Resolution for issue #28746: changed order in which locks/flags are grabbed in MallocHooks to preve…

runtime/vm/malloc_hooks.cc

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
 
 #if defined(DART_USE_TCMALLOC) && !defined(PRODUCT)
 
 #include "vm/malloc_hooks.h"
 
@@ skipping 155 matching lines @@
   static intptr_t original_pid_;
   static Mutex* malloc_hook_mutex_;
   static intptr_t allocation_count_;
   static intptr_t heap_allocated_memory_in_bytes_;
   static AddressMap* address_map_;
 
   static const intptr_t kInvalidPid = -1;
 };
 
 
+// MallocHookScope state.
+ThreadLocalKey MallocHookScope::in_malloc_hook_flag_ = kUnsetThreadLocalKey;
+
 // MallocHooks state / locks.
-ThreadLocalKey MallocHookScope::in_malloc_hook_flag_ = kUnsetThreadLocalKey;
 bool MallocHooksState::active_ = false;
 intptr_t MallocHooksState::original_pid_ = MallocHooksState::kInvalidPid;
 Mutex* MallocHooksState::malloc_hook_mutex_ = new Mutex();
 
 // Memory allocation state information.
 intptr_t MallocHooksState::allocation_count_ = 0;
 intptr_t MallocHooksState::heap_allocated_memory_in_bytes_ = 0;
 AddressMap* MallocHooksState::address_map_ = NULL;
 
 
@@ skipping 75 matching lines @@
   MutexLocker ml(MallocHooksState::malloc_hook_mutex());
   return MallocHooksState::heap_allocated_memory_in_bytes();
 }
 
 
 void MallocHooksState::RecordAllocHook(const void* ptr, size_t size) {
   if (MallocHookScope::IsInHook() || !MallocHooksState::IsOriginalProcess()) {
     return;
   }
 
-  // Set the malloc hook flag before grabbing the mutex to avoid calling hooks
-  // again.
-  MallocHookScope mhs;
   MutexLocker ml(MallocHooksState::malloc_hook_mutex());

[zra, 2017/02/17 18:41:02]

I think taking the log and checking Active() needs to come even before
MallocHookScope::IsInHook() etc above, otherwise we could hit the assert in
MallocHookScope::IsInHook().

[bkonyi, 2017/02/17 21:15:11]

We can't take the lock before anything else, or else we'll end up in a deadlock.
See comments in newest patch set for my proposed solution.

   if ((ptr != NULL) && MallocHooksState::Active()) {
+    // Set the malloc hook flag before to avoid calling hooks again if memory is
+    // allocated/freed below.
+    MallocHookScope mhs;
     MallocHooksState::IncrementHeapAllocatedMemoryInBytes(size);
     MallocHooksState::address_map()->Insert(ptr, size);
   }
 }
 
 
 void MallocHooksState::RecordFreeHook(const void* ptr) {
   if (MallocHookScope::IsInHook() || !MallocHooksState::IsOriginalProcess()) {
     return;
   }
 
-  // Set the malloc hook flag before grabbing the mutex to avoid calling hooks
-  // again.
-  MallocHookScope mhs;
   MutexLocker ml(MallocHooksState::malloc_hook_mutex());

[zra, 2017/02/17 18:41:02]

ditto

[bkonyi, 2017/02/17 21:15:11]

See above.

   if ((ptr != NULL) && MallocHooksState::Active()) {
+    // Set the malloc hook flag before to avoid calling hooks again if memory is
+    // allocated/freed below.
+    MallocHookScope mhs;
     intptr_t size = 0;
     if (MallocHooksState::address_map()->Lookup(ptr, &size)) {
       MallocHooksState::DecrementHeapAllocatedMemoryInBytes(size);
       MallocHooksState::address_map()->Remove(ptr);
     }
   }
 }
 
 }  // namespace dart
 
 #endif  // defined(DART_USE_TCMALLOC) && !defined(PRODUCT)