[Openmp-commits] [openmp] d83ca62 - [OpenMP] Fix data-race in new device RTL

[Joseph Huber via Openmp-commits]

Author: Joseph Huber
Date: 2021-09-23T17:28:07-04:00
New Revision: d83ca624a1d52b600ddbd8bfcbb3d5d7c6003af7

URL: https://github.com/llvm/llvm-project/commit/d83ca624a1d52b600ddbd8bfcbb3d5d7c6003af7
DIFF: https://github.com/llvm/llvm-project/commit/d83ca624a1d52b600ddbd8bfcbb3d5d7c6003af7.diff

LOG: [OpenMP] Fix data-race in new device RTL

This patch fixes a data-race observed when using the new device runtime
library. The Internal control variable for the parallel level is read in
the `__kmpc_parallel_51` function while it could potentially be written
by other threads. This causes data corruption and will cause
nondetermistic behaviour in the runtime. This patch fixes this by adding
an explicit synchronization before the region starts.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D110366

Added: 
    

Modified: 
    openmp/libomptarget/DeviceRTL/src/Parallelism.cpp

Removed: 
    


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diff  --git a/openmp/libomptarget/DeviceRTL/src/Parallelism.cpp b/openmp/libomptarget/DeviceRTL/src/Parallelism.cpp
index 367c2966f10e9..afb0704f2642e 100644
--- a/openmp/libomptarget/DeviceRTL/src/Parallelism.cpp
+++ b/openmp/libomptarget/DeviceRTL/src/Parallelism.cpp
@@ -93,6 +93,7 @@ void __kmpc_parallel_51(IdentTy *ident, int32_t, int32_t if_expr,
 
   uint32_t NumThreads = determineNumberOfThreads(num_threads);
   if (mapping::isSPMDMode()) {
+    synchronize::threads();
     {
       state::ValueRAII ParallelTeamSizeRAII(state::ParallelTeamSize, NumThreads,
                                             1u, TId == 0);