commit 5793c7d8d85e25a4226178a96b3b7f81a76da501
author Alec Mouri <alecmouri@google.com> Tue Mar 10 19:55:50 2020 -0700
committer Alec Mouri <alecmouri@google.com> Wed Mar 11 01:20:07 2020 -0700
tree cd303a5c51d15e7bec77038326dc618274f0b35d
parent 8929001832590afd537f2e06147c039b951d862c

[SurfaceFlinger] Resolve deadlock in SurfaceTracing.

SurfaceTracing cannot acquire mStateLock while mDrawingStateLock is
held. SurfaceTracing only needs to acquire mStateLock for getting the
default DisplayDevice for getting a layer's HWC composition type. As a
workaround, grab the DisplayDevice ahead of time.

Bug: 151108871
Test: builds
Change-Id: I84a76694e9890242c666ec5e3eb04d4114f8240a

services/surfaceflinger/SurfaceTracing.cpp

diff --git a/services/surfaceflinger/SurfaceTracing.cpp b/services/surfaceflinger/SurfaceTracing.cpp
index c5556ec..20c8d7a 100644
--- a/services/surfaceflinger/SurfaceTracing.cpp
+++ b/services/surfaceflinger/SurfaceTracing.cpp
@@ -45,19 +45,21 @@
 }
 
 void SurfaceTracing::addFirstEntry() {
+    const auto displayDevice = mFlinger.getDefaultDisplayDevice();
     LayersTraceProto entry;
     {
         std::scoped_lock lock(mSfLock);
-        entry = traceLayersLocked("tracing.enable");
+        entry = traceLayersLocked("tracing.enable", displayDevice);
     }
     addTraceToBuffer(entry);
 }
 
 LayersTraceProto SurfaceTracing::traceWhenNotified() {
+    const auto displayDevice = mFlinger.getDefaultDisplayDevice();
     std::unique_lock<std::mutex> lock(mSfLock);
     mCanStartTrace.wait(lock);
     android::base::ScopedLockAssertion assumeLock(mSfLock);
-    LayersTraceProto entry = traceLayersLocked(mWhere);
+    LayersTraceProto entry = traceLayersLocked(mWhere, displayDevice);
     lock.unlock();
     return entry;
 }
@@ -160,13 +162,14 @@
     mTraceFlags = flags;
 }
 
-LayersTraceProto SurfaceTracing::traceLayersLocked(const char* where) {
+LayersTraceProto SurfaceTracing::traceLayersLocked(const char* where,
+                                                   const sp<const DisplayDevice>& displayDevice) {
     ATRACE_CALL();
 
     LayersTraceProto entry;
     entry.set_elapsed_realtime_nanos(elapsedRealtimeNano());
     entry.set_where(where);
-    LayersProto layers(mFlinger.dumpDrawingStateProto(mTraceFlags));
+    LayersProto layers(mFlinger.dumpDrawingStateProto(mTraceFlags, displayDevice));
     mFlinger.dumpOffscreenLayersProto(layers);
     entry.mutable_layers()->Swap(&layers);