[vm] Fix deadlocks in shared field initialization.

TEST=ci
Bug: https://github.com/dart-lang/sdk/issues/62392
Change-Id: Id34b7f47c8f03c4cd0fb6555912279ee03303f23
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/474565
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

runtime/vm/heap/safepoint.h

@@ -376,6 +376,30 @@ class TransitionVMToBlocked : public TransitionSafepointState {
   DISALLOW_COPY_AND_ASSIGN(TransitionVMToBlocked);
 };
 
+class TransitionVMToBlockedReloadableStealable
+    : public TransitionSafepointState {
+ public:
+  explicit TransitionVMToBlockedReloadableStealable(Thread* T)
+      : TransitionSafepointState(T) {
+    ASSERT(T->CanAcquireSafepointLocks());
+    // A thread blocked on a monitor is considered to be at a safepoint.
+    ASSERT(T->execution_state() == Thread::kThreadInVM);
+    T->set_execution_state(Thread::kThreadInReloadableBlockedState);
+    T->EnterSafepointToNative();
+  }
+
+  ~TransitionVMToBlockedReloadableStealable() {
+    // We are returning to vm code and so we are not at a safepoint anymore.
+    ASSERT(thread()->execution_state() ==
+           Thread::kThreadInReloadableBlockedState);
+    thread()->ExitSafepointFromNative();
+    thread()->set_execution_state(Thread::kThreadInVM);
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TransitionVMToBlockedReloadableStealable);
+};
+
 // TransitionVMToNative is used to transition the safepoint state of a
 // thread from "running vm code" to "running native code" and ensures
 // that the state is reverted back to "running vm code" when

runtime/vm/lockers.cc

@@ -198,6 +198,32 @@ void SafepointRwLock::EnterWrite() {
   }
 }
 
+void SafepointRwLock::EnterWriteReloadableStealable() {
+  // No need to safepoint if the current thread is not attached.
+  auto thread = Thread::Current();
+  // Attempt to acquire a lock while owning a safepoint could lead to a deadlock
+  // (some other thread might be forced to a safepoint while holding this lock).
+  //
+  // Though if the lock was already acquired by this thread before entering a
+  // safepoint, we do allow the nested acquire (which is a NOP).
+  ASSERT(thread == nullptr || thread->execution_state() == Thread::kThreadInVM);
+  DEBUG_ASSERT(thread == nullptr || thread->CanAcquireSafepointLocks() ||
+               IsCurrentThreadWriter());
+
+  const bool can_block_without_safepoint = thread == nullptr;
+
+  RELEASE_ASSERT(can_block_without_safepoint ||
+                 thread->current_safepoint_level() >=
+                     expected_safepoint_level_);
+
+  if (!TryEnterWrite(can_block_without_safepoint)) {
+    // Important: must never hold monitor_ when blocking for safepoint.
+    TransitionVMToBlockedReloadableStealable transition(thread);
+    const bool ok = TryEnterWrite(/*can_block=*/true);
+    RELEASE_ASSERT(ok);
+  }
+}
+
 bool SafepointRwLock::TryEnterWrite(bool can_block) {
   MonitorLocker ml(&monitor_);
   if (IsCurrentThreadWriter()) {

runtime/vm/lockers.h

@@ -379,6 +379,7 @@ class SafepointRwLock {
  private:
   friend class SafepointReadRwLocker;
   friend class SafepointWriteRwLocker;
+  friend class ReloadableStealableWriteRwLocker;
 
   // returns [true] if read lock was acquired,
   // returns [false] if the thread didn't have to acquire read lock due
@@ -388,6 +389,7 @@ class SafepointRwLock {
   void LeaveRead();
 
   void EnterWrite();
+  void EnterWriteReloadableStealable();
   bool TryEnterWrite(bool can_block);
   void LeaveWrite();
 
@@ -500,6 +502,23 @@ class SafepointWriteRwLocker : public StackResource {
   SafepointRwLock* rw_lock_;
 };
 
+/*
+ * Allows reload safepoint and active mutator slot stealing while blocked.
+ */
+class ReloadableStealableWriteRwLocker : public StackResource {
+ public:
+  ReloadableStealableWriteRwLocker(ThreadState* thread_state,
+                                   SafepointRwLock* rw_lock)
+      : StackResource(thread_state), rw_lock_(rw_lock) {
+    rw_lock_->EnterWriteReloadableStealable();
+  }
+
+  ~ReloadableStealableWriteRwLocker() { rw_lock_->LeaveWrite(); }
+
+ private:
+  SafepointRwLock* rw_lock_;
+};
+
 }  // namespace dart
 
 #endif  // RUNTIME_VM_LOCKERS_H_

runtime/vm/runtime_entry.cc

@@ -5231,7 +5231,11 @@ DEFINE_LEAF_RUNTIME_ENTRY(PropagateError,
                           DLRT_PropagateError);
 
 DEFINE_RUNTIME_ENTRY(InitializeSharedField, 1) {
-  SafepointWriteRwLocker locker(
+  // Running the initializer means running arbitrary Dart code that might yield
+  // to a reload safepoint or have its active mutator slot stolen. Make sure we
+  // likewise yield while waiting for the lock to avoid the holder of the lock
+  // being blocked on locker-waiters for reload or a mutator slot.
+  ReloadableStealableWriteRwLocker locker(
       thread, thread->isolate_group()->shared_field_initializer_rwlock());
   const Field& field = Field::CheckedHandle(zone, arguments.ArgAt(0));
   Object& result = Object::Handle(zone, field.StaticValue());

runtime/vm/thread.h

@@ -1108,7 +1108,8 @@ class Thread : public ThreadState, public IntrusiveDListEntry<Thread> {
     kThreadInVM = 0,
     kThreadInGenerated,
     kThreadInNative,
-    kThreadInBlockedState
+    kThreadInBlockedState,
+    kThreadInReloadableBlockedState
   };
 
   ExecutionState execution_state() const {
@@ -1317,7 +1318,8 @@ class Thread : public ThreadState, public IntrusiveDListEntry<Thread> {
     if (no_reload_scope_depth_ > 0) {
       return SafepointLevel::kGCAndDeopt;
     }
-    if (execution_state_ == kThreadInNative) {
+    if (execution_state_ == kThreadInNative ||
+        execution_state_ == kThreadInReloadableBlockedState) {
       return SafepointLevel::kGCAndDeoptAndReload;
     }
     if (allow_reload_scope_depth_ <= 0) {