Avoid suspending heap task thread for getting stack traces

Instead of suspending the heap task thread, GetThreadStack (called by
VMStack_fillStackTraceElements and VMStack_getThreadStackTrace) will
return an empty thread stack. This fixes possible deadlocks caused by
suspending the GC thread and doing allocations for the stack trace.

Bug: 28261069

Test: test-art-host

Change-Id: I45a0b8ac94a99d6bbcfcdc2b41afadf941ec0138

1 files changed, 11 insertions, 1 deletions

diff --git a/runtime/native/dalvik_system_VMStack.cc b/runtime/native/dalvik_system_VMStack.cc
index 36825cb870..268d71ac65 100644
--- a/runtime/native/dalvik_system_VMStack.cc
+++ b/runtime/native/dalvik_system_VMStack.cc
@@ -17,6 +17,7 @@
 #include "dalvik_system_VMStack.h"
 
 #include "art_method-inl.h"
+#include "gc/task_processor.h"
 #include "jni_internal.h"
 #include "nth_caller_visitor.h"
 #include "mirror/class-inl.h"
@@ -31,9 +32,18 @@ namespace art {
 static jobject GetThreadStack(const ScopedFastNativeObjectAccess& soa, jobject peer)
     REQUIRES_SHARED(Locks::mutator_lock_) {
   jobject trace = nullptr;
-  if (soa.Decode<mirror::Object>(peer) == soa.Self()->GetPeer()) {
+  ObjPtr<mirror::Object> decoded_peer = soa.Decode<mirror::Object>(peer);
+  if (decoded_peer == soa.Self()->GetPeer()) {
     trace = soa.Self()->CreateInternalStackTrace<false>(soa);
   } else {
+    // Never allow suspending the heap task thread since it may deadlock if allocations are
+    // required for the stack trace.
+    Thread* heap_task_thread =
+        Runtime::Current()->GetHeap()->GetTaskProcessor()->GetRunningThread();
+    // heap_task_thread could be null if the daemons aren't yet started.
+    if (heap_task_thread != nullptr && decoded_peer == heap_task_thread->GetPeer()) {
+      return nullptr;
+    }
     // Suspend thread to build stack trace.
     ScopedThreadSuspension sts(soa.Self(), kNative);
     ThreadList* thread_list = Runtime::Current()->GetThreadList();