Function copy_to_user() returns number of bytes that could not be copied, and a non-zero return value often means errors. In function lstcon_group_info() defined in file drivers/staging/lustre/lnet/selftest/console.c, however, 0 (indicates success) may be returned even when copy_to_user() returns a non-zero value. Maybe the author intends to return "rc" instead of "0" at line 823. Codes related to this bug are summarised as follows.

lstcon_group_info @@ drivers/staging/lustre/lnet/selftest/console.c
 779 int
 780 lstcon_group_info(char *name, lstcon_ndlist_ent_t __user *gents_p,
 781           int *index_p, int *count_p,
 782           lstcon_node_ent_t __user *dents_up)
 783 {
 784     lstcon_ndlist_ent_t *gentp;
 785     struct lstcon_group *grp;
 786     struct lstcon_ndlink *ndl;
 787     int rc;
 788 
 789     rc = lstcon_group_find(name, &grp);
 790     if (rc) {
 791         CDEBUG(D_NET, "Can't find group %s\n", name);
 792         return rc;
 793     }

         ...
 816     rc = copy_to_user(gents_p, gentp,
 817               sizeof(lstcon_ndlist_ent_t)) ? -EFAULT : 0;
 818 
 819     LIBCFS_FREE(gentp, sizeof(lstcon_ndlist_ent_t));
 820 
 821     lstcon_group_decref(grp);
 822  
 823     return 0;      // return rc?
 824 }

Thanks very much!