Create 'errors' histogram for failures.

base/metrics/persistent_memory_allocator.cc

 // Copyright (c) 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 "base/metrics/persistent_memory_allocator.h"
 
 #include <assert.h>
 #include <algorithm>
 
 #if defined(OS_WIN)
@@ skipping 31 matching lines @@
 
 // TODO(bcwhite): When acceptable, consider moving flags to std::atomic<char>
 // types rather than combined bitfield.
 
 // Flags stored in the flags_ field of the SharedMetaData structure below.
 enum : int {
   kFlagCorrupt = 1 << 0,
   kFlagFull    = 1 << 1
 };
 
+// Errors that are logged in "errors" histogram.
+enum AllocatorError : int {
+  kMemoryIsCorrupt = 1,
+};
+
 bool CheckFlag(const volatile std::atomic<uint32_t>* flags, int flag) {
   uint32_t loaded_flags = flags->load(std::memory_order_relaxed);
   return (loaded_flags & flag) != 0;
 }
 
 void SetFlag(volatile std::atomic<uint32_t>* flags, int flag) {
   uint32_t loaded_flags = flags->load(std::memory_order_relaxed);
   for (;;) {
     uint32_t new_flags = (loaded_flags & ~flag) | flag;
     // In the failue case, actual "flags" value stored in loaded_flags.
@@ skipping 231 matching lines @@
                                                      uint64_t id,
                                                      base::StringPiece name,
                                                      bool readonly)
     : mem_base_(static_cast<char*>(memory.base)),
       mem_type_(memory.type),
       mem_size_(static_cast<uint32_t>(size)),
       mem_page_(static_cast<uint32_t>((page_size ? page_size : size))),
       readonly_(readonly),
       corrupt_(0),
       allocs_histogram_(nullptr),
-      used_histogram_(nullptr) {
+      used_histogram_(nullptr),
+      errors_histogram_(nullptr) {
   // These asserts ensure that the structures are 32/64-bit agnostic and meet
   // all the requirements of use within the allocator. They access private
   // definitions and so cannot be moved to the global scope.
   static_assert(sizeof(PersistentMemoryAllocator::BlockHeader) == 16,
                 "struct is not portable across different natural word widths");
   static_assert(sizeof(PersistentMemoryAllocator::SharedMetadata) == 56,
                 "struct is not portable across different natural word widths");
 
   static_assert(sizeof(BlockHeader) % kAllocAlignment == 0,
                 "BlockHeader is not a multiple of kAllocAlignment");
@@ skipping 120 matching lines @@
     return "";
   }
 
   return name_cstr;
 }
 
 void PersistentMemoryAllocator::CreateTrackingHistograms(
     base::StringPiece name) {
   if (name.empty() || readonly_)
     return;
+  std::string name_string = name.as_string();
 
-  std::string name_string = name.as_string();
+  DCHECK(!allocs_histogram_);
+  allocs_histogram_ = Histogram::FactoryGet(
+      "UMA.PersistentAllocator." + name_string + ".Allocs", 1, 10000, 50,
+      HistogramBase::kUmaTargetedHistogramFlag);
+
   DCHECK(!used_histogram_);
   used_histogram_ = LinearHistogram::FactoryGet(
       "UMA.PersistentAllocator." + name_string + ".UsedPct", 1, 101, 21,
       HistogramBase::kUmaTargetedHistogramFlag);
 
-  DCHECK(!allocs_histogram_);
-  allocs_histogram_ = Histogram::FactoryGet(
-      "UMA.PersistentAllocator." + name_string + ".Allocs", 1, 10000, 50,
+  DCHECK(!errors_histogram_);
+  errors_histogram_ = SparseHistogram::FactoryGet(
+      "UMA.PersistentAllocator." + name_string + ".Errors",
       HistogramBase::kUmaTargetedHistogramFlag);
 }
 
 size_t PersistentMemoryAllocator::used() const {
   return std::min(shared_meta()->freeptr.load(std::memory_order_relaxed),
                   mem_size_);
 }
 
