Fix race condition when dump providers invoked within destroyed state

base/trace_event/memory_dump_manager.cc

Index: base/trace_event/memory_dump_manager.cc
diff --git a/base/trace_event/memory_dump_manager.cc b/base/trace_event/memory_dump_manager.cc
index 35b27d9a03a0a0212b0f807e83068881f3d4395b..286a824a4b0207bca63ed70a4d1ee51dfa7efd53 100644
--- a/base/trace_event/memory_dump_manager.cc
+++ b/base/trace_event/memory_dump_manager.cc
@@ -407,8 +407,14 @@ void MemoryDumpManager::SetupNextMemoryDump(
   // (for discounting trace memory overhead) while holding the |lock_|.
   TraceLog::GetInstance()->InitializeThreadLocalEventBufferIfSupported();
 
-  // If this was the last hop, create a trace event, add it to the trace and
-  // finalize process dump (invoke callback).
+  // |dump_thread_| might be destroyed before getting this point.
+  // It means that tracing was disabled a moment ago.

[Primiano Tucci (use gerrit), 2016/04/13 20:19:16]

s/a moment ago/right before starting this dump/

+  // Anyway either tracing is stopped or this was the last hop, create a trace
+  // event, add it to the trace and finalize process dump (invoke callback).

[Primiano Tucci (use gerrit), 2016/04/13 20:19:16]

s/(invoke callback)/, invoking the callback/

+  if (!pmd_async_state->dump_thread_task_runner.get()) {
+    pmd_async_state->dump_successful = false;
+    pmd_async_state->pending_dump_providers.clear();
+  }
   if (pmd_async_state->pending_dump_providers.empty())
     return FinalizeDumpAndAddToTrace(std::move(pmd_async_state));
 
@@ -418,20 +424,11 @@ void MemoryDumpManager::SetupNextMemoryDump(
       pmd_async_state->pending_dump_providers.back().get();
 
   // If the dump provider did not specify a task runner affinity, dump on
-  // |dump_thread_|. Note that |dump_thread_| might have been destroyed
-  // meanwhile.
+  // |dump_thread_| which is already checked above for presence.
   SequencedTaskRunner* task_runner = mdpinfo->task_runner.get();
   if (!task_runner) {
     DCHECK(mdpinfo->options.dumps_on_single_thread_task_runner);
     task_runner = pmd_async_state->dump_thread_task_runner.get();

[bashi, 2016/04/13 23:39:01]

DCHECK(task_runner) ?

-    if (!task_runner) {
-      // If tracing was disabled before reaching CreateProcessDump() the
-      // dump_thread_ would have been already torn down. Nack current dump and
-      // continue.
-      pmd_async_state->dump_successful = false;
-      pmd_async_state->pending_dump_providers.pop_back();
-      return SetupNextMemoryDump(std::move(pmd_async_state));
-    }
   }
 
   if (mdpinfo->options.dumps_on_single_thread_task_runner &&