[compiler-rt] r345489 - [XRay] Guard call to postCurrentThreadFCT()

[Dean Michael Berris via llvm-commits]

Author: dberris
Date: Sun Oct 28 22:39:43 2018
New Revision: 345489

URL: http://llvm.org/viewvc/llvm-project?rev=345489&view=rev
Log:
[XRay] Guard call to postCurrentThreadFCT()

Summary:
Some cases where `postCurrentThreadFCT()` are not guarded by our
recursion guard. We've observed that sometimes these can lead to
deadlocks when some functions (like memcpy()) gets outlined and the
version of memcpy is XRay-instrumented, which can be materialised by the
compiler in the implementation of lower-level components used by the
profiling runtime.

This change ensures that all calls to `postCurrentThreadFCT` are guarded
by our thread-recursion guard, to prevent deadlocks.

Reviewers: mboerger, eizan

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D53805

Modified:
    compiler-rt/trunk/lib/xray/xray_profiling.cc

Modified: compiler-rt/trunk/lib/xray/xray_profiling.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/xray/xray_profiling.cc?rev=345489&r1=345488&r2=345489&view=diff
==============================================================================
--- compiler-rt/trunk/lib/xray/xray_profiling.cc (original)
+++ compiler-rt/trunk/lib/xray/xray_profiling.cc Sun Oct 28 22:39:43 2018
@@ -133,7 +133,7 @@ XRayLogFlushStatus profilingFlush() XRAY
       if (Verbosity())
         Report("profiling: No data to flush.\n");
     } else {
-      LogWriter* LW = LogWriter::Open();
+      LogWriter *LW = LogWriter::Open();
       if (LW == nullptr) {
         if (Verbosity())
           Report("profiling: Failed to flush to file, dropping data.\n");
@@ -227,10 +227,15 @@ XRayLogInitStatus profilingFinalize() XR
   // Wait a grace period to allow threads to see that we're finalizing.
   SleepForMillis(profilingFlags()->grace_period_ms);
 
-  // We also want to make sure that the current thread's data is cleaned up,
-  // if we have any.
+  // We also want to make sure that the current thread's data is cleaned up, if
+  // we have any. We need to ensure that the call to postCurrentThreadFCT() is
+  // guarded by our recursion guard.
   auto &TLD = getThreadLocalData();
-  postCurrentThreadFCT(TLD);
+  {
+    RecursionGuard G(ReentranceGuard);
+    if (G)
+      postCurrentThreadFCT(TLD);
+  }
 
   // Then we force serialize the log data.
   profileCollectorService::serialize();
@@ -284,7 +289,13 @@ profilingLoggingInit(UNUSED size_t Buffe
       if (TLD.Allocators == nullptr && TLD.FCT == nullptr)
         return;
 
-      postCurrentThreadFCT(TLD);
+      {
+        // If we're somehow executing this while inside a non-reentrant-friendly
+        // context, we skip attempting to post the current thread's data.
+        RecursionGuard G(ReentranceGuard);
+        if (G)
+          postCurrentThreadFCT(TLD);
+      }
     });
 
     // We also need to set up an exit handler, so that we can get the profile