[SMP] 2.4.5-ac13 through ac18 dcache/NFS conflict

From: Bob Glamm (glamm@mail.ece.umn.edu)
Date: Fri Jun 29 2001 - 11:21:00 EST

Just to follow up on this situation, I think I've tracked it down
to a problem arising from a combination of SMP, the directory entry
cache, and NFS client code. After several 24-hour runs of 10 copies

  'find /nfs-mounted-directory -print > /dev/null'

running simultaneously, the kernel stops or dies in fs/dcache.c
(in dput() or d_lookup(), and it triggered the BUG() on
line 129 once).

Performing the same 10 finds on a locally mounted ext2 filesystem
produces no lockups or hangs.


> I've got a strange situation, and I'm looking for a little direction.
> Quick summary: I get sporadic lockups running 2.4.5-ac13 on a
> ServerWorks HE-SL board (SuperMicro 370DE6), 2 800MHz Coppermine CPUs,
> 512M RAM, 512M+ swap. Machine has 8 active disks, two as RAID 1,
> 6 as RAID 5. Swap is on RAID 1. Machine also has a 100Mbit Netgear
> FA310TX and an Intel 82559-based 100Mbit card. SCSI controllers
> are AIC-7899 (2) and AIC-7895 (1). RAM is PC-133 ECC RAM; two
> identical machines display these problems.
> I've seen three variations of symptoms:
> 1) Almost complete lockout - machine responds to interrupts (indeed,
> it can even complete a TCP connection) but no userspace code gets
> executed. Alt-SysRq-* still works, console scrollback does not;
> 2) Partial lockout - lock_kernel() seems to be getting called without
> a corresponding unlock_kernel(). This manifested as programs such
> as 'ps' and 'top' getting stuck in kernel space;
> 3) Unkillable programs - a test program that allocates 512M of memory
> and touches every page; running two copies of this simultaneously
> repeatedly results in at least one of the copies getting stuck
> in 'raid1_alloc_r1bh'.
> Symptom number 1 was present in 2.4.2-ac20 as well; symptoms 2 and 3
> were observed under 2.4.5-ac13 only. I never get any PANICs, only
> these variety of deadlocks. A reboot is the only way to resolve the
> problem.
> There seem to be two ways to manifest the problem. As alluded to in
> (3), running two copies of the memory eater simultaneously along with
> calls to 'ps' and 'top' trigger the bug fairly quickly (within a minute
> or two). Another method to manifest the problem is to run multiple
> copies of this script (I run 10 simultaneous copies):
> #!/bin/sh
> while /bin/true; do
> ssh remote-machine 'sleep 1'
> done
> This script causes (1) in about a day or two.
> If anyone has any suggestions about how to proceed to figure out what
> the problem is (or if there is already a fix), please let me know.
> I would be more than willing to provide a wide range of cooperation on
> this problem. I don't have a feel for where to go from here, and I'm
> hoping that someone with more experience can give me some
> assistance..
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This archive was generated by hypermail 2b29 : Sat Jun 30 2001 - 21:00:22 EST