Fix for potential deadlock in EventThread::onNewVsyncSchedule
I haven't seen such a deadlock, but looking over
I86e66df59c64e81c4aa721a25250697f61237488 and the potential deadlock
that inspired it, I think there could be a similar problem in
EventThread. As I understand it, this is partially because of the
fact that EventThread does not unregister the old callback. This is
addressed in I3c1eccb36914f29560600d48bb08b1b8f2fe7c96.
Fix the deadlock with a similar approach as
I86e66df59c64e81c4aa721a25250697f61237488: hold on to the old
registration until after releasing the mutex.
Bug: 279209321
Test: infeasible
Change-Id: If490f88115aa298d31aa9ad392a1f9f9dc987549
diff --git a/services/surfaceflinger/Scheduler/EventThread.cpp b/services/surfaceflinger/Scheduler/EventThread.cpp
index 74665a7..1c0bf0d 100644
--- a/services/surfaceflinger/Scheduler/EventThread.cpp
+++ b/services/surfaceflinger/Scheduler/EventThread.cpp
@@ -692,17 +692,27 @@
}
void EventThread::onNewVsyncSchedule(std::shared_ptr<scheduler::VsyncSchedule> schedule) {
+ // Hold onto the old registration until after releasing the mutex to avoid deadlock.
+ scheduler::VSyncCallbackRegistration oldRegistration =
+ onNewVsyncScheduleInternal(std::move(schedule));
+}
+
+scheduler::VSyncCallbackRegistration EventThread::onNewVsyncScheduleInternal(
+ std::shared_ptr<scheduler::VsyncSchedule> schedule) {
std::lock_guard<std::mutex> lock(mMutex);
const bool reschedule = mVsyncRegistration.cancel() == scheduler::CancelResult::Cancelled;
mVsyncSchedule = std::move(schedule);
- mVsyncRegistration =
- scheduler::VSyncCallbackRegistration(mVsyncSchedule->getDispatch(),
- createDispatchCallback(), mThreadName);
+ auto oldRegistration =
+ std::exchange(mVsyncRegistration,
+ scheduler::VSyncCallbackRegistration(mVsyncSchedule->getDispatch(),
+ createDispatchCallback(),
+ mThreadName));
if (reschedule) {
mVsyncRegistration.schedule({.workDuration = mWorkDuration.get().count(),
.readyDuration = mReadyDuration.count(),
.earliestVsync = mLastVsyncCallbackTime.ns()});
}
+ return oldRegistration;
}
scheduler::VSyncDispatch::Callback EventThread::createDispatchCallback() {