[PATCH] D51224: [scudo] Replace eraseHeader with compareExchangeHeader for Quarantined chunks

[Kostya Kortchinsky via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rCRT340633: [scudo] Replace eraseHeader with compareExchangeHeader for Quarantined chunks (authored by cryptoad, committed by ).

Changed prior to commit:
  https://reviews.llvm.org/D51224?vs=162411&id=162429#toc

Repository:
  rCRT Compiler Runtime

https://reviews.llvm.org/D51224

Files:
  lib/scudo/scudo_allocator.cpp


Index: lib/scudo/scudo_allocator.cpp
===================================================================
--- lib/scudo/scudo_allocator.cpp
+++ lib/scudo/scudo_allocator.cpp
@@ -129,16 +129,9 @@
             computeChecksum(Ptr, &NewUnpackedHeader));
   }
 
-  // Nulls out a chunk header. When returning the chunk to the backend, there
-  // is no need to store a valid ChunkAvailable header, as this would be
-  // computationally expensive. Zeroing out serves the same purpose by making
-  // the header invalid. In the extremely rare event where 0 would be a valid
-  // checksum for the chunk, the state of the chunk is ChunkAvailable anyway.
+  // Ensure that ChunkAvailable is 0, so that if a 0 checksum is ever valid
+  // for a fully nulled out header, its state will be available anyway.
   COMPILER_CHECK(ChunkAvailable == 0);
-  static INLINE void eraseHeader(void *Ptr) {
-    const PackedHeader NullPackedHeader = 0;
-    atomic_store_relaxed(getAtomicHeader(Ptr), NullPackedHeader);
-  }
 
   // Loads and unpacks the header, verifying the checksum in the process.
   static INLINE
@@ -185,7 +178,9 @@
     Chunk::loadHeader(Ptr, &Header);
     if (UNLIKELY(Header.State != ChunkQuarantine))
       dieWithMessage("invalid chunk state when recycling address %p\n", Ptr);
-    Chunk::eraseHeader(Ptr);
+    UnpackedHeader NewHeader = Header;
+    NewHeader.State = ChunkAvailable;
+    Chunk::compareExchangeHeader(Ptr, &NewHeader, &Header);
     void *BackendPtr = Chunk::getBackendPtr(Ptr, &Header);
     if (Header.ClassId)
       getBackend().deallocatePrimary(Cache_, BackendPtr, Header.ClassId);


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