Sorry, I pushed the wrong button and sent this before it was ready....
Tim Prins wrote:
Hi folks,
I am running into a problem with the ibm test 'group'. I will try to
explain what I think is going on, but I do not really understand the
group code so please forgive me if it is wrong...
The test creates a group based on MPI_COMM_WORLD (group1), and a group
that has half the procs in group1 (newgroup). Next, all the processes do:
MPI_Group_intersection(newgroup,group1,&group2)
ompi_group_intersection figures out what procs are needed for group2,
then calls
ompi_group_incl, passing 'newgroup' and '&group2'
This then calls (since I am not using sparse groups) ompi_group_incl_plist
However, ompi_group_plist assumes that the current process is a member
of the passed group ('newgroup'). Thus when it calls
ompi_group_peer_lookup on 'newgroup', half of the processes get garbage
back since they are not in 'newgroup'. In most cases, memory is
initialized to \0 and things fall through, but we get intermittent
segfaults in optimized builds.
Here is a patch to a error check which highlights the problem:
Index: group/group.h
===================================================================
--- group/group.h (revision 15869)
+++ group/group.h (working copy)
@@ -308,7 +308,7 @@
static inline struct ompi_proc_t* ompi_group_peer_lookup(ompi_group_t
*group, int peer_id)
{
#if OMPI_ENABLE_DEBUG
- if (peer_id >= group->grp_proc_count) {
+ if (peer_id >= group->grp_proc_count || peer_id < 0) {
opal_output(0, "ompi_group_lookup_peer: invalid peer index
(%d)", peer_id);
Thanks,
Tim
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