components/metrics: Add runtime memory leak detector

components/metrics/leak_detector/leak_detector.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "components/metrics/leak_detector/leak_detector.h"
+
+#include <link.h>
+#include <stdint.h>
+#include <unistd.h>
+
+#include <new>
+
+#include "base/logging.h"
+#include "components/metrics/leak_detector/leak_detector_impl.h"
+#include <gperftools/custom_allocator.h>
+#include <gperftools/malloc_extension.h>
+#include <gperftools/malloc_hook.h>
+#include <gperftools/spin_lock_wrapper.h>
+
+namespace leak_detector {
+
+namespace {
+
+// We strip out different number of stack frames in debug mode
+// because less inlining happens in that case
+#ifdef NDEBUG
+static const int kStripFrames = 2;
+#else
+static const int kStripFrames = 3;
+#endif
+
+// For storing the address range of the Chrome binary in memory.
+struct MappingInfo {
+  uintptr_t addr;
+  size_t size;
+} chrome_mapping;
+
+// TODO(sque): This is a temporary solution for leak detector params. Eventually
+// params should be passed in from elsewhere in Chromium, and this file should
+// be deleted.
+
+bool EnvToBool(const char* envname, const bool default_value) {
+  return !getenv(envname)
+      ? default_value
+      : memchr("tTyY1\0", getenv(envname)[0], 6) != NULL;
+}
+
+int EnvToInt(const char* envname, const int default_value) {
+  return !getenv(envname)
+      ? default_value
+      : strtol(getenv(envname), NULL, 10);
+}
+
+// Used for sampling allocs and frees. Randomly samples |g_sampling_factor|/256
+// of the pointers being allocated and freed.
+int g_sampling_factor = EnvToInt("LEAK_DETECTOR_SAMPLING_FACTOR", 1);
+
+// The number of call stack levels to unwind when profiling allocations by call
+// stack.
+int g_stack_depth = EnvToInt("LEAK_DETECTOR_STACK_DEPTH", 4);
+
+// Dump allocation stats and check for memory leaks after this many bytes have
+// been allocated since the last dump/check. Does not get affected by sampling.
+uint64_t g_dump_interval_bytes =
+    EnvToInt("LEAK_DETECTOR_DUMP_INTERVAL_KB", 32768) * 1024;
+
+// Enable verbose logging. Dump all leak analysis data, not just analysis
+// summaries and suspected leak reports.
+bool g_dump_leak_analysis = EnvToBool("LEAK_DETECTOR_VERBOSE", false);
+
+// The number of times an allocation size must be suspected as a leak before it
+// gets reported.
+int g_size_suspicion_threshold =
+    EnvToInt("LEAK_DETECTOR_SIZE_SUSPICION_THRESHOLD", 4);
+
+// The number of times a call stack for a particular allocation size must be
+// suspected as a leak before it gets reported.
+int g_call_stack_suspicion_threshold =
+    EnvToInt("LEAK_DETECTOR_CALL_STACK_SUSPICION_THRESHOLD", 4);
+
+// Use a simple spinlock for locking. Don't use a mutex, which can call malloc
+// and cause infinite recursion.
+SpinLockWrapper* g_heap_lock = nullptr;
+
+// Points to the active instance of the leak detector.
+// Modify this only when locked.
+LeakDetectorImpl* g_leak_detector = nullptr;
+
+// Keep track of the total number of bytes allocated.
+// Modify this only when locked.
+uint64_t g_total_alloc_size = 0;
+
+// Keep track of the total alloc size when the last dump occurred.
+// Modify this only when locked.
+uint64_t g_last_alloc_dump_size = 0;
+
+// Dump allocation stats and check for leaks after |g_dump_interval_bytes| bytes
+// have been allocated since the last time that was done. Should be called with
+// a lock since it modifies the global variable |g_last_alloc_dump_size|.
+inline void MaybeDumpStatsAndCheckForLeaks() {
+  if (g_total_alloc_size > g_last_alloc_dump_size + g_dump_interval_bytes) {
+    g_leak_detector->DumpStats();
+    g_last_alloc_dump_size = g_total_alloc_size;
+    g_leak_detector->TestForLeaks();
+  }
+}
+
+// Convert a pointer to a hash value. Returns only the upper eight bits.
+inline uint64_t PointerToHash(const void* ptr) {
+  // The input data is the pointer address, not the location in memory pointed
+  // to by the pointer.
+  const uint64_t kMultiplier = 0x9ddfea08eb382d69ULL;

