Defensive code for alloc/dealloc during TLS teardown (#161)

* Defensive code for alloc/dealloc during TLS teardown

If an allocation or deallocation occurs during TLS teardown, then it is
possible for a new allocator to be created and then this is leaked. On
the mimalloc-bench mstressN benchmark this was observed leading to a
large memory leak.

This fix, detects if we are in the TLS teardown phase, and if so,
the calls to alloc or dealloc must return the allocator once they have
perform the specific operation.

Uses a separate variable to represent if a thread_local's destructor has
run already.  This is used to detect thread teardown to put the
allocator into a special slow path to avoid leaks.

* Added some printing first operation to track progress

* Improve error messages on posix

Flush errors, print assert details, and present stack traces.

* Detect incorrect use of pool.

* Clang format.

* Replace broken LL/SC implementation

LL/SC implementation was broken, this replaces it with
a locking implementation. Changes the API to support LL/SC
for future implementation on ARM.

* Improve TLS teardown.

* Make std::function fully inlined.

* Factor out PALLinux stack trace.

* Add checks for leaking allocators.

* Add release build of Windows Clang

CMakeLists.txt

@@ -147,6 +147,10 @@ if(NOT DEFINED SNMALLOC_ONLY_HEADER_LIBRARY)
     set(CMAKE_EXE_LINKER_FLAGS_RELEASE "${CMAKE_EXE_LINKER_FLAGS_RELEASE} /DEBUG")
   else()
     add_compile_options(-fno-exceptions -fno-rtti -g -ftls-model=initial-exec -fomit-frame-pointer)
+    if(SNMALLOC_CI_BUILD OR (${CMAKE_BUILD_TYPE} MATCHES "Debug"))
+      # Get better stack traces in CI and Debug.
+      target_link_libraries(snmalloc_lib INTERFACE "-rdynamic")
+    endif()
 
     if((${CMAKE_SYSTEM_PROCESSOR} STREQUAL "x86_64") OR
        (${CMAKE_SYSTEM_PROCESSOR} STREQUAL "x86") OR

azure-pipelines.yml

@@ -224,7 +224,11 @@ jobs:
     matrix:
       64-bit Debug Clang:
         BuildType: Debug
-        CMakeArgs: '-GNinja -DCMAKE_C_COMPILER="C:/Program Files/LLVM/bin/clang.exe" -DCMAKE_CXX_COMPILER="C:/Program Files/LLVM/bin/clang++.exe"'
+        CMakeArgs: '-GNinja -DCMAKE_C_COMPILER="C:/Program Files/LLVM/bin/clang-cl.exe" -DCMAKE_CXX_COMPILER="C:/Program Files/LLVM/bin/clang-cl.exe" -DCMAKE_RC_COMPILER="C:/Program Files/LLVM/bin/llvm-rc"'
+        JFlag: -j 4
+      64-bit Release Clang:
+        BuildType: Release
+        CMakeArgs: '-GNinja -DCMAKE_C_COMPILER="C:/Program Files/LLVM/bin/clang-cl.exe" -DCMAKE_CXX_COMPILER="C:/Program Files/LLVM/bin/clang-cl.exe" -DCMAKE_RC_COMPILER="C:/Program Files/LLVM/bin/llvm-rc"'
         JFlag: -j 4
 
   steps:
@@ -237,15 +241,13 @@ jobs:
       choco install --accept-license -y Ninja llvm
     displayName: 'Dependencies'
 
-  - task: CMake@1
-    displayName: 'CMake .. $(CMakeArgs) -DCMAKE_BUILD_TYPE=$(BuildType) -DSNMALLOC_CI_BUILD=On -DSNMALLOC_RUST_SUPPORT=On'
-    inputs:
-      cmakeArgs: '.. $(CMakeArgs) -DCMAKE_BUILD_TYPE=$(BuildType) -DSNMALLOC_CI_BUILD=On -DSNMALLOC_RUST_SUPPORT=On'
-
-  - task: CMake@1
-    displayName: 'CMake --build . --config ${BuildType}'
-    inputs:
-      cmakeArgs: '--build . --config ${BuildType}'
+  - script: |
+      call "C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Auxiliary\Build\vcvars64.bat"
+      mkdir build
+      cd build
+      cmake .. $(CMakeArgs) -DCMAKE_BUILD_TYPE=$(BuildType) -DSNMALLOC_CI_BUILD=On -DSNMALLOC_RUST_SUPPORT=On
+      cmake --build . --config ${BuildType}
+    displayName: 'build'
 
