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

[via llvm-commits]

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

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.

>From 249c31365923a67ac0015df1489965de9cf41b09 Mon Sep 17 00:00:00 2001
From: Leonard Chan <leonardchan at google.com>
Date: Tue, 9 Apr 2024 11:50:49 -0700
Subject: [PATCH] [compiler-rt][asan] Fix for flaky asan check

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.
---
 compiler-rt/lib/asan/asan_thread.cpp | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

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() {