Short circuit free(nullptr).

This is needed to prevent a crash that happens when we enable heapprof
while Bionic atrace is also enabled.

Cherry-pick of c3a91a37e4503eb6537a81c3a17ee3187ae196b7

Bug: 137284735

Test: flash walleye-userdebug
      profile system_server and concurrently run bionic atrace

Change-Id: Ia123a17b7df0790cb82c6c9073ce5638cd1a189f
Merged-In: Ia123a17b7df0790cb82c6c9073ce5638cd1a189f

1 files changed, 11 insertions, 0 deletions

diff --git a/src/profiling/memory/malloc_hooks.cc b/src/profiling/memory/malloc_hooks.cc
index 6070a03cb..387fd842d 100644
--- a/src/profiling/memory/malloc_hooks.cc
+++ b/src/profiling/memory/malloc_hooks.cc
@@ -501,6 +501,17 @@ int HEAPPROFD_ADD_PREFIX(_posix_memalign)(void** memptr,
 // sure that the address is not reused before we've processed the deallocation
 // (which includes assigning a sequence id to it).
 void HEAPPROFD_ADD_PREFIX(_free)(void* pointer) {
+  // free on a nullptr is valid but has no effect. Short circuit here, for
+  // various advantages:
+  // * More efficient
+  // * Notably printf calls free(nullptr) even when it is used in a way
+  //   malloc-free way, as it unconditionally frees the pointer even if
+  //   it was never written to.
+  //   Short circuiting here makes it less likely to accidentally build
+  //   infinite recursion.
+  if (pointer == nullptr)
+    return;
+
   const MallocDispatch* dispatch = GetDispatch();
   std::shared_ptr<perfetto::profiling::Client> client;
   {