Fix race when frees after main thread finishes.

When the main thread is exiting, the code deleted the g_debug global
pointer and destroys the disable pthread key. Unfortunately, if
malloc debug was enabled in a way that requires a header for the pointer,
any frees that occur after the main thread is torn down result in calls
to the underlying allocator with bad pointers.
To avoid this, don't delete the g_debug pointer and don't destroy the
disable pthread key.

Added a new system test that allocates a lot of pointers and frees them
after letting the main thread finish.

Also, fix one test that can fail sporadically due to a lack of unwinding
information on arm32.

Bug: 189541929

Test: Passes new system tests.
Change-Id: I1cfe868987a8f0dc880a5b65de6709f44a5f1988
Merged-In: I1cfe868987a8f0dc880a5b65de6709f44a5f1988
(cherry picked from commit 33d73379aad3ed7dcbb9b10f945d3bc6264b79bd)

1 files changed, 3 insertions, 4 deletions

diff --git a/libc/malloc_debug/malloc_debug.cpp b/libc/malloc_debug/malloc_debug.cpp
index 609f030bf..d23ab15c3 100644
--- a/libc/malloc_debug/malloc_debug.cpp
+++ b/libc/malloc_debug/malloc_debug.cpp
@@ -362,10 +362,9 @@ void debug_finalize() {
 
   backtrace_shutdown();
 
-  delete g_debug;
-  g_debug = nullptr;
-
-  DebugDisableFinalize();
+  // In order to prevent any issues of threads freeing previous pointers
+  // after the main thread calls this code, simply leak the g_debug pointer
+  // and do not destroy the debug disable pthread key.
 }
 
 void debug_get_malloc_leak_info(uint8_t** info, size_t* overall_size, size_t* info_size,