Index: compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp
===================================================================
--- compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp
+++ compiler-rt/lib/sanitizer_common/sanitizer_posix_libcdep.cpp
@@ -15,6 +15,7 @@
 
 #if SANITIZER_POSIX
 
+#include "sanitizer_atomic.h"
 #include "sanitizer_common.h"
 #include "sanitizer_flags.h"
 #include "sanitizer_platform_limits_netbsd.h"
@@ -166,9 +167,14 @@
 #if !SANITIZER_GO
 // TODO(glider): different tools may require different altstack size.
 static uptr GetAltStackSize() {
-  // SIGSTKSZ is not enough.
-  static const uptr kAltStackSize = SIGSTKSZ * 4;
-  return kAltStackSize;
+  static atomic_uintptr_t kAltStackSize{0};
+  uptr ret = atomic_load(&kAltStackSize, memory_order_relaxed);
+  if (ret == 0) {
+    // SIGSTKSZ is not enough.
+    ret = SIGSTKSZ * 4;
+    atomic_store(&kAltStackSize, ret, memory_order_relaxed);
+  }
+  return ret;
 }
 
 void SetAlternateSignalStack() {