[compiler-rt] [compiler-rt][asan] Fix for flaky asan check (PR #88177)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: None (PiJoules)

<details>
<summary>Changes</summary>

This fixes https://github.com/llvm/llvm-project/issues/87324.

We haven't been able to come up with a minimal reproducer but we can reliabely avoid this failure with the following fix. Prior to the GetGlobalLowLevelAllocator change, the old LowLevelAllocator aquired a lock associated with it preventing that specific allocator from being accessed at the same time by many threads. With the GetGlobalLowLevelAllocator change, I had accidentally replaced it but not taken into account the lock, so we can have a data race if the allocator is used at any point while a thread is being created. The global allocator can be used for flag parsing or registering asan globals.

---
Full diff: https://github.com/llvm/llvm-project/pull/88177.diff


1 Files Affected:

- (modified) compiler-rt/lib/asan/asan_thread.cpp (+2-1) 


``````````diff
diff --git a/compiler-rt/lib/asan/asan_thread.cpp b/compiler-rt/lib/asan/asan_thread.cpp
index 8798968947e82e..95aeccd070b551 100644
--- a/compiler-rt/lib/asan/asan_thread.cpp
+++ b/compiler-rt/lib/asan/asan_thread.cpp
@@ -44,10 +44,11 @@ static ThreadRegistry *asan_thread_registry;
 static ThreadArgRetval *thread_data;
 
 static Mutex mu_for_thread_context;
+static LowLevelAllocator allocator_for_thread_context;
 
 static ThreadContextBase *GetAsanThreadContext(u32 tid) {
   Lock lock(&mu_for_thread_context);
-  return new (GetGlobalLowLevelAllocator()) AsanThreadContext(tid);
+  return new (allocator_for_thread_context) AsanThreadContext(tid);
 }
 
 static void InitThreads() {

``````````

</details>


https://github.com/llvm/llvm-project/pull/88177