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We are developing a static race detection tool and we found a few potential data races in this project. We were unable to determine if these races are possible under some input, so we thought it best to report just in case.

Potential Race on temp

We found a potential race on temp inside of the parallel loop at seq_mv/csr_matvec.c:747.

#ifdef HYPRE_USING_OPENMP
#pragma omp parallel for private(i,jj) HYPRE_SMP_SCHEDULE
#endif

   for (i = 0; i < num_rows; i++)
   {
      if (CF_marker_x[i] == fpt)
      {
         temp = y_data[i];
         for (jj = A_i[i]; jj < A_i[i+1]; jj++)
            if (CF_marker_y[A_j[jj]] == fpt) temp += A_data[jj] * x_data[A_j[jj]];
         y_data[i] = temp;
      }
   }

There are two writes to tmp

• temp = y_data[i];
• temp += A_data[jj] ...

We were unable to confirm if the branch conditions guarding these writes prevent multiple threads from executing these writes in parallel.

Was temp intended to be marked private?

I have pasted the full report from our tool below for reference.

==== Found a race between: 
line 754, column 10 in csr_matvec.c AND line 756, column 51 in csr_matvec.c
Shared variable: 
temp at line 675 of csr_matvec.c
 675|   HYPRE_Complex      temp;
Thread 1: 
 752|      if (CF_marker_x[i] == fpt)
 753|      {
>754|         temp = y_data[i];
 755|         for (jj = A_i[i]; jj < A_i[i+1]; jj++)
 756|            if (CF_marker_y[A_j[jj]] == fpt) temp += A_data[jj] * x_data[A_j[jj]];
>>>Stack Trace:
>>>.omp_outlined._debug__.36.414 [csr_matvec.c:750]
Thread 2: 
 754|         temp = y_data[i];
 755|         for (jj = A_i[i]; jj < A_i[i+1]; jj++)
>756|            if (CF_marker_y[A_j[jj]] == fpt) temp += A_data[jj] * x_data[A_j[jj]];
 757|         y_data[i] = temp;
 758|      }
>>>Stack Trace:
>>>.omp_outlined._debug__.36.414 [csr_matvec.c:750]
The OpenMP region this bug occurs:
/home/brad/tmp/AMG/seq_mv/csr_matvec.c
>747|#pragma omp parallel for private(i,jj) HYPRE_SMP_SCHEDULE
 748|#endif
 749|
 750|   for (i = 0; i < num_rows; i++)
 751|   {
 752|      if (CF_marker_x[i] == fpt)

Potential Race on res0

The second potential race we identified occurs on res0 inside of the parallel loop at parcsr_ls/par_relax.c:1444.
There are writes to res0 at lines 1470 and 1477:

• res0 = 0.0;
• res0 -= A_diag_data[jj] ...

#ifdef HYPRE_USING_OPENMP
#pragma omp parallel for private(i,ii,j,jj,ns,ne,res,rest,size) HYPRE_SMP_SCHEDULE
#endif
for (j = 0; j < num_threads; j++)
{
    ....
    for (i = ne-1; i > ns-1; i--)	/* interior points first */
    {

        /*-----------------------------------------------------------
        * If diagonal is nonzero, relax point i; otherwise, skip it.
        *-----------------------------------------------------------*/
        
        if ( A_diag_data[A_diag_i[i]] != zero)
        {
            res = f_data[i];
            res0 = 0.0; // <================================= Racing Write
            res2 = 0.0;
            for (jj = A_diag_i[i]+1; jj < A_diag_i[i+1]; jj++)
            {
                ii = A_diag_j[jj];
                if (ii >= ns && ii < ne)
                {
                    res0 -= A_diag_data[jj] * u_data[ii]; // <=== Racing Write

We were unable to determine if the branches guarding these writes would prevent multiple threads from accessing these lines.

If this is a real race, there is a nearly identical case in the parallel loop at parcsr_ls/ams.c:3783 on the variable res2.