[jar (doing other things), 2015/08/21 02:48:42]

Please add a comment citing the source of this hash function.  I found it on the
web in a few places... but it shouldn't be listed without an explanation or
citation.

[Simon Que, 2015/08/21 21:59:20]

Done.

+  uint64_t value = reinterpret_cast<uint64_t>(ptr) * kMultiplier;
+  return value >> 56;
+}
+
+// Uses PointerToHash() to pseudorandomly sample |ptr|.
+inline bool ShouldSample(const void* ptr) {
+  return PointerToHash(ptr) < static_cast<uint64_t>(g_sampling_factor);
+}
+
+// Allocation/deallocation hooks for MallocHook.
+void NewHook(const void* ptr, size_t size) {
+  {
+    ScopedSpinLockHolder lock(g_heap_lock);
+    g_total_alloc_size += size;
+  }
+
+  if (!ShouldSample(ptr) || !ptr || !g_leak_detector)
+    return;
+
+  // Take the stack trace outside the critical section.
+  // |g_leak_detector->ShouldGetStackTraceForSize()| is const; there is no need
+  // for a lock.
+  void* stack[g_stack_depth];
+  int depth = 0;
+  if (g_leak_detector->ShouldGetStackTraceForSize(size)) {
+    depth = MallocHook::GetCallerStackTrace(
+        stack, g_stack_depth, kStripFrames + 1);
+  }
+
+  ScopedSpinLockHolder lock(g_heap_lock);
+  g_leak_detector->RecordAlloc(ptr, size, depth, stack);
+  MaybeDumpStatsAndCheckForLeaks();
+}
+
+void DeleteHook(const void* ptr) {
+  if (!ShouldSample(ptr) || !ptr || !g_leak_detector)
+    return;
+
+  ScopedSpinLockHolder lock(g_heap_lock);
+  g_leak_detector->RecordFree(ptr);
+}
+
+// Callback for dl_iterate_phdr() to find the Chrome binary mapping.
+int IterateLoadedObjects(struct dl_phdr_info *shared_object,
+                         size_t /* size */,
+                         void *data) {
+    if (g_dump_leak_analysis) {
+      LOG(ERROR) << "name=" << shared_object->dlpi_name << ", "
+                 << "addr=" << std::hex << shared_object->dlpi_phnum;
+    }
+    for (int i = 0; i < shared_object->dlpi_phnum; i++) {
+      // Find the ELF segment header that contains the actual code of the Chrome
+      // binary.
+      const ElfW(Phdr)& segment_header = shared_object->dlpi_phdr[i];
+      if (segment_header.p_type == SHT_PROGBITS &&
+          segment_header.p_offset == 0 && data) {
+        MappingInfo* mapping = static_cast<MappingInfo*>(data);
+
+        // Make sure the fields in the ELF header and MappingInfo have the
+        // same size.
+        static_assert(sizeof(mapping->addr) == sizeof(shared_object->dlpi_addr),
+                      "Integer size mismatch between MappingInfo::addr and "
+                      "dl_phdr_info::dlpi_addr.");
+        static_assert(sizeof(mapping->size) == sizeof(segment_header.p_offset),
+                      "Integer size mismatch between MappingInfo::size and "
+                      "ElfW(Phdr)::p_memsz.");
+
+        mapping->addr = shared_object->dlpi_addr + segment_header.p_offset;
+        mapping->size = segment_header.p_memsz;
+        if (g_dump_leak_analysis) {
+          LOG(ERROR) << "Chrome mapped from " << std::hex
+                     << mapping->addr << " to "
+                     << mapping->addr + mapping->size;
