RE: md as module cannot be reloaded.

-----Original Message-----
From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
owner@vger.kernel.org] On Behalf Of Hawrylewicz Czarnowski, Przemyslaw
Sent: Thursday, December 02, 2010 12:42 AM
To: Neil Brown
Cc: linux-raid@vger.kernel.org; Labun, Marcin; Czarnowska, Anna; Neubauer,
Wojciech; Williams, Dan J; Ciechanowski, Ed
Subject: RE: md as module cannot be reloaded.

quoted

-----Original Message-----
From: linux-raid-owner@vger.kernel.org [mailto:linux-raid-
owner@vger.kernel.org] On Behalf Of Neil Brown
Sent: Wednesday, December 01, 2010 10:57 PM
To: Hawrylewicz Czarnowski, Przemyslaw
Cc: linux-raid@vger.kernel.org; Labun, Marcin; Czarnowska, Anna;

Neubauer,

quoted

Wojciech; Williams, Dan J; Ciechanowski, Ed
Subject: Re: md as module cannot be reloaded.

On Wed, 1 Dec 2010 14:23:14 +0000 "Hawrylewicz Czarnowski, Przemyslaw"
[off-list ref] wrote:

quoted

Hi,

I have found an annoying problem with md module. If it is compiled as

loadable module it is impossible to reload module if unloaded once.

quoted

Eg.
# mdadm -Ss
# modprobe -r raid1 && modprobe -r md-mod
# cat /proc/modules | grep md_mod || echo Unloaded
Unloaded
# cat /proc/mdstat
cat /proc/mdstat: Invalid arguments

I cannot reproduce this.  That this point I get

cat: /proc/mdstat: No such file or directory

quoted

# modprobe md-mod
# cat /proc/mdstat
cat /proc/mdstat: Invalid argument
# cat /proc/modules | grep md_mod || echo Unloaded
md_mod 94178 0 - Live 0xf857a000

Some functionalities seem to work, but nothing is able to read

/proc/mdstat.

quoted

If have tried few kernels from 2.6.27 to 2.6.37-rc3, openSUSE

11.x/RHEL6,

quoted

doesn't matter, still the same result. What can be wrong?

openSUSE doesn't compile md as a module, it is compiled in to the kernel.
But presumably you are compiling your own kernel with md as a module?  Is
that right?  You aren't compiling a module and loading it into a kernel
which
already has md in it are you?  I don't think that would work anyway...

Yes, I have recompiled kernel with MD as module.

quoted

And you give a full sequence of commands from loading to unload that
reliably
produces this error for you?

Ok, here you are:
* Original opensuse config updated to new kernel with defaults
* Changed CONFIG_BLK_DEV_MD=y->m
* Added prefix -mdadm

make
su
make modules_install
make install
mdadm -Ss
mdadm --zero-superblock /dev/sd[b-g]
reboot
...
localhost:~ # uname -r
2.6.37-rc3-pae-mdadm
localhost:~ # cat /proc/mdstat
cat: /proc/mdstat: No such file or directory
localhost:~ # cat /proc/modules | grep md_mod
localhost:~ # modprobe md_mod
localhost:~ # ll /proc/mdstat
-r--r--r-- 1 root root 0 Dec  2 00:14 /proc/mdstat
localhost:~ # cat /proc/mdstat
Personalities :
unused devices: <none>
localhost:~ # modprobe -r md_mod
localhost:~ # ll /proc/mdstat
-r--r--r-- 1 root root 0 Dec  2 00:14 /proc/mdstat
localhost:~ # cat /proc/mdstat
cat: /proc/mdstat: Invalid argument
localhost:~ # modprobe -r md_mod

Here is just "modprobe md_mod" of course...

localhost:~ # ll /proc/mdstat
-r--r--r-- 1 root root 0 Dec  2 00:14 /proc/mdstat
localhost:~ # cat /proc/mdstat
cat: /proc/mdstat: Invalid argument

that's all.

And another scenario - it might put some new light at this problem:

[system right after restart]

localhost:~ # mdadm -Ss
mdadm: stopped /dev/md126
mdadm: stopped /dev/md127
localhost:~ # cat /proc/mdstat
Personalities : [raid1]
unused devices: <none>
localhost:~ # modprobe -r raid1
localhost:~ # ll /proc/mdstat
-r--r--r-- 1 root root 0 Dec  9 16:52 /proc/mdstat
localhost:~ # cat /proc/mdstat
cat: /proc/mdstat: Invalid argument

One more thing... For some time everything worked perfectly. And problem appeared again after few days.
I do not remember any unusual activity which may change this behavior.

quoted

NeilBrown

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