Hi, note your printf line is missing. if you printf l_prev, then the valgrind error occurs in all variants
at first glance, it looks like a false positive, and i will investigate it Cheers, Gilles On Sat, Nov 5, 2016 at 7:59 PM, Yvan Fournier <yvan.fourn...@free.fr> wrote: > Hello, > > I have observed what seems to be false positives running under Valgrind when > Open MPI is build with --enable-memchecker > (at least with versions 1.10.4 and 2.0.1). > > Attached is a simple test case (extracted from larger code) that sends one > int to rank r+1, and receives from rank r-1 > (using MPI_COMM_NULL to handle ranks below 0 or above comm size). > > Using: > > ~/opt/openmpi-2.0/bin/mpicc -DVARIANT_1 vg_mpi.c > ~/opt/openmpi-2.0/bin/mpiexec -output-filename vg_log -n 2 valgrind ./a.out > > I get the following Valgrind error for rank 1: > > ==8382== Invalid read of size 4 > ==8382== at 0x400A00: main (in /home/yvan/test/a.out) > ==8382== Address 0xffefffe70 is on thread 1's stack > ==8382== in frame #0, created by main (???:) > > > Using: > > ~/opt/openmpi-2.0/bin/mpicc -DVARIANT_2 vg_mpi.c > ~/opt/openmpi-2.0/bin/mpiexec -output-filename vg_log -n 2 valgrind ./a.out > > I get the following Valgrind error for rank 1: > > ==8322== Invalid read of size 4 > ==8322== at 0x400A6C: main (in /home/yvan/test/a.out) > ==8322== Address 0xcb6f9a0 is 0 bytes inside a block of size 4 alloc'd > ==8322== at 0x4C29BBE: malloc (in > /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) > ==8322== by 0x400998: main (in /home/yvan/test/a.out) > > I get no error for the default variant (no -D_VARIANT...) with either Open > MPI 2.0.1, or 1.10.4, > but de get an error similar to variant 1 on the parent code from which the > example was extracted... > > is given below. Running under Valgrind's gdb server, for the parent code of > variant 1, > it even seems the value received on rank 1 is uninitialized, then Valgrind > complains > with the given message. > > The code fails to work as intended when run under Valgrind when OpenMPI is > built with --enable-memchecker, > while it works fine when run with the same build but not under Valgrind, > or when run under Valgrind with Open MPI built without memchecker. > > I'm running under Arch Linux (whosed packaged Open MPI 1.10.4 is built with > memchecker enabled, > rendering it unusable under Valgrind). > > Did anybody else encounter this type of issue, or I does my code contain an > obvious mistake that I am missing ? > I initially though of possible alignment issues, but saw nothing in the > standard that requires that, > and the "malloc"-base variant exhibits the same behavior,while I assume > alignment to 64-bits for allocated arrays is the default. > > Best regards, > > Yvan Fournier > _______________________________________________ > users mailing list > users@lists.open-mpi.org > https://rfd.newmexicoconsortium.org/mailman/listinfo/users _______________________________________________ users mailing list users@lists.open-mpi.org https://rfd.newmexicoconsortium.org/mailman/listinfo/users
