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

[via llvm-commits]

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

>From 3123d1590a99142b6c3d3653c7f4792b05f213d4 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 | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/compiler-rt/lib/asan/asan_thread.cpp b/compiler-rt/lib/asan/asan_thread.cpp
index 8798968947e82e..480a423952e8f3 100644
--- a/compiler-rt/lib/asan/asan_thread.cpp
+++ b/compiler-rt/lib/asan/asan_thread.cpp
@@ -44,10 +44,15 @@ static ThreadRegistry *asan_thread_registry;
 static ThreadArgRetval *thread_data;
 
 static Mutex mu_for_thread_context;
+// TODO(leonardchan@): It should be possible to make LowLevelAllocator
+// threadsafe and consolidate this one into the GlobalLoweLevelAllocator.
+// We should be able to do something similar to what's in
+// sanitizer_stack_store.cpp.
+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() {