Bug 480136

The crash utility needs to take the "name" of the module as
seen by "lsmod", and then search the local /lib/modules/<release>
directory tree for the associated module.

Sometimes modules are named with strings containing underscores ('_'),
whereas their associated object file uses dashes ('-').

So in kernel version 2.6.18-92.el5, "lsmod" and the crash utility
"mod" command will show dm_crypt, dm_emc, dm_hp_sw, dm_mirror, dm_mod,
dm_multipath, dm_rdac, dm_round_robin, dm_stapshot, and dm_zero.
When searching the local filesystem, the crash utility will first
look for a module with the same name, and if can't find it, it will
try again substituting "_" for "-", and so it finds them here:  

  $ rpm -qpl kernel-2.6.18-92.el5.x86_64.rpm | grep dm-
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-crypt.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-emc.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-hp-sw.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-mirror.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-mod.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-multipath.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-rdac.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-round-robin.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-snapshot.ko
  /lib/modules/2.6.18-92.el5/kernel/drivers/md/dm-zero.ko
  $

So when crash looks for the module object file for "dm_crypt",
it first searches for "dm_crypt.ko", and when it fails, it then
tries for "dm-crypt.ko" and finds it OK.

This later set of modules does not follow convention, specifically
the "dm_region_hash" module.  The crash utility first looks for 
"dm_region_hash.ko", and doesn't find it; so then it replaces the
underscores with dashes, and looks for "dm-region-hash.ko" module.
But it doesn't find that either:

  mod: cannot find or load object file for dm_region_hash module

And that's because the driver writer did not follow convention
for that particular module:

  $ rpm -qpl kernel-2.6.18-128.el5.x86_64.rpm | grep dm-
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-crypt.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-emc.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-hp-sw.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-log.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-mem-cache.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-message.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-mirror.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-mod.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-multipath.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-raid45.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-rdac.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-region_hash.ko  <<<<<<
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-round-robin.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-snapshot.ko
  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-zero.ko
  $

Note the module name uses both underscores and dashes, i.e.,
"dm-region_hash.ko". 

So the crash utility cannot find it automatically using its current
search algorithm.

It's certainly easy enough to work around:

  crash> mod -s dm_region_hash /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-region_hash.ko
       MODULE       NAME               SIZE  OBJECT FILE
  ffffffff88152200  dm_region_hash    46145  /lib/modules/2.6.18-128.el5/kernel/drivers/md/dm-region_hash.ko 
  crash> 

But I note that the current set of 128.el5 modules for x86_64
has these modules containing both '_' and '-' characters:

  aes-x86_64.ko
  dm-region_hash.ko
  nls_euc-jp.ko
  nls_iso8859-1.ko
  nls_iso8859-13.ko
  nls_iso8859-14.ko
  nls_iso8859-15.ko
  nls_iso8859-2.ko
  nls_iso8859-3.ko
  nls_iso8859-4.ko
  nls_iso8859-5.ko
  nls_iso8859-6.ko
  nls_iso8859-7.ko
  nls_iso8859-9.ko
  nls_koi8-r.ko
  nls_koi8-ru.ko
  nls_koi8-u.ko

And so for example, if I insmod aes-x86_64.ko, the module is named
"aes_x86_64":

  $ insmod /lib/modules/2.6.18-92.el5/kernel/arch/x86_64/crypto/aes-x86_64.ko
  $ lsmod
  Module                  Size  Used by
  aes_x86_64             58601  0 
  ...

And not surprisingly, if try to load it on the live system with crash:

  crash> mod -S
  ...
  mod: cannot find or load object file for aes_x86_64 module
  ...

So let me revisit the crash utility's search scheme.

Good catch!

Thanks,
  Dave

Release note added. If any revisions are required, please set the 
"requires_release_notes" flag to "?" and edit the "Release Notes" field accordingly.
All revisions will be proofread by the Engineering Content Services team.

New Contents:
The "mod -[sS]" command would fail with the error message: "mod: cannot find or load object file for <name> module" if the target module object filename contains both underscore and dash characters. Crash now parses these filenames correctly.

Release note looks fine.

An advisory has been issued which should help the problem
described in this bug report. This report is therefore being
closed with a resolution of ERRATA. For more information
on therefore solution and/or where to find the updated files,
please follow the link below. You may reopen this bug report
if the solution does not work for you.

http://rhn.redhat.com/errata/RHBA-2009-1283.html