mv_cesa dcache problem since 2.6.37 was: Re: mv_cesa hash functions

[Simon Baatz <gmbnomis@gmail.com>]

Hi,

Am 23.02.2012 19:34, schrieb Phil Sutter:
> But you might suffer from another problem, which is only present on
> ARM machines with VIVT cache and linux >= 2.6.37: due to commit
> f8b63c1, "ARM: 6382/1: Remove superfluous flush_kernel_dcache_page()"
> which prevents pages being flushed from inside the scatterlist
> iterator API. This patch seems to introduce problems in other places
> (namely NFS), too but I sadly did not have time to investigate this
> further. I will post a possible (cryptodev-internal) solution to
> cryptodev-linux-devel@gna.org, maybe this fixes the problem with
> openssl. Greetings, Phil 

since there has been no reaction on this, I would like to bring this
issue up again (I sadly don't have the expertise to investigate this
further...). The issue is not limited to cryptodev, but seems to be
either a problem with commit f8b63c1 or a problem in mv_cesa that was
uncovered by this commit. In the past, I also had massive problems
compiling on an NFS mounted file system when not reverting f8b63c1. I
currently can't reproduce this anymore under 3.4-rc5.

However, the following still happens on a 3.4-rc5 preempt kernel on arm
kirkwood (VIVT cache):

root@ww1:~# cryptsetup luksOpen /dev/sda2 c_sda2
Enter passphrase for /dev/sda2:
root@ww1:~# vgchange -a y ww1_1
  Volume group "ww1_1" not found
root@ww1:~# vgchange -a y ww1_1
Segmentation fault


Thus, the behavior of vgchange is unpredictable on a dm-crypt device
when using mv_cesa (btw. the machine needs to have no load to show this
behavior. I assume that the cache flushes caused by task switches make
it work under load).

Using the generic crypto modules, it works as expected:

root@ww1:~# cryptsetup luksClose c_sda2
root@ww1:~# rmmod mv_cesa
root@ww1:~# cryptsetup luksOpen /dev/sda2 c_sda2
Enter passphrase for /dev/sda2:
root@ww1:~# vgchange -a y ww1_1
  1 logical volume(s) in volume group "ww1_1" now active


After reverting f8b63c1, it works as expected using mv_cesa as well.


- Simon