Apply by doing:
       cd /usr/src
       patch -p0 < 015_sysvshm.patch

And then rebuild your kernel.

Index: sys/kern/sysv_shm.c
===================================================================
RCS file: /cvs/src/sys/kern/sysv_shm.c,v
retrieving revision 1.33
diff -u -r1.33 sysv_shm.c
--- sys/kern/sysv_shm.c 7 Jan 2003 00:34:41 -0000       1.33
+++ sys/kern/sysv_shm.c 5 Feb 2004 21:36:31 -0000
@@ -281,8 +281,10 @@
       error = uvm_map(&p->p_vmspace->vm_map, &attach_va, size,
           shm_handle->shm_object, 0, 0, UVM_MAPFLAG(prot, prot,
           UVM_INH_SHARE, UVM_ADV_RANDOM, 0));
-       if (error)
+       if (error) {
+               uao_detach(shm_handle->shm_object);
               return (error);
+       }

       shmmap_s->va = attach_va;
       shmmap_s->shmid = SCARG(uap, shmid);