   - script: |
       set PATH=%PATH%;"C:\Program Files\LLVM\bin\"

src/ds/aba.h

@@ -2,13 +2,25 @@
 
 #include "bits.h"
 
+/**
+ * This file contains an abstraction of ABA protection. This API should be
+ * implementable with double-word compare and exchange or with load-link
+ * store conditional.
+ *
+ * We provide a lock based implementation.
+ */
 namespace snmalloc
 {
+#ifndef NDEBUG
+  // LL/SC typically can only perform one operation at a time
+  // check this on other platforms using a thread_local.
+  inline thread_local bool operation_in_flight = false;
+#endif
+#ifdef PLATFORM_IS_X86
   template<typename T, Construction c = RequiresInit>
   class ABA
   {
   public:
-#ifdef PLATFORM_IS_X86
     struct alignas(2 * sizeof(std::size_t)) Linked
     {
       T* ptr;
@@ -28,21 +40,12 @@ namespace snmalloc
       sizeof(Linked) == (2 * sizeof(std::size_t)),
       "Expecting ABA to be the size of two pointers");
 
-    using Cmp = Linked;
-#else
-    using Cmp = T*;
-#endif
-
   private:
-#ifdef PLATFORM_IS_X86
     union
     {
       alignas(2 * sizeof(std::size_t)) std::atomic<Linked> linked;
       Independent independent;
     };
-#else
-    std::atomic<T*> raw;
-#endif
 
   public:
     ABA()
@@ -53,66 +56,116 @@ namespace snmalloc
 
     void init(T* x)
     {
-#ifdef PLATFORM_IS_X86
       independent.ptr.store(x, std::memory_order_relaxed);
       independent.aba.store(0, std::memory_order_relaxed);
-#else
-      raw.store(x, std::memory_order_relaxed);
-#endif
     }
 
-    T* peek()
-    {
-      return
-#ifdef PLATFORM_IS_X86
-        independent.ptr.load(std::memory_order_relaxed);
-#else
-        raw.load(std::memory_order_relaxed);
-#endif
-    }
+    struct Cmp;
 
     Cmp read()
     {
-      return
-#ifdef PLATFORM_IS_X86
-        Cmp{independent.ptr.load(std::memory_order_relaxed),
-            independent.aba.load(std::memory_order_relaxed)};
-#else
-        raw.load(std::memory_order_relaxed);
-#endif
+#  ifndef NDEBUG
+      if (operation_in_flight)
+        error("Only one inflight ABA operation at a time is allowed.");
+      operation_in_flight = true;
+#  endif
+      return Cmp{{independent.ptr.load(std::memory_order_relaxed),
+                  independent.aba.load(std::memory_order_relaxed)},
+                 this};
     }
 
-    static T* ptr(Cmp& from)
+    struct Cmp
     {
-#ifdef PLATFORM_IS_X86
-      return from.ptr;
-#else
-      return from;
-#endif
-    }
+      Linked old;
+      ABA* parent;
 
-    bool compare_exchange(Cmp& expect, T* value)
-    {
-#ifdef PLATFORM_IS_X86
+      T* ptr()
+      {
+        return old.ptr;
+      }
+
+      bool store_conditional(T* value)
+      {
 #  if defined(_MSC_VER) && defined(SNMALLOC_VA_BITS_64)
-      return _InterlockedCompareExchange128(
-        (volatile __int64*)&linked,
-        (__int64)(expect.aba + (uintptr_t)1),
-        (__int64)value,
-        (__int64*)&expect);
+        auto result = _InterlockedCompareExchange128(
+          (volatile __int64*)parent,
+          (__int64)(old.aba + (uintptr_t)1),
+          (__int64)value,
+          (__int64*)&old);
 #  else
 #    if defined(__GNUC__) && !defined(__GCC_HAVE_SYNC_COMPARE_AND_SWAP_16)
 #error You must compile with -mcx16 to enable 16-byte atomic compare and swap.
 #    endif
-      Cmp xchg{value, expect.aba + 1};
+        Linked xchg{value, old.aba + 1};
+        std::atomic<Linked>& addr = parent->linked;
+
+        auto result = addr.compare_exchange_weak(
+          old, xchg, std::memory_order_relaxed, std::memory_order_relaxed);
+#  endif
+        return result;
+      }
 
