[XRay][ARM32][AArch64] Fix unstable FDR tests on weak-ordering CPUs

[rSerge]

Summary

Change from compare_exchange_weak() to compare_exchange_strong() where appropriate, because on ARM ( http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15-full/builds/3190 , http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15-full/builds/3191 ) and AArch64 ( http://lab.llvm.org:8011/builders/clang-cmake-aarch64-42vma/builds/3900 ) it fails even in single-threaded scenarios.

[rengolin]

I'm accepting this in light of the comments in the thread http://lists.llvm.org/pipermail/llvm-dev/2017-January/109524.html

If there is any problem or a better implementation, we can revert and re-implement later. Right now getting the bots stable again is priority.

cheers,
--renato

[rSerge]

@rengolin , I think your link to the mailing list is wrong. Here is the correct one: https://groups.google.com/forum/#!topic/llvm-dev/2Lt6DEZLgmo

[rSerge]

Reached mainline in revision 293505.

[rengolin]

In D29286#660551, @rSerge wrote:

@rengolin , I think your link to the mailing list is wrong. Here is the correct one: https://groups.google.com/forum/#!topic/llvm-dev/2Lt6DEZLgmo

Dang! Sorry!

lib/xray/xray_fdr_logging.cc

 
 std::unique_ptr<FDRLoggingOptions> FDROptions;
 
 XRayLogInitStatus FDRLogging_init(std::size_t BufferSize, std::size_t BufferMax,
                                   void *Options,
                                   size_t OptionsSize) XRAY_NEVER_INSTRUMENT {
   assert(OptionsSize == sizeof(FDRLoggingOptions));
   XRayLogInitStatus CurrentStatus = XRayLogInitStatus::XRAY_LOG_UNINITIALIZED;
-  if (!LoggingStatus.compare_exchange_weak(
+  if (!LoggingStatus.compare_exchange_strong(
           CurrentStatus, XRayLogInitStatus::XRAY_LOG_INITIALIZING,
           std::memory_order_release, std::memory_order_relaxed))
     return CurrentStatus;
 
   FDROptions.reset(new FDRLoggingOptions());
   *FDROptions = *reinterpret_cast<FDRLoggingOptions *>(Options);
   if (FDROptions->ReportErrors)
     SetPrintfAndReportCallback(PrintToStdErr);

 
 // Must finalize before flushing.
 XRayLogFlushStatus FDRLogging_flush() XRAY_NEVER_INSTRUMENT {
   if (LoggingStatus.load(std::memory_order_acquire) !=
       XRayLogInitStatus::XRAY_LOG_FINALIZED)
     return XRayLogFlushStatus::XRAY_LOG_NOT_FLUSHING;
 
   XRayLogFlushStatus Result = XRayLogFlushStatus::XRAY_LOG_NOT_FLUSHING;
-  if (!LogFlushStatus.compare_exchange_weak(
+  if (!LogFlushStatus.compare_exchange_strong(
           Result, XRayLogFlushStatus::XRAY_LOG_FLUSHING,
           std::memory_order_release, std::memory_order_relaxed))
     return Result;
 
   // Make a copy of the BufferQueue pointer to prevent other threads that may be
   // resetting it from blowing away the queue prematurely while we're dealing
   // with it.
   auto LocalBQ = BQ;
XRayLogFlushStatus FDRLogging_flush() XRAY_NEVER_INSTRUMENT {
   });
   LogFlushStatus.store(XRayLogFlushStatus::XRAY_LOG_FLUSHED,
                        std::memory_order_release);
   return XRayLogFlushStatus::XRAY_LOG_FLUSHED;
 }
 
 XRayLogInitStatus FDRLogging_finalize() XRAY_NEVER_INSTRUMENT {
   XRayLogInitStatus CurrentStatus = XRayLogInitStatus::XRAY_LOG_INITIALIZED;
-  if (!LoggingStatus.compare_exchange_weak(
+  if (!LoggingStatus.compare_exchange_strong(
           CurrentStatus, XRayLogInitStatus::XRAY_LOG_FINALIZING,
           std::memory_order_release, std::memory_order_relaxed))
     return CurrentStatus;
 
   // Do special things to make the log finalize itself, and not allow any more
   // operations to be performed until re-initialized.
   BQ->finalize();
 
   LoggingStatus.store(XRayLogInitStatus::XRAY_LOG_FINALIZED,
                       std::memory_order_release);
   return XRayLogInitStatus::XRAY_LOG_FINALIZED;
 }
 
 XRayLogInitStatus FDRLogging_reset() XRAY_NEVER_INSTRUMENT {
   XRayLogInitStatus CurrentStatus = XRayLogInitStatus::XRAY_LOG_FINALIZED;
-  if (!LoggingStatus.compare_exchange_weak(
+  if (!LoggingStatus.compare_exchange_strong(
           CurrentStatus, XRayLogInitStatus::XRAY_LOG_UNINITIALIZED,
           std::memory_order_release, std::memory_order_relaxed))
     return CurrentStatus;
 
   // Release the in-memory buffer queue.
   BQ.reset();
 
   // Spin until the flushing status is flushed.