Subject: (fwd) linux SEGV details

From: [email-masked] (Ariel Faigon)
Date: Wed, 17 Jun 1998 08:43:11 -0700 (PDT)

[forwarding bounced message from non subscriber]

----- Forwarded message from owner-linux@cthulhu -----
To: [email-masked] (Honza Pazdziora)
Date: Wed, 17 Jun 1998 09:18:17 +0200 (MET DST)
Cc: [email-masked], [email-masked],
        [email-masked]
X-Mailer: ELM [version 2.4ME+ PL39 (25)]

Honza Pazdziora wrote:
> > Do you mean that mkswap segfaulted during install, or after?  I'll have a
> > closer look.  The util-linux we're using is a little old.

It segfault during install _and_ after install when we tried to set up
swap space manualy.

> 
> I'm not sure what happened during install -- I just wanted to have it
> done to see the real prompt ;-) But when I tried mkswap /dev/sdb2 on
> the prompt, it said something about freeing free buffer? (or whatever)
> and then gave register dump. Sorry, I'm at home and can't get to the
> machine because sshd isn't running there yet, so I will send the exact
> output tomorrow.

Honza is not yet here, so there is the output:

#mkswap /dev/sdb2
Segmentation fault
#

and on console (there is no syslogd :( ) is:

#dmesg
[...skipped...]
VFS: brelse: Trying to free free buffer
Unable to handle kernel paging request at virtual address 00050040,
epc == 88041e7c, ra == 880464e0
Oops: 0000
$0 : 00000000 88140000 00000028 00000009
$4 : 00050028 00000001 bf0f0000 00000000
$8 : 00000720 00000000 00000000 00000000
$12: 00000008 000003e2 8836e59c 7ffffcf0
$16: 00050028 894c7c88 894c7d80 00000001
$20: 00000000 00000000 894c7c80 00000000
$24: 00000001 7ffffcf1
$28: 894c6000 894c7c58 00000000 880464e0
epc   : 88041e7c
Status: 3000fc03
Cause : 00000008

[and just another attempt to mkswap...]
VFS: brelse: Trying to free free buffer
Unable to handle kernel paging request at virtual address 00050040,
epc == 88041e7c, ra == 880464e0
Oops: 0000
$0 : 00000000 88140000 00000028 00000009
$4 : 00050028 00000001 bf0f0000 00000000
$8 : 00000720 00000000 00000000 00000000
$12: 00000008 000003e2 8836e59c 7ffffcf0
$16: 00050028 894c7c88 894c7d80 00000001
$20: 00000000 00000000 894c7c80 00000000
$24: 00000001 7ffffcf1
$28: 894c6000 894c7c58 00000000 880464e0
epc   : 88041e7c
Status: 3000fc03
Cause : 00000008

The same with recompiled mkswap.

Hope it helps.

I tried to compile our (international) ssh, but it ends with "not
enough memory" :( This indy has 32MB ram, maybe I will shut down our
web server and boot linux there, it has little bit more RAM and is
faster...
No, that's not goot idea :-(

david kostal ([email-masked])
----+
----- End of forwarded message from owner-linux@cthulhu -----

-- 
Peace, Ariel

---

From: Honza Pazdziora <[email-masked]>
Date: Wed, 17 Jun 1998 18:56:24 +0200 (MET DST)

> epc == 88041e7c, ra == 880464e0

OK, I once ( ;-) ) got to run the mkswap /dev/sdb2 OK. Before that
I tried dd if=/deb/sdb2 of=/dev/null bs=1024 count=1 and mkswap
/dev/sdb2 1024. These are two steps that lead to mkswap /dev/sdb2
without fail, creating 40 MB (correct) swap partition. I do not know
who caused it, whether that dd or that mkswap.

Now it seems that mkswap /dev/sdb2 35000 (eg with some size argument)
works fine. But I never got to make it work without the size parameter
again. David says that mkswap might have problems determining the size
of the partition. Also dd, when let to run over the whole device fails
with the same message about freeing free. But David says he was
successful running mkfs on that partition.

Weird, but I'm now happy it runs with something smaller (I do not know
(am lazy to find out) the exact size of the partition) swap.

In the meantime I played with swap into file and found some other
bugs. First, there are two swapon -a commands in rc.sysinit. When
I had that swapfile specified in /etc/fstab, it got swaponed twice.
Brrr. I had to do one swapoff to make it look normal.

Even if I had it only once (added manually) the machine was very
unhappy with the swapfile. Kswapd was taking a lot of CPU, the load
was growing and occassionally the machine was unusable -- too slow
that I had to resume to hard reset.

But as I say, with swap into the partition, it looks fine.

------------------------------------------------------------------------
 Honza Pazdziora | [email-masked] | http://www.fi.muni.cz/~adelton/
                   I can take or leave it if I please
------------------------------------------------------------------------