Apologies if you will get this message twice. My ISP seems to be
blocked in hub.freebsd.org so I had to use temporary hotmail account.

    I found the reason for crashes I was experiencing ever since UMA has
been committed into -CURRENT.  Apparently UMA has nothing to do with the
breakage. The real problem lies in vfs_opv_recalc function from
vfs_ini.c.  Then kernel loads dynamic filesystem module, it looks for
any of the VOP operations specified by the new filesystem that have not
been registered already by the currently known filesystems. If any of
such operations exist, vfs_add_vnops function calls vfs_opv_recalc
function, which rebuilds vop_t vectors for each filesystem and sets all
global pointers like ufs_vnops_p, devfs_specop_p, etc to the new values
and then frees the old pointers.  This behavior is bad because there
might be already active vnodes whose v_op fields will be left pointing
to the random garbage, leading to inevitable crash soon.
  I used the workaround below to get the system booting again, but it
does nothing to solve the real problem. We should probably either update
each and every vnode known to the system with the new v_op pointer when
needed, or simply start allocating vop_t vectors large enough to hold
every vnode operation we know about. Or maybe some VFS guru can
propose a better strategy?

Index: vfs_init.c
RCS file: /home/ncvs/src/sys/kern/vfs_init.c,v
retrieving revision 1.57
diff -u -r1.57 vfs_init.c
--- vfs_init.c  20 Mar 2002 04:09:58 -0000      1.57
+++ vfs_init.c  23 Mar 2002 04:22:00 -0000
@@ -129,8 +129,10 @@
        for (i = 0; i < vnodeopv_num; i++) {
                opv = vnodeopv_descs[i];
                opv_desc_vector_p = opv->opv_desc_vector_p;
+#if 0
                if (*opv_desc_vector_p)
                        FREE(*opv_desc_vector_p, M_VNODE);
                MALLOC(*opv_desc_vector_p, vop_t **,
                        vfs_opv_numops * sizeof(vop_t *), M_VNODE,
                        M_WAITOK | M_ZERO);

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