+        }
+        return 1;
+      }
+    }
+    return 0;
+}
+
+}  // namespace
+
+// static
+void LeakDetector::Initialize() {
+  // If the sampling factor is too low, don't bother enabling the leak detector.
+  if (g_sampling_factor < 1) {
+    LOG(ERROR) << "Not enabling leak detector because g_sampling_factor="
+               << g_sampling_factor;
+    return;
+  }
+
+  if (IsInitialized())
+    return;
+
+  // Locate the Chrome binary mapping before doing anything else.
+  dl_iterate_phdr(IterateLoadedObjects, &chrome_mapping);
+
+  // This should be done before the hooks are set up, since it should
+  // call new, and we want that to be accounted for correctly.
+  MallocExtension::Initialize();
+
+  if (CustomAllocator::IsInitialized()) {
+    LOG(ERROR) << "Custom allocator can only be initialized once!";
+    return;
+  }
+  CustomAllocator::Initialize();
+
+  g_heap_lock = new(CustomAllocator::Allocate(sizeof(SpinLockWrapper)))
+      SpinLockWrapper;
+
+  ScopedSpinLockHolder lock(g_heap_lock);
+  if (g_leak_detector)
+    return;
+
+  LOG(ERROR) << "%d: Starting leak detector. Sampling factor: "
+             << g_sampling_factor;
+
+  g_leak_detector = new(CustomAllocator::Allocate(sizeof(LeakDetectorImpl)))
+      LeakDetectorImpl(chrome_mapping.addr,
+                       chrome_mapping.size,
+                       g_size_suspicion_threshold,
+                       g_call_stack_suspicion_threshold,
+                       g_dump_leak_analysis);
+
+  // Now set the hooks that capture new/delete and malloc/free.
+  CHECK_EQ(MallocHook::SetNewHook(&NewHook), nullptr);
+  CHECK_EQ(MallocHook::SetDeleteHook(&DeleteHook), nullptr);
+}
+
+// static
+void LeakDetector::Shutdown() {
+  {
+    ScopedSpinLockHolder lock(g_heap_lock);
+
+    if (!g_leak_detector)
+      return;
+
+    // Unset our new/delete hooks, checking they were previously set.
+    CHECK_EQ(MallocHook::SetNewHook(nullptr), &NewHook);
+    CHECK_EQ(MallocHook::SetDeleteHook(nullptr), &DeleteHook);
+
+    g_leak_detector->~LeakDetectorImpl();
+    CustomAllocator::Free(g_leak_detector, sizeof(LeakDetectorImpl));
+    g_leak_detector = nullptr;
+  }
+
+  g_heap_lock->~SpinLockWrapper();
+  CustomAllocator::Free(g_heap_lock, sizeof(*g_heap_lock));

[jar (doing other things), 2015/08/21 02:48:42]

I'm a little surprised that you can clean up this much.  This would leave this
method unsafe to call (line 245 would be dangerous), but you you have a return
on line 248 that *looks* like it is here to prevent doing a second free of the
g_leak_detector.

Can you explain the logic a bit?  I'm suspicious you should leak the lock.

[Simon Que, 2015/08/21 21:59:20]

I've fixed the logic so that it first checks for IsInitialized() and returns if
false.

Similar to the beginning of Initialize().

+
+  if (!CustomAllocator::Shutdown())
+    LOG(ERROR) <<  "Memory leak in LeakDetector, allocated objects remain.";
+
+  LOG(ERROR) << "Stopped leak detector.";
+}
+
+// static
+bool LeakDetector::IsInitialized() {
+  return g_leak_detector;
+}
+
+}  // namespace leak_detector