Red Hat Bugzilla – Bug 68673
Kernel hangs when using loopback device
Last modified: 2008-08-01 12:22:52 EDT
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User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.0; Q312461)
Description of problem:
I'm using kernel (2.4.18-5smp).
When I have applied heavy load to loopback device, a kernel will hang-up.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. dd if=/dev/zero of=test.img bs=1024k count=1024
2. losetup /dev/loop1 test.img
3. mke2fs -j /dev/loop1
4. mkdir /mnt/test
5. mount /dev/loop1 /mnt/test
6. cd /mnt/test
7. iozone -a
(iozone can download from http://www.iozone.org )
Actual Results: The reaction of a console is lost.
Ctrl + alt + delete key reset is also ineffective.
kernel hang up.
Expected Results: It is that a benchmark tool (iozone) is completed with no
In the case of 2.4.18-4smp, it becomes as expected.
Ok we didn't actually change loop between -4 and -5
however is sysreq-t possible ?
(and if keyboard REALLY doesn't respond, please try adding nmi_watchdog=1 to the
vmlinuz line in /boot/grub/grub.conf)
(One year later...)
This old, unresolved bug describes my problem exactly. I am using Red
Hat 9 with 2.4.20-20.9smp. I also tried it with 2.4.20-19.9 in single
processor mode. I set nmi_watchdog=1. The system always hangs, 100%
As the original poster did, I created a script to isolate the problem.
When I run the fatal script under Gnome, the system simply freezes and
does not respond to anything. When I run the script from a console,
the system responds to "console switch" function keys. Typed
characters are echoed on the screen, though no higher functioning
(switching to the Gnome window leads to a black, unresponsive screen).
Machine details: 2.6 GHz P-4, 1 Gb RAM, 500 Mb swap.
My script follows. I coded a loop to emulate the backup-to-CD utility
that uncovered the bug. The system always hangs during the first copy.
I use large file sizes because that's what originally triggered the
hang. Smaller files (not sure how much smaller) successfully copied to
the loop device.
# Demonstrates a loop device kernel hanging bug.
# 2 Gb free space in current directory.
# Loop device 0 is /dev/loop0.
# Run script as root.
echo "Initialize virtual partition ..."
rm -rf vpartvmnt data
dd if=/dev/zero of=vpart bs=1M count=714
losetup /dev/loop0 vpart
mke2fs -q -m 0 -b 2048 /dev/loop0
mount -o dev,suid /dev/loop0 vmnt
rm -rf vmnt/*
echo "Initialize test data ..."
dd if=/dev/urandom of=data bs=1M count=225
while (true); do
echo "Copying data.$I ..."
cp data vmnt/data.$I
if [ $? != 0 ]; then
echo "Overflow. Removing data.$I ..."
rm -f vmnt/data.$I
Thanks for the bug report. However, Red Hat no longer maintains this version of
the product. Please upgrade to the latest version and open a new bug if the problem
The Fedora Legacy project (http://fedoralegacy.org/) maintains some older releases,
and if you believe this bug is interesting to them, please report the problem in
the bug tracker at: http://bugzilla.fedora.us/