[GWP-ASan] Fix atfork handlers being installed multiple times in tests

[hctim]

Summary

We incorrectly install the atfork handlers multiple times in the test
harness, tracked down to the default parameter used by
CheckLateInitIsOK. This manifested in a hang if running the tests with
--gtest_repeat={>=2} as the atfork handler ran multiple times, causing
double-lock and double-unlock, which on my machine hung.

Add a check-fail for this case as well to prevent this from happening
again (it was difficult to track down and is an easy mistake to make).

[hctim]

Rebased. vitalybuka@ / eugenis@ PTAL.

[vitalybuka]

compiler-rt/lib/gwp_asan/platform_specific/guarded_pool_allocator_posix.cpp

101

I would prefer just return instead of CHECK here?

109–110

or even better this way if function local statics are supported

compiler-rt/lib/gwp_asan/tests/late_init.cpp

22 ↗

(On Diff #486071)

then you don't need this change

[hctim]

compiler-rt/lib/gwp_asan/platform_specific/guarded_pool_allocator_posix.cpp

109–110

neat, missed this trick :)

[hctim]

update w/ vitaly's suggestions

[hctim]

yeah, unfortunately no bueno on the "run only once by assigning to a static var" method. It requires cxa guards for static initialization, and we don't link against a cxx runtime. Falling back to the less pretty method.

compiler-rt/lib/gwp_asan/platform_specific/guarded_pool_allocator_posix.cpp

void GuardedPoolAllocator::deallocateInGuardedPool(void *Ptr,
   MaybeSetMappingName(Ptr, Size, kGwpAsanGuardPageName);
 }
 
 size_t GuardedPoolAllocator::getPlatformPageSize() {
   return sysconf(_SC_PAGESIZE);
 }
 
 void GuardedPoolAllocator::installAtFork() {
   auto Disable = []() {
     if (auto *S = getSingleton())
       S->disable();
   };
   auto Enable = []() {
     if (auto *S = getSingleton())
       S->enable();
   };
-  pthread_atfork(Disable, Enable, Enable);
+  static int Done = pthread_atfork(Disable, Enable, Enable);
+  (void)Done;
 }
 } // namespace gwp_asan