[petsc-dev] Infinite loop in A*B

[Zhang, Hong]

Pierre,
I pushed a fix in branch hzhang/fix-matmatmult_aij_dense/release. https://gitlab.com/petsc/petsc/-/merge_requests/3667
[https://assets.gitlab-static.net/uploads/-/system/project/avatar/13882401/PETSc_RBG-logo.png]<https://gitlab.com/petsc/petsc/-/merge_requests/3667>
bugfix for MatMatMultSymbolic_MPIAIJ_MPIDense() when Bbn1 = 0. (!3667) · Merge Requests · PETSc / petsc<https://gitlab.com/petsc/petsc/-/merge_requests/3667>
Reported-by: Pierre Jolivet pierre at joliv.et Bb (column block size) cannot be zero; it leads to infinite loop in MatMatMultNumeric_MPIAIJ_MPIDense() with n=0
gitlab.com
Give it a try. Let me know if the bug is not fixed.
Your code is very helpful in debugging.
Hong

________________________________
From: Pierre Jolivet <pierre at joliv.et>
Sent: Monday, March 1, 2021 12:51 AM
To: Zhang, Hong <hzhang at mcs.anl.gov>
Cc: For users of the development version of PETSc <petsc-dev at mcs.anl.gov>
Subject: Re: [petsc-dev] Infinite loop in A*B


On 1 Mar 2021, at 6:29 AM, Zhang, Hong <hzhang at mcs.anl.gov<mailto:hzhang at mcs.anl.gov>> wrote:

Pierre,
This is a bug in MatMatMultSymbolic_MPIAIJ_MPIDense() during optimization of block column size of B. Run your code with
'-matmatmult_Bbn 1', the infinite loop should not occur.

Thanks Hong, I can confirm this option makes the more complex use case run smoothly as well.

I'll try to figure out a fix tomorrow.

Great.

Thanks,
Pierre

Hong
________________________________
From: Zhang, Hong <hzhang at mcs.anl.gov<mailto:hzhang at mcs.anl.gov>>
Sent: Sunday, February 28, 2021 11:05 PM
To: Pierre Jolivet <pierre at joliv.et<mailto:pierre at joliv.et>>; For users of the development version of PETSc <petsc-dev at mcs.anl.gov<mailto:petsc-dev at mcs.anl.gov>>; Zhang, Hong <hzhang at mcs.anl.gov<mailto:hzhang at mcs.anl.gov>>
Subject: Re: [petsc-dev] Infinite loop in A*B

The infinite loop in MatMatMultNumeric_MPIAIJ_MPIDense()
for (i=0; i<BN; i+=n) {
}
is cause by n=contents->workB->cmap->n=0 (line 590 in mpimatmatmult.c)
Hong
________________________________
From: petsc-dev <petsc-dev-bounces at mcs.anl.gov<mailto:petsc-dev-bounces at mcs.anl.gov>> on behalf of Zhang, Hong via petsc-dev <petsc-dev at mcs.anl.gov<mailto:petsc-dev at mcs.anl.gov>>
Sent: Sunday, February 28, 2021 10:33 PM
To: Pierre Jolivet <pierre at joliv.et<mailto:pierre at joliv.et>>; For users of the development version of PETSc <petsc-dev at mcs.anl.gov<mailto:petsc-dev at mcs.anl.gov>>
Subject: Re: [petsc-dev] Infinite loop in A*B

I can reproduce the hang with
mpiexec -n 2 ./matmatmult

It seems in an infinite loop of calling MatDensePlaceArray() from

#0  MatDensePlaceArray (mat=0xda5c50, array=0xd15e60)
    at /home/hongsu/soft/petsc/src/mat/impls/dense/mpi/mpidense.c:2047
#1  0x00007fa0d13bf4f7 in MatDenseGetSubMatrix_SeqDense (A=0xcfb2b0, cbegin=0,
    cend=0, v=0xd90370)
    at /home/hongsu/soft/petsc/src/mat/impls/dense/seq/dense.c:2997
#2  0x00007fa0d13c574e in MatDenseGetSubMatrix (A=0xcfb2b0, cbegin=0, cend=0,
    v=0xd90370) at /home/hongsu/soft/petsc/src/mat/impls/dense/seq/dense.c:3371
#3  0x00007fa0d13db5ce in MatDenseGetSubMatrix_MPIDense (A=0xca5250, cbegin=0,
    cend=0, v=0x7ffe87d41de0)
    at /home/hongsu/soft/petsc/src/mat/impls/dense/mpi/mpidense.c:1835
#4  0x00007fa0d13c574e in MatDenseGetSubMatrix (A=0xca5250, cbegin=0, cend=0,
    v=0x7ffe87d41de0)
    at /home/hongsu/soft/petsc/src/mat/impls/dense/seq/dense.c:3371
#5  0x00007fa0d179c2fa in MatMatMultNumeric_MPIAIJ_MPIDense (A=0xc55490,
    B=0xca5250, C=0xd282b0)
    at /home/hongsu/soft/petsc/src/mat/impls/aij/mpi/mpimatmatmult.c:593
#6  0x00007fa0d1181331 in MatProductNumeric_AB (mat=0xd282b0)
    at /home/hongsu/soft/petsc/src/mat/interface/matproduct.c:567
#7  0x00007fa0d1182c14 in MatProductNumeric (mat=0xd282b0)
    at /home/hongsu/soft/petsc/src/mat/interface/matproduct.c:679
#8  0x00007fa0d115ef69 in MatProduct_Private (A=0xc55490, B=0xca5250,
    scall=MAT_INITIAL_MATRIX, fill=-2, ptype=MATPRODUCT_AB, C=0x7ffe87d42018)
    at /home/hongsu/soft/petsc/src/mat/interface/matrix.c:9405
---Type <return> to continue, or q <return> to quit---
#9  0x00007fa0d115f274 in MatMatMult (A=0xc55490, B=0xca5250, scall=MAT_INITIAL_MATRIX, fill=-2,
    C=0x7ffe87d42018) at /home/hongsu/soft/petsc/src/mat/interface/matrix.c:9445
#10 0x000000000040130a in main (argc=2, argv=0x7ffe87d42108) at ex1.c:20

I'll try to figure out what is going on. If anyone has a clue, please help. The above stack comes from 'release' branch.
Hong
________________________________
From: petsc-dev <petsc-dev-bounces at mcs.anl.gov<mailto:petsc-dev-bounces at mcs.anl.gov>> on behalf of Pierre Jolivet <pierre at joliv.et<mailto:pierre at joliv.et>>
Sent: Sunday, February 28, 2021 4:17 PM
To: For users of the development version of PETSc <petsc-dev at mcs.anl.gov<mailto:petsc-dev at mcs.anl.gov>>
Subject: [petsc-dev] Infinite loop in A*B

Hello,
The following MWE loops indefinitely for MPI_Comm_size in {2; 3}.
Nothing fancy, just MatAIJ and MatDense.
The problem is either in MatMPIDenseScatter() or MatMatMultSymbolic_MPIAIJ_MPIDense(), I believe, so if someone familiar with those routines can figure out a hot fix, I’m all ears.
I could of course switch to a MatMult(), but the same infinite loop happens in another more complex code with
A = rows=8, cols=35212
B = rows=35212, cols=9
So I’ll need a fix eventually.

Thanks,
Pierre

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