commit db440a92e1e337958b6eebdb3c55fbe843e6269c
author Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com> Thu Mar 29 14:38:21 2018 +0100
committer Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com> Fri Jul 13 15:38:20 2018 +0100
tree da851a6e85594484a2ce2a66607e13cff25575fc
parent b46b930e54a54bad0926efb4c36688feaa54764e

drm_hwcomposer: Fix race in ApplyFrame

ApplyFrame holds the lock just when it swaps the value of
active_composition_, in a multithread context we could end up in a
situation where something is shown on the screen, but something else
is set in active_composition_. Fix it by holding the lock during
CommitFrame.

Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>

drmdisplaycompositor.cpp

diff --git a/drmdisplaycompositor.cpp b/drmdisplaycompositor.cpp
index 7276bb5..05832cb 100644
--- a/drmdisplaycompositor.cpp
+++ b/drmdisplaycompositor.cpp
@@ -431,11 +431,6 @@
 }
 
 void DrmDisplayCompositor::ClearDisplay() {
-  AutoLock lock(&lock_, "compositor");
-  int ret = lock.Lock();
-  if (ret)
-    return;
-
   if (!active_composition_)
     return;
 
@@ -447,6 +442,9 @@
 
 void DrmDisplayCompositor::ApplyFrame(
     std::unique_ptr<DrmDisplayComposition> composition, int status) {
+  AutoLock lock(&lock_, __func__);
+  if (lock.Lock())
+    return;
   int ret = status;
 
   if (!ret)
@@ -461,16 +459,8 @@
   }
   ++dump_frames_composited_;
 
-  ret = pthread_mutex_lock(&lock_);
-  if (ret)
-    ALOGE("Failed to acquire lock for active_composition swap");
-
   active_composition_.swap(composition);
 
-  if (!ret)
-    ret = pthread_mutex_unlock(&lock_);
-  if (ret)
-    ALOGE("Failed to release lock for active_composition swap");
 }
 
 int DrmDisplayCompositor::ApplyComposition(