[hwasan] Improve support of forking with threads (llvm#75291)

Lock Lsan and Thread related date at_fork.

Clean shadow before thread starts, forked process may reuse already
mapped stack of 'lost' parent thread for new threads.

compiler-rt/lib/hwasan/hwasan_linux.cpp

@@ -523,12 +523,24 @@ uptr TagMemoryAligned(uptr p, uptr size, tag_t tag) {
 
 void HwasanInstallAtForkHandler() {
   auto before = []() {
-    HwasanAllocatorLock();
+    if (CAN_SANITIZE_LEAKS) {
+      __lsan::LockGlobal();
+    }
+    // `_lsan` functions defined regardless of `CAN_SANITIZE_LEAKS` and lock the
+    // stuff we need.
+    __lsan::LockThreads();
+    __lsan::LockAllocator();
     StackDepotLockAll();
   };
   auto after = []() {
     StackDepotUnlockAll();
-    HwasanAllocatorUnlock();
+    // `_lsan` functions defined regardless of `CAN_SANITIZE_LEAKS` and unlock
+    // the stuff we need.
+    __lsan::UnlockAllocator();
+    __lsan::UnlockThreads();
+    if (CAN_SANITIZE_LEAKS) {
+      __lsan::UnlockGlobal();
+    }
   };
   pthread_atfork(before, after, after);
 }

compiler-rt/lib/hwasan/hwasan_thread.cpp

@@ -68,6 +68,7 @@ void Thread::Init(uptr stack_buffer_start, uptr stack_buffer_size,
     }
     Print("Creating  : ");
   }
+  ClearShadowForThreadStackAndTLS();
 }
 
 void Thread::InitStackRingBuffer(uptr stack_buffer_start,

compiler-rt/test/sanitizer_common/TestCases/Posix/fork_threaded.c

@@ -1,7 +1,5 @@
 // RUN: %clang -O0 %s -o %t && %env_tool_opts=die_after_fork=0 %run %t
 
-// UNSUPPORTED: hwasan
-
 // The test uses pthread barriers which are not available on Darwin.
 // UNSUPPORTED: darwin