-      return linked.compare_exchange_weak(
-        expect, xchg, std::memory_order_relaxed, std::memory_order_relaxed);
+      ~Cmp()
+      {
+#  ifndef NDEBUG
+        operation_in_flight = false;
 #  endif
+      }
+
+      Cmp(const Cmp&) = delete;
+    };
+  };
 #else
-      return raw.compare_exchange_weak(
-        expect, value, std::memory_order_relaxed, std::memory_order_relaxed);
-#endif
+  /**
+   * Naive implementation of ABA protection using a spin lock.
+   */
+  template<typename T, Construction c = RequiresInit>
+  class ABA
+  {
+    std::atomic<T*> ptr = nullptr;
+    std::atomic_flag lock = ATOMIC_FLAG_INIT;
+
+  public:
+    struct Cmp;
+
+    Cmp read()
+    {
+      while (lock.test_and_set(std::memory_order_acquire))
+        Aal::pause();
+
+#  ifndef NDEBUG
+      if (operation_in_flight)
+        error("Only one inflight ABA operation at a time is allowed.");
+      operation_in_flight = true;
+#  endif
+
+      return Cmp{this};
     }
+
+    struct Cmp
+    {
+      ABA* parent;
+
+    public:
+      T* ptr()
+      {
+        return parent->ptr;
+      }
+
+      bool store_conditional(T* t)
+      {
+        parent->ptr = t;
+        return true;
+      }
+
+      ~Cmp()
+      {
+        parent->lock.clear(std::memory_order_release);
+#  ifndef NDEBUG
+        operation_in_flight = false;
+#  endif
+      }
+    };
   };
+#endif
 } // namespace snmalloc

src/ds/defines.h

@@ -36,6 +36,9 @@ namespace snmalloc
   void error(const char* const str);
 } // namespace snmalloc
 
+#define TOSTRING(expr) TOSTRING2(expr)
+#define TOSTRING2(expr) #expr
+
 #ifdef NDEBUG
 #  define SNMALLOC_ASSERT(expr) \
     {}
@@ -44,7 +47,8 @@ namespace snmalloc
     { \
       if (!(expr)) \
       { \
-        snmalloc::error("assert fail"); \
+        snmalloc::error("assert fail: " #expr " in " __FILE__ \
+                        " on " TOSTRING(__LINE__)); \
       } \
     }
 #endif

src/ds/mpmcstack.h

@@ -29,9 +29,9 @@ namespace snmalloc
 
       do
       {
-        T* top = ABAT::ptr(cmp);
+        T* top = cmp.ptr();
         last->next.store(top, std::memory_order_release);
-      } while (!stack.compare_exchange(cmp, first));
+      } while (!cmp.store_conditional(first));
     }
 
     T* pop()
@@ -44,13 +44,13 @@ namespace snmalloc
 
       do
       {
-        top = ABAT::ptr(cmp);
+        top = cmp.ptr();
 
         if (top == nullptr)
           break;
 
         next = top->next.load(std::memory_order_acquire);
-      } while (!stack.compare_exchange(cmp, next));
+      } while (!cmp.store_conditional(next));
 
       return top;
     }
@@ -63,11 +63,11 @@ namespace snmalloc
 
       do
       {
-        top = ABAT::ptr(cmp);
+        top = cmp.ptr();
 
         if (top == nullptr)
           break;
-      } while (!stack.compare_exchange(cmp, nullptr));
+      } while (!cmp.store_conditional(nullptr));
 
       return top;
     }