I ran AMG on Xeon, KNL and KNM platform, but when I was running on KNM/KNL I find that the numbers of iterations become much more than on Xeon(with same configuration), what's more, when I running with 1 OMP thread per process, the number of iterations will become 0 on KNM/KNL, is there any way(like some flag) to control the number of iteration, or this is a problem of the code?

Perhaps this is a strange question, and I am not sure if the project author is still actively involved in it, but I thought I would give it a try and inquire. Here's the situation: Firstly, I have successfully built the project using the make command. However, when I attempted to compile and run amg.c separately using different approaches (I am using the Clang compiler), I encountered the following issues:

1. amg.c can be successfully compiled into an executable file directly using Clang, and it can run smoothly. The command is as follows:
   clang -fopenmp -o test4 amg.c -I.. -I../utilities -I../IJ_mv -I../seq_mv -I../parcsr_mv -I../parcsr_ls -I../krylov -DTIMER_USE_MPI -DHYPRE_USING_OPENMP -DHYPRE_HOPSCOTCH -DHYPRE_USING_PERSISTENT_COMM -DHYPRE_BIGINT -DHYPRE_TIMING -lmpi -L. -L../parcsr_ls -L../parcsr_mv -L../IJ_mv -L../seq_mv -L../krylov -L../utilities -lparcsr_ls -lparcsr_mv -lseq_mv -lIJ_mv -lkrylov -lHYPRE_utilities -lm
2. However, when I followed the steps below to convert amg.c into an executable file, I encountered different errors during the execution:
   ①
   clang -S -emit-llvm -o amgtest.ll amgtest.c
clang amgtest.ll -fopenmp -DTIMER_USE_MPI -DHYPRE_USING_OPENMP -DHYPRE_HOPSCOTCH -DHYPRE_USING_PERSISTENT_COMM -DHYPRE_BIGINT -DHYPRE_TIMING -lmpi -L. -L../parcsr_ls -L../parcsr_mv -L../IJ_mv -L../seq_mv -L../krylov -L../utilities -lparcsr_ls -lparcsr_mv -lseq_mv -lIJ_mv -lkrylov -lHYPRE_utilities -lm -o test4 -g
mpirun -np 4 test4
   Output:
   
   ②
   clang -S -emit-llvm -o amgtest.ll amgtest.c
llvm-as amgtest.ll -o amgtest.bc
llc amgtest.bc -o amgtest.s
clang amgtest.s -no-pie -fopenmp -DTIMER_USE_MPI -DHYPRE_USING_OPENMP -DHYPRE_HOPSCOTCH -DHYPRE_USING_PERSISTENT_COMM -DHYPRE_BIGINT -DHYPRE_TIMING -lmpi -L. -L../parcsr_ls -L../parcsr_mv -L../IJ_mv -L../seq_mv -L../krylov -L../utilities -lparcsr_ls -lparcsr_mv -lseq_mv -lIJ_mv -lkrylov -lHYPRE_utilities -lm -o test4 -g
mpirun -np 4 test4
   Output:
   
   I identified the function where the error occurred through GDB debugging. After adding some debugging information, I found that the issue was related to the IJ_A structure.
   
   I suspect that the error occurred during the conversion of the amg.c code into intermediate code due to the complexity of the IJ_A structure. This may have resulted in some unexpected errors, leading to the final error. I have ruled out the issue of compiler versions (as I have tried Clang 3.8, Clang 4.0, and Clang 3.0). Could it be a problem with the code itself? Have the authors encountered similar errors before? (Since my current research is in code optimization/profiling, I need to manipulate the intermediate code of amg.c). Do you have any suggestions? Thank you very much!

I just wanted to give huge props and say thank you for how easy this was to build, and find examples for running here! I literally typed make in an environment with the dependencies (all installed easily with apt) and it worked, and then the example problems did too.

Please close this after reading, just wanted to say thank you! 🙌