[PATCH] D58940: [Sanitizer] Only unwind when it is safe to do so

[Julian Lettner via Phabricator via llvm-commits]

yln created this revision.
yln added a reviewer: vitalybuka.
Herald added subscribers: llvm-commits, Sanitizers, kubamracek.
Herald added projects: Sanitizers, LLVM.

ScopedUnwinding and AsanThread::isUnwinding were introduced to

> "Fix deadlock in stack unwinder on android/x86" on platforms where
>  libc unwinder calls malloc internally.

https://github.com/llvm/llvm-project/commit/58dbe0623051f1bb49256693e54b4e29f7db5faf

The current state of the code only protects the fast unwinder, which is
not affected by this. Only SlowUnwind calls out to `_Unwind_Backtrace`.
So we are in a situation where the code that should be protected isn't,
and code that doesn't need to be protected is.

Since this hasn't been causing issues, we don't even know if it strictly
required anymore. But let's be conservative and make sure at least also
SlowUnwind is protected.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D58940

Files:
  compiler-rt/lib/asan/asan_stack.cc


Index: compiler-rt/lib/asan/asan_stack.cc
===================================================================
--- compiler-rt/lib/asan/asan_stack.cc
+++ compiler-rt/lib/asan/asan_stack.cc
@@ -35,10 +35,12 @@
   if (UNLIKELY(!asan_inited)) return;
 
   AsanThread *t = GetCurrentThread();
-  if (t && !t->isUnwinding() && WillUseFastUnwind(request_fast)) {
+  if (!t || t->isUnwinding()) return;
+
+  ScopedUnwinding unwind_scope(t);
+  if (WillUseFastUnwind(request_fast)) {
     uptr top = t->stack_top();
     uptr bottom = t->stack_bottom();
-    ScopedUnwinding unwind_scope(t);
     if (!SANITIZER_MIPS || IsValidFrame(bp, top, bottom)) {
       UnwindFast(pc, bp, top, bottom, max_depth);
       return;


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