[scudo] Only init RingBuffer when needed. (#85994)

Only attempt to initialize the ring buffer when tracking is enabled.

Updated unit tests, and added a few new unit tests to verify the
RingBuffer is not initialized by default.

Verified that the two maps associated with the RingBuffer are not
created in processes by default.

Author: cferris1000

compiler-rt/lib/scudo/standalone/combined.h

@@ -18,6 +18,7 @@
 #include "local_cache.h"
 #include "mem_map.h"
 #include "memtag.h"
+#include "mutex.h"
 #include "options.h"
 #include "quarantine.h"
 #include "report.h"
@@ -178,17 +179,17 @@ class Allocator {
     Quarantine.init(
         static_cast<uptr>(getFlags()->quarantine_size_kb << 10),
         static_cast<uptr>(getFlags()->thread_local_quarantine_size_kb << 10));
-
-    mapAndInitializeRingBuffer();
   }
 
-  void enableRingBuffer() {
+  void enableRingBuffer() NO_THREAD_SAFETY_ANALYSIS {
     AllocationRingBuffer *RB = getRingBuffer();
     if (RB)
       RB->Depot->enable();
+    RingBufferInitLock.unlock();
   }
 
-  void disableRingBuffer() {
+  void disableRingBuffer() NO_THREAD_SAFETY_ANALYSIS {
+    RingBufferInitLock.lock();
     AllocationRingBuffer *RB = getRingBuffer();
     if (RB)
       RB->Depot->disable();
@@ -915,9 +916,11 @@ class Allocator {
       DCHECK(!Primary.Options.load().get(OptionBit::TrackAllocationStacks));
       return;
     }
-    if (Track)
+
+    if (Track) {
+      initRingBufferMaybe();
       Primary.Options.set(OptionBit::TrackAllocationStacks);
-    else
+    } else
       Primary.Options.clear(OptionBit::TrackAllocationStacks);
   }
 
@@ -1092,6 +1095,9 @@ class Allocator {
                     0,
                 "invalid alignment");
 
+  // Lock to initialize the RingBuffer
+  HybridMutex RingBufferInitLock;
+
   // Pointer to memory mapped area starting with AllocationRingBuffer struct,
   // and immediately followed by Size elements of type Entry.
   atomic_uptr RingBufferAddress = {};
@@ -1546,11 +1552,16 @@ class Allocator {
         RBEntryStart)[N];
   }
 
-  void mapAndInitializeRingBuffer() {
-    if (getFlags()->allocation_ring_buffer_size <= 0)
+  void initRingBufferMaybe() {
+    ScopedLock L(RingBufferInitLock);
+    if (getRingBuffer() != nullptr)
       return;
-    u32 AllocationRingBufferSize =
-        static_cast<u32>(getFlags()->allocation_ring_buffer_size);
+
+    int ring_buffer_size = getFlags()->allocation_ring_buffer_size;
+    if (ring_buffer_size <= 0)
+      return;
+
+    u32 AllocationRingBufferSize = static_cast<u32>(ring_buffer_size);
 
     // We store alloc and free stacks for each entry.
     constexpr u32 kStacksPerRingBufferEntry = 2;

compiler-rt/lib/scudo/standalone/tests/combined_test.cpp

@@ -867,32 +867,86 @@ SCUDO_TYPED_TEST(ScudoCombinedTest, ReallocateInPlaceStress) {
   }
 }
 
