bug in tfs preconditioner

[Stephan Kramer]

Hi all,

I think I found a nasty bug in the tfs preconditioner/solver. The first symptons were MPI complaints about corrupted messages in MPI_WAIT on line 1552 of ksp/pc/impls/tfs/gs.c (the file is the same in 
petsc-dev and 3.0.0). Valgrind suggested a buffer overrun (in reading) in MPI_Isend of line 1533:


   ierr = MPI_Isend(dptr3, *msg_size++, MPIU_SCALAR, *list++, MSGTAG1+my_id, gs->gs_comm, msg_ids_out++);CHKERRQ(ierr);

Stepping through with a debugger however it looked like everything going into the MPI_Isends and MPI_Irecvs was perfectly fine. Until I realised that they were both replaced by a macro from petsclog.h:

#define MPI_Isend(buf,count,datatype,dest,tag,comm,request) \
  ((isend_ct++,0) || TypeSize(&isend_len,count,datatype) || MPI_Isend(buf,count,datatype,dest,tag,comm,request))

Because count is used twice in that expression, the argument *msg_size++ is evaluated twice, and only gives the right integer value in calling TypeSize, and will be wrong in the actual MPI_Isend call. 
   The same thing is going on on line 1327 of gs.c btw. If someone has time to look into this, it would be much appreciated. Has the tfs solver been used/applied much, as far as people know?

Cheers
Stephan

-- 
Stephan Kramer  <s.kramer at imperial.ac.uk>
Applied Modelling and Computation Group,
Department of Earth Science and Engineering,
Imperial College London