system_allocator() {
return system_allocator_;
return system_allocator_.allocator;
}

static Arena& arena() { return arena_; }
Expand Down Expand Up @@ -252,8 +252,25 @@ class Static final {
static PageAllocatorStorage page_allocator_;
static PageMap pagemap_;

ABSL_CONST_INIT static SystemAllocator<
NumaTopology<kNumaPartitions, kNumBaseClasses>, kNormalPartitions>
// Avoid destruction of SystemAllocator in a way that works with constinit and
// C++17. Once C++17 support is dropped this can be replaced with
// absl::NoDestructor. absl::NoDestructor uses a placement new, which doesn't
// work with constinit in C++17. Destruction is especially dangerous here
// because it can lead to race conditions and crashes on shutdown.
union SystemAllocatorStorage {
constexpr SystemAllocatorStorage(
const NumaTopology<kNumaPartitions, kNumBaseClasses>& topology,
size_t min_mmap_size)
: allocator(topology, min_mmap_size) {}

~SystemAllocatorStorage() {}

SystemAllocator<NumaTopology<kNumaPartitions, kNumBaseClasses>,
kNormalPartitions>
allocator;
};

TCMALLOC_ATTRIBUTE_NO_DESTROY ABSL_CONST_INIT static SystemAllocatorStorage
system_allocator_;

static ABSL_ATTRIBUTE_SECTION_VARIABLE(.data.rel.ro) const Span kInvalidSpan;
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