Github user vanzin commented on a diff in the pull request:
https://github.com/apache/spark/pull/20191#discussion_r160295529
--- Diff:
common/unsafe/src/main/java/org/apache/spark/unsafe/memory/UnsafeMemoryAllocator.java
---
@@ -38,9 +38,20 @@ public MemoryBlock allocate(long size) throws
OutOfMemoryError {
public void free(MemoryBlock memory) {
assert (memory.obj == null) :
"baseObject not null; are you trying to use the off-heap allocator
to free on-heap memory?";
+ assert (memory.pageNumber !=
MemoryBlock.FREED_IN_ALLOCATOR_PAGE_NUMBER) :
+ "page has already been freed";
+ assert ((memory.pageNumber == MemoryBlock.NO_PAGE_NUMBER)
+ || (memory.pageNumber ==
MemoryBlock.FREED_IN_TMM_PAGE_NUMBER)) :
+ "TMM-allocated pages must be freed via TMM.freePage(), not directly
in allocator free()";
+
if (MemoryAllocator.MEMORY_DEBUG_FILL_ENABLED) {
memory.fill(MemoryAllocator.MEMORY_DEBUG_FILL_FREED_VALUE);
}
Platform.freeMemory(memory.offset);
+ // As an additional layer of defense against use-after-free bugs, we
mutate the
+ // MemoryBlock to reset its pointer.
+ memory.offset = 0;
--- End diff --
Out of curiosity, what's the failure mode if this block is used after free?
SIGSEGV or exception?
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