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/SurfaceFlinger.cpp

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 29fe5d9..3052819 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -4482,12 +4482,11 @@
     result.append("\n");
 }
 
-LayersProto SurfaceFlinger::dumpDrawingStateProto(uint32_t traceFlags) const {
-    Mutex::Autolock _l(mStateLock);
-    const auto device = getDefaultDisplayDeviceLocked();
+LayersProto SurfaceFlinger::dumpDrawingStateProto(
+        uint32_t traceFlags, const sp<const DisplayDevice>& displayDevice) const {
     LayersProto layersProto;
     for (const sp<Layer>& layer : mDrawingState.layersSortedByZ) {
-        layer->writeToProto(layersProto, traceFlags, device);
+        layer->writeToProto(layersProto, traceFlags, displayDevice);
     }
 
     return layersProto;
@@ -4519,7 +4518,10 @@
 
 LayersProto SurfaceFlinger::dumpProtoFromMainThread(uint32_t traceFlags) {
     LayersProto layersProto;
-    postMessageSync(new LambdaMessage([&]() { layersProto = dumpDrawingStateProto(traceFlags); }));
+    postMessageSync(new LambdaMessage([&]() {
+        const auto& displayDevice = getDefaultDisplayDeviceLocked();
+        layersProto = dumpDrawingStateProto(traceFlags, displayDevice);
+    }));
     return layersProto;
 }