 PersistentMemoryAllocator::Reference PersistentMemoryAllocator::GetAsReference(
     const void* memory,
@@ skipping 181 matching lines @@
     block->type_id.store(type_id, std::memory_order_relaxed);
     return freeptr;
   }
 }
 
 void PersistentMemoryAllocator::GetMemoryInfo(MemoryInfo* meminfo) const {
   uint32_t remaining = std::max(
       mem_size_ - shared_meta()->freeptr.load(std::memory_order_relaxed),
       (uint32_t)sizeof(BlockHeader));
   meminfo->total = mem_size_;
-  meminfo->free = IsCorrupt() ? 0 : remaining - sizeof(BlockHeader);
+  meminfo->free = remaining - sizeof(BlockHeader);
 }
 
 void PersistentMemoryAllocator::MakeIterable(Reference ref) {
   DCHECK(!readonly_);
   if (IsCorrupt())
     return;
   volatile BlockHeader* block = GetBlock(ref, 0, 0, false, false);
   if (!block)  // invalid reference
     return;
   if (block->next.load(std::memory_order_acquire) != 0)  // Already iterable.
@@ skipping 47 matching lines @@
   }
 }
 
 // The "corrupted" state is held both locally and globally (shared). The
 // shared flag can't be trusted since a malicious actor could overwrite it.
 // Because corruption can be detected during read-only operations such as
 // iteration, this method may be called by other "const" methods. In this
 // case, it's safe to discard the constness and modify the local flag and
 // maybe even the shared flag if the underlying data isn't actually read-only.
 void PersistentMemoryAllocator::SetCorrupt() const {
-  LOG(ERROR) << "Corruption detected in shared-memory segment.";
-  const_cast<std::atomic<bool>*>(&corrupt_)->store(true,
-                                                   std::memory_order_relaxed);
+  if (!corrupt_.load(std::memory_order_relaxed) &&
+      !CheckFlag(
+          const_cast<volatile std::atomic<uint32_t>*>(&shared_meta()->flags),
+          kFlagCorrupt)) {
+    LOG(ERROR) << "Corruption detected in shared-memory segment.";
+    RecordError(kMemoryIsCorrupt);
+  }
+
+  corrupt_.store(true, std::memory_order_relaxed);
   if (!readonly_) {
     SetFlag(const_cast<volatile std::atomic<uint32_t>*>(&shared_meta()->flags),
             kFlagCorrupt);
   }
 }
 
 bool PersistentMemoryAllocator::IsCorrupt() const {
   if (corrupt_.load(std::memory_order_relaxed) ||
       CheckFlag(&shared_meta()->flags, kFlagCorrupt)) {
     SetCorrupt();  // Make sure all indicators are set.
@@ skipping 41 matching lines @@
     if (type_id != 0 &&
         block->type_id.load(std::memory_order_relaxed) != type_id) {
       return nullptr;
     }
   }
 
   // Return pointer to block data.
   return reinterpret_cast<const volatile BlockHeader*>(mem_base_ + ref);
 }
 
+void PersistentMemoryAllocator::RecordError(int error) const {
+  if (errors_histogram_)
+    errors_histogram_->Add(error);
+}
+
 const volatile void* PersistentMemoryAllocator::GetBlockData(
     Reference ref,
     uint32_t type_id,
     uint32_t size) const {
   DCHECK(size > 0);
   const volatile BlockHeader* block =
       GetBlock(ref, type_id, size, false, false);
   if (!block)
     return nullptr;
   return reinterpret_cast<const volatile char*>(block) + sizeof(BlockHeader);
@@ skipping 128 matching lines @@
 
 // static
 bool FilePersistentMemoryAllocator::IsFileAcceptable(
     const MemoryMappedFile& file,
     bool read_only) {
   return IsMemoryAcceptable(file.data(), file.length(), 0, read_only);
 }
 #endif  // !defined(OS_NACL)
 
 }  // namespace base