[PATCH] D74567: [scudo][standalone] Workaround for full regions on Android

[Kostya Kortchinsky via Phabricator via llvm-commits]

cryptoad updated this revision to Diff 244485.
cryptoad added a comment.

Adding the test here rather than later.
This made me realize that since the `SizeClassAllocator64` is used on 32-bit
(region size permitting), the `SCUDO_CAN_USE_PRIMARY64` check can't be applied.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74567/new/

https://reviews.llvm.org/D74567

Files:
  compiler-rt/lib/scudo/standalone/combined.h
  compiler-rt/lib/scudo/standalone/tests/combined_test.cpp


Index: compiler-rt/lib/scudo/standalone/tests/combined_test.cpp
===================================================================
--- compiler-rt/lib/scudo/standalone/tests/combined_test.cpp
+++ compiler-rt/lib/scudo/standalone/tests/combined_test.cpp
@@ -344,7 +344,6 @@
 #endif
 }
 
-
 struct DeathSizeClassConfig {
   static const scudo::uptr NumBits = 1;
   static const scudo::uptr MinSizeLog = 10;
@@ -354,10 +353,12 @@
   static const scudo::uptr MaxBytesCachedLog = 10;
 };
 
+static const scudo::uptr DeathRegionSizeLog = 20U;
 struct DeathConfig {
-  // Tiny allocator, its Primary only serves chunks of 1024 bytes.
+  // Tiny allocator, its Primary only serves chunks of two sizes.
   using DeathSizeClassMap = scudo::FixedSizeClassMap<DeathSizeClassConfig>;
-  typedef scudo::SizeClassAllocator64<DeathSizeClassMap, 20U> Primary;
+  typedef scudo::SizeClassAllocator64<DeathSizeClassMap, DeathRegionSizeLog>
+      Primary;
   typedef scudo::MapAllocator<scudo::MapAllocatorNoCache> Secondary;
   template <class A> using TSDRegistryT = scudo::TSDRegistrySharedT<A, 1U>;
 };
@@ -415,3 +416,39 @@
 
   Allocator->releaseToOS();
 }
+
+// Verify that when a region gets full, Android will still manage to
+// fulfill the allocation through a larger size class.
+TEST(ScudoCombinedTest, FullRegion) {
+  using AllocatorT = scudo::Allocator<DeathConfig>;
+  auto Deleter = [](AllocatorT *A) {
+    A->unmapTestOnly();
+    delete A;
+  };
+  std::unique_ptr<AllocatorT, decltype(Deleter)> Allocator(new AllocatorT,
+                                                           Deleter);
+  Allocator->reset();
+
+  const scudo::uptr Size = 1000U;
+  const scudo::uptr MaxNumberOfChunks =
+      (1U << DeathRegionSizeLog) /
+      DeathConfig::DeathSizeClassMap::getSizeByClassId(1U);
+  void *P;
+  std::vector<void *> V;
+  scudo::uptr FailedAllocationsCount = 0;
+  for (scudo::uptr I = 0; I <= MaxNumberOfChunks; I++) {
+    P = Allocator->allocate(Size, Origin);
+    if (!P)
+      FailedAllocationsCount++;
+    else
+      V.push_back(P);
+  }
+  while (!V.empty()) {
+    Allocator->deallocate(V.back(), Origin);
+    V.pop_back();
+  }
+  if (SCUDO_ANDROID)
+    EXPECT_EQ(FailedAllocationsCount, 0U);
+  else
+    EXPECT_GT(FailedAllocationsCount, 0U);
+}
Index: compiler-rt/lib/scudo/standalone/combined.h
===================================================================
--- compiler-rt/lib/scudo/standalone/combined.h
+++ compiler-rt/lib/scudo/standalone/combined.h
@@ -267,6 +267,17 @@
       bool UnlockRequired;
       auto *TSD = TSDRegistry.getTSDAndLock(&UnlockRequired);
       Block = TSD->Cache.allocate(ClassId);
+      // If the allocation failed, the most likely reason with a 64-bit primary
+      // is the region being full. In that event, retry once using the
+      // immediately larger class (except if the failing class was already the
+      // largest). This will waste some memory but will allow the application to
+      // not fail.
+      if (SCUDO_ANDROID) {
+        if (UNLIKELY(!Block)) {
+          if (ClassId < SizeClassMap::LargestClassId)
+            Block = TSD->Cache.allocate(++ClassId);
+        }
+      }
       if (UnlockRequired)
         TSD->unlock();
     } else {


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