linux 2.2.18pre17 + VM-global -7 = `Negative d_count' oops

From: Ian Jackson (ijackson@chiark.greenend.org.uk)
Date: Thu Oct 26 2000 - 12:37:37 EST


Andrea Arcangeli writes ("Re: linux 2.2.18-pre17: "Kernel panic: LRU list corrupted""):
> I also included the fix in a new VM-global patch against vanilla 2.2.18pre17
> (the VM-global patch is available as a single patch inside 2.2.18pre17aa1/
> directory too but I have to maintain a separate version of it against clean
> 2.2.18pre17 due silly rejects that I can't avoid)
>
> ftp://ftp.us.kernel.org/pub/linux/kernel/people/andrea/patches/v2.2/2.2.18pre17/VM-global-2.2.18pre17-7.bz2

I've been having apparently VM-related `pauses' with 2.2.17 [1], so I
thought I'd try 2.2.18pre17 with that patch. The results weren't
good: I get many instances of

 Negative d_count (-805538369) for [binary garbage]/<NULL>

followed by an oops. Kernel logfile extract below, uuencoded.

I'm sure I'd be able to reproduce this, but I'd rather not because
this is a production system. ver_linux reports:

chiark:linux-2.2.17-chiark> sh scripts/ver_linux
-- Versions installed: (if some fields are empty or looks
-- unusual then possibly you have very old versions)
Linux chiark 2.2.17 #2 Thu Oct 26 10:57:45 BST 2000 i586 unknown
Kernel modules 2.3.11
Gnu C 2.95.2
Binutils 2.9.5.0.37
Linux C Library 2.1.3
Dynamic linker ldd: version 1.9.11
Procps 2.0.6
Mount 2.10f
Net-tools 2.05
Kbd 0.99
Sh-utils 2.0
cat: /proc/modules: No such file or directory
Modules Loaded
chiark:linux-2.2.17-chiark>

I don't know why it says `Kernel modules 2.3.11', since I have
disabled kernel modules completely. My CPU is:

processor : 0
vendor_id : AuthenticAMD
cpu family : 5
model : 8
model name : AMD-K6(tm) 3D processor
stepping : 0
cpu MHz : 350.808
cache size : 64 KB
fdiv_bug : no
hlt_bug : no
sep_bug : no
f00f_bug : no
coma_bug : no
fpu : yes
fpu_exception : yes
cpuid level : 1
wp : yes
flags : fpu vme de pse tsc msr mce cx8 sep mmx 3dnow
bogomips : 699.60

REPORTING-BUGS wanted me to include /proc/scsi/scsi, so here it is:

Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
  Vendor: IBM Model: DCAS-34330 Rev: S65A
  Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 02 Lun: 00
  Vendor: IBM Model: DCAS-34330 Rev: S65A
  Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 04 Lun: 00
  Vendor: HP Model: T20 Rev: 3.01
  Type: Sequential-Access ANSI SCSI revision: 02
Host: scsi1 Channel: 00 Id: 00 Lun: 00
  Vendor: IBM Model: DNES-318350W Rev: SA30
  Type: Direct-Access ANSI SCSI revision: 03

It might be relevant that a large part of the system's job is to be a
shell account server, and users log in with a variety of mechanisms,
most often OpenSSH (Debian 1.2.3-9). I've not had any reports from
users about sessions randomly dropping, which I might have expected;
however, I did have a number of background cron jobs die in very
strange ways suggesting killing of processes at random.

The system as a whole is largely Debian 2.2, and has 256Mb of RAM and
about 400Mb of swap. It usually runs with about 50-100Mb of swap used
and at a load of somewhere around 1ish during busy periods.

[1] VM lockup problem:

I believe that this is a known problem with the 2.2.x VM ? The
symptoms I have are that under reasonably high but not excessive VM
and/or disk load, the system will freeze for around 10-15 minutes.
Most often this seems to have beeen provoked by a moderately large
(20Mb or so) Emacs doing an auto-save during an otherwise-busy time.

During the lockup network packets are processed - pings receive
replies, and TCP connection attempts succeed, but there is no evidence
of any user-mode executing. After the lockup the system apparently
just resumes where it left off. Sometimes afterwards there is a
message like `VM: do_try_to_free_pages failed for emacs...' but more
often there isn't.

Thanks for your attention,

Ian.

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