+SCUDO_TYPED_TEST(ScudoCombinedTest, RingBufferDefaultDisabled) {
+  // The RingBuffer is not initialized until tracking is enabled for the
+  // first time.
+  auto *Allocator = this->Allocator.get();
+  EXPECT_EQ(0u, Allocator->getRingBufferSize());
+  EXPECT_EQ(nullptr, Allocator->getRingBufferAddress());
+}
+
+SCUDO_TYPED_TEST(ScudoCombinedTest, RingBufferInitOnce) {
+  auto *Allocator = this->Allocator.get();
+  Allocator->setTrackAllocationStacks(true);
+
+  auto RingBufferSize = Allocator->getRingBufferSize();
+  ASSERT_GT(RingBufferSize, 0u);
+  auto *RingBufferAddress = Allocator->getRingBufferAddress();
+  EXPECT_NE(nullptr, RingBufferAddress);
+
+  // Enable tracking again to verify that the initialization only happens once.
+  Allocator->setTrackAllocationStacks(true);
+  ASSERT_EQ(RingBufferSize, Allocator->getRingBufferSize());
+  EXPECT_EQ(RingBufferAddress, Allocator->getRingBufferAddress());
+}
+
 SCUDO_TYPED_TEST(ScudoCombinedTest, RingBufferSize) {
   auto *Allocator = this->Allocator.get();
-  auto Size = Allocator->getRingBufferSize();
-  ASSERT_GT(Size, 0u);
-  EXPECT_EQ(Allocator->getRingBufferAddress()[Size - 1], '\0');
+  Allocator->setTrackAllocationStacks(true);
+
+  auto RingBufferSize = Allocator->getRingBufferSize();
+  ASSERT_GT(RingBufferSize, 0u);
+  EXPECT_EQ(Allocator->getRingBufferAddress()[RingBufferSize - 1], '\0');
 }
 
 SCUDO_TYPED_TEST(ScudoCombinedTest, RingBufferAddress) {
   auto *Allocator = this->Allocator.get();
-  auto *Addr = Allocator->getRingBufferAddress();
-  EXPECT_NE(Addr, nullptr);
-  EXPECT_EQ(Addr, Allocator->getRingBufferAddress());
+  Allocator->setTrackAllocationStacks(true);
+
+  auto *RingBufferAddress = Allocator->getRingBufferAddress();
+  EXPECT_NE(RingBufferAddress, nullptr);
+  EXPECT_EQ(RingBufferAddress, Allocator->getRingBufferAddress());
+}
+
+SCUDO_TYPED_TEST(ScudoCombinedTest, StackDepotDefaultDisabled) {
+  // The StackDepot is not initialized until tracking is enabled for the
+  // first time.
+  auto *Allocator = this->Allocator.get();
+  EXPECT_EQ(0u, Allocator->getStackDepotSize());
+  EXPECT_EQ(nullptr, Allocator->getStackDepotAddress());
+}
+
+SCUDO_TYPED_TEST(ScudoCombinedTest, StackDepotInitOnce) {
+  auto *Allocator = this->Allocator.get();
+  Allocator->setTrackAllocationStacks(true);
+
+  auto StackDepotSize = Allocator->getStackDepotSize();
+  EXPECT_GT(StackDepotSize, 0u);
+  auto *StackDepotAddress = Allocator->getStackDepotAddress();
+  EXPECT_NE(nullptr, StackDepotAddress);
+
+  // Enable tracking again to verify that the initialization only happens once.
+  Allocator->setTrackAllocationStacks(true);
+  EXPECT_EQ(StackDepotSize, Allocator->getStackDepotSize());
+  EXPECT_EQ(StackDepotAddress, Allocator->getStackDepotAddress());
 }
 
 SCUDO_TYPED_TEST(ScudoCombinedTest, StackDepotSize) {
   auto *Allocator = this->Allocator.get();
-  auto Size = Allocator->getStackDepotSize();
-  ASSERT_GT(Size, 0u);
-  EXPECT_EQ(Allocator->getStackDepotAddress()[Size - 1], '\0');
+  Allocator->setTrackAllocationStacks(true);
+
+  auto StackDepotSize = Allocator->getStackDepotSize();
+  EXPECT_GT(StackDepotSize, 0u);
+  EXPECT_EQ(Allocator->getStackDepotAddress()[StackDepotSize - 1], '\0');
 }
 
 SCUDO_TYPED_TEST(ScudoCombinedTest, StackDepotAddress) {
   auto *Allocator = this->Allocator.get();
-  auto *Addr = Allocator->getStackDepotAddress();
-  EXPECT_NE(Addr, nullptr);
-  EXPECT_EQ(Addr, Allocator->getStackDepotAddress());
+  Allocator->setTrackAllocationStacks(true);
+
+  auto *StackDepotAddress = Allocator->getStackDepotAddress();
+  EXPECT_NE(StackDepotAddress, nullptr);
+  EXPECT_EQ(StackDepotAddress, Allocator->getStackDepotAddress());
 }
 
 SCUDO_TYPED_TEST(ScudoCombinedTest, StackDepot) {