Special case the suspend to runnable transition when locking.

The runtime may be shutting down in parallel, and for daemons that
could lead to failed locking assertions.

bug:27378067
Change-Id: I53785cad537a3d4846661a7b0780543226ea3928

2 files changed, 17 insertions, 2 deletions

diff --git a/runtime/base/mutex-inl.h b/runtime/base/mutex-inl.h
index bd8de877e0..1c320243dc 100644
--- a/runtime/base/mutex-inl.h
+++ b/runtime/base/mutex-inl.h
@@ -73,6 +73,11 @@ static inline void CheckUnattachedThread(LockLevel level) NO_THREAD_SAFETY_ANALY
           level == kThreadListLock ||
           // Ignore logging which may or may not have set up thread data structures.
           level == kLoggingLock ||
+          // When transitioning from suspended to runnable, a daemon thread might be in
+          // a situation where the runtime is shutting down. To not crash our debug locking
+          // mechanism we just pass null Thread* to the MutexLock during that transition
+          // (see Thread::TransitionFromSuspendedToRunnable).
+          level == kThreadSuspendCountLock ||
           // Avoid recursive death.
           level == kAbortLock) << level;
   }
diff --git a/runtime/thread-inl.h b/runtime/thread-inl.h
index d98f82a541..3fd66a7bcb 100644
--- a/runtime/thread-inl.h
+++ b/runtime/thread-inl.h
@@ -201,12 +201,22 @@ inline ThreadState Thread::TransitionFromSuspendedToRunnable() {
                  << " state=" << old_state_and_flags.as_struct.state;
     } else if ((old_state_and_flags.as_struct.flags & kSuspendRequest) != 0) {
       // Wait while our suspend count is non-zero.
-      MutexLock mu(this, *Locks::thread_suspend_count_lock_);
+
+      // We pass null to the MutexLock as we may be in a situation where the
+      // runtime is shutting down. Guarding ourselves from that situation
+      // requires to take the shutdown lock, which is undesirable here.
+      Thread* thread_to_pass = nullptr;
+      if (kIsDebugBuild && !IsDaemon()) {
+        // We know we can make our debug locking checks on non-daemon threads,
+        // so re-enable them on debug builds.
+        thread_to_pass = this;
+      }
+      MutexLock mu(thread_to_pass, *Locks::thread_suspend_count_lock_);
       old_state_and_flags.as_int = tls32_.state_and_flags.as_int;
       DCHECK_EQ(old_state_and_flags.as_struct.state, old_state);
       while ((old_state_and_flags.as_struct.flags & kSuspendRequest) != 0) {
         // Re-check when Thread::resume_cond_ is notified.
-        Thread::resume_cond_->Wait(this);
+        Thread::resume_cond_->Wait(thread_to_pass);
         old_state_and_flags.as_int = tls32_.state_and_flags.as_int;
         DCHECK_EQ(old_state_and_flags.as_struct.state, old_state);
       }