[scudo] Deallocate the AllocatorRingBuffer too in unmapTestOnly

The AllocatorRingBuffer is allocated dynamically when Allocator is
initialized. This patch adds a corresponding deinitialization call in
unmapTestOnly, to avoid running out of virtual memory if the tests are run
a large number of times on memory-constrained platforms.

Reviewed By: Chia-hungDuan

Differential Revision: https://reviews.llvm.org/D149266

Author: fabio-d

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

@@ -178,7 +178,7 @@ class Allocator {
         static_cast<uptr>(getFlags()->quarantine_size_kb << 10),
         static_cast<uptr>(getFlags()->thread_local_quarantine_size_kb << 10));
 
-    initRingBuffer();
+    mapAndInitializeRingBuffer();
   }
 
   // Initialize the embedded GWP-ASan instance. Requires the main allocator to
@@ -228,6 +228,7 @@ class Allocator {
   }
 
   void unmapTestOnly() {
+    unmapRingBuffer();
     TSDRegistry.unmapTestOnly(this);
     Primary.unmapTestOnly();
     Secondary.unmapTestOnly();
@@ -1508,17 +1509,16 @@ class Allocator {
         &RawRingBuffer[sizeof(AllocationRingBuffer)])[N];
   }
 
-  void initRingBuffer() {
+  void mapAndInitializeRingBuffer() {
     u32 AllocationRingBufferSize =
         static_cast<u32>(getFlags()->allocation_ring_buffer_size);
     if (AllocationRingBufferSize < 1)
       return;
-    MapPlatformData Data = {};
     RawRingBuffer = static_cast<char *>(
         map(/*Addr=*/nullptr,
             roundUp(ringBufferSizeInBytes(AllocationRingBufferSize),
                     getPageSizeCached()),
-            "AllocatorRingBuffer", /*Flags=*/0, &Data));
+            "AllocatorRingBuffer"));
     auto *RingBuffer = reinterpret_cast<AllocationRingBuffer *>(RawRingBuffer);
     RingBuffer->Size = AllocationRingBufferSize;
     static_assert(sizeof(AllocationRingBuffer) %
@@ -1527,6 +1527,11 @@ class Allocator {
                   "invalid alignment");
   }
 
+  void unmapRingBuffer() {
+    unmap(RawRingBuffer, roundUp(getRingBufferSize(), getPageSizeCached()));
+    RawRingBuffer = nullptr;
+  }
+
   static constexpr size_t ringBufferSizeInBytes(u32 AllocationRingBufferSize) {
     return sizeof(AllocationRingBuffer) +
            AllocationRingBufferSize *