commit 825e82972fe46fdb0419c42bd7df102df1989ff9
author Hans Boehm <hboehm@google.com> Mon Aug 02 17:12:29 2021 -0700
committer Treehugger Robot <treehugger-gerrit@google.com> Sat Aug 07 01:03:51 2021 +0000
tree 9f81ffa70d28a9021209bf508a052023e7495e2a
parent 2d2a27fe91e0a5bb2a047b472ef8d5de9c5a6c73

Make ClassLinker::DumpForSigQuit exclude gc

Otherwise we can get into a deadlock because we hold a critical lock
while waiting for weak reference access, thus potentially preventing
other threads from suspending properly to reenable weak reference
access.

Bug: 195261575
Test: TreeHugger
Change-Id: Ideb6199f597c4e06741c79bb2812661d88a42669

runtime/class_linker.cc

diff --git a/runtime/class_linker.cc b/runtime/class_linker.cc
index 5e6ae1a..43cc365 100644
--- a/runtime/class_linker.cc
+++ b/runtime/class_linker.cc
@@ -9718,16 +9718,22 @@
 }
 
 void ClassLinker::DumpForSigQuit(std::ostream& os) {
-  ScopedObjectAccess soa(Thread::Current());
-  ReaderMutexLock mu(soa.Self(), *Locks::classlinker_classes_lock_);
+  // Avoid a deadlock between a garbage collecting thread running a checkpoint,
+  // a thread holding the dex or classlinker lock and blocking on a condition variable for
+  // weak references access, and a thread blocking on the dex or classlinker lock and thus
+  // unable to run the checkpoint.
+  Thread* self = Thread::Current();
+  ScopedObjectAccess soa(self);
+  gc::ScopedGCCriticalSection gcs(self, gc::kGcCauseClassLinker, gc::kCollectorTypeClassLinker);
+  ReaderMutexLock mu(self, *Locks::classlinker_classes_lock_);
   os << "Zygote loaded classes=" << NumZygoteClasses() << " post zygote classes="
      << NumNonZygoteClasses() << "\n";
-  ReaderMutexLock mu2(soa.Self(), *Locks::dex_lock_);
+  ReaderMutexLock mu2(self, *Locks::dex_lock_);
   os << "Dumping registered class loaders\n";
   size_t class_loader_index = 0;
   for (const ClassLoaderData& class_loader : class_loaders_) {
     ObjPtr<mirror::ClassLoader> loader =
-        ObjPtr<mirror::ClassLoader>::DownCast(soa.Self()->DecodeJObject(class_loader.weak_root));
+        ObjPtr<mirror::ClassLoader>::DownCast(self->DecodeJObject(class_loader.weak_root));
     if (loader != nullptr) {
       os << "#" << class_loader_index++ << " " << loader->GetClass()->PrettyDescriptor() << ": [";
       bool saw_one_dex_file = false;
@@ -9746,7 +9752,7 @@
         size_t parent_index = 0;
         for (const ClassLoaderData& class_loader2 : class_loaders_) {
           ObjPtr<mirror::ClassLoader> loader2 = ObjPtr<mirror::ClassLoader>::DownCast(
-              soa.Self()->DecodeJObject(class_loader2.weak_root));
+              self->DecodeJObject(class_loader2.weak_root));
           if (loader2 == loader->GetParent()) {
             os << ", parent #" << parent_index;
             found_parent = true;