commit bb2ec6a4a9cbc4f39819723ba48be404a5443296
author Melody Hsu <melodymhsu@google.com> Mon May 27 22:18:05 2024 +0000
committer Melody Hsu <melodymhsu@google.com> Tue May 28 19:54:53 2024 +0000
tree 16253036e58c8e9eadb05a9f1831812e53949e8d
parent 81afac912242a9914f2e7edc290f7e346e96e148

Log detected cycles in LayerHierarchy#traverse

Prevents a stack overflow in the event of a cyclic
hierarchy.

Fixes: b/341182047
Test: atest SurfaceFlinger_test
Change-Id: I930cda6258cdabe0bdc98bd68bdd88f1de7c1a8c

services/surfaceflinger/FrontEnd/LayerHierarchy.cpp

diff --git a/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp b/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp
index 0dcbb3c..2b20de3 100644
--- a/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp
+++ b/services/surfaceflinger/FrontEnd/LayerHierarchy.cpp
@@ -52,8 +52,12 @@
     mChildren = hierarchy.mChildren;
 }
 
-void LayerHierarchy::traverse(const Visitor& visitor,
-                              LayerHierarchy::TraversalPath& traversalPath) const {
+void LayerHierarchy::traverse(const Visitor& visitor, LayerHierarchy::TraversalPath& traversalPath,
+                              uint32_t depth) const {
+    LLOG_ALWAYS_FATAL_WITH_TRACE_IF(depth > 50,
+                                    "Cycle detected in LayerHierarchy::traverse. See "
+                                    "traverse_stack_overflow_transactions.winscope");
+
     if (mLayer) {
         bool breakTraversal = !visitor(*this, traversalPath);
         if (breakTraversal) {
@@ -66,7 +70,7 @@
     for (auto& [child, childVariant] : mChildren) {
         ScopedAddToTraversalPath addChildToTraversalPath(traversalPath, child->mLayer->id,
                                                          childVariant);
-        child->traverse(visitor, traversalPath);
+        child->traverse(visitor, traversalPath, depth + 1);
     }
 }
 

services/surfaceflinger/FrontEnd/LayerHierarchy.h

diff --git a/services/surfaceflinger/FrontEnd/LayerHierarchy.h b/services/surfaceflinger/FrontEnd/LayerHierarchy.h
index f62e758..69710be 100644
--- a/services/surfaceflinger/FrontEnd/LayerHierarchy.h
+++ b/services/surfaceflinger/FrontEnd/LayerHierarchy.h
@@ -147,7 +147,7 @@
         if (mLayer) {
             root.id = mLayer->id;
         }
-        traverse(visitor, root);
+        traverse(visitor, root, /*depth=*/0);
     }
 
     // Traverse the hierarchy in z-order, skipping children that have relative parents.
@@ -190,7 +190,8 @@
     void sortChildrenByZOrder();
     void updateChild(LayerHierarchy*, LayerHierarchy::Variant);
     void traverseInZOrder(const Visitor& visitor, LayerHierarchy::TraversalPath& parent) const;
-    void traverse(const Visitor& visitor, LayerHierarchy::TraversalPath& parent) const;
+    void traverse(const Visitor& visitor, LayerHierarchy::TraversalPath& parent,
+                  uint32_t depth = 0) const;
     void dump(std::ostream& out, const std::string& prefix, LayerHierarchy::Variant variant,
               bool isLastChild, bool includeMirroredHierarchy) const;