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Bug#483830: marked as done (Writing to a filesystem mounted with 'loop' don't work)

Your message dated Sun, 8 Feb 2009 11:28:21 +0100
with message-id <20090208102821.GA3574@galadriel.inutil.org>
and subject line Re: your mail
has caused the Debian Bug report #483830,
regarding Writing to a filesystem mounted with 'loop' don't work
to be marked as done.

This means that you claim that the problem has been dealt with.
If this is not the case it is now your responsibility to reopen the
Bug report if necessary, and/or fix the problem forthwith.

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483830: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=483830
Debian Bug Tracking System
Contact owner@bugs.debian.org with problems
--- Begin Message ---
Package: linux-image-2.6.18-5-486
Version: 2.6.18.dfsg.1-13etch5
Severity: important

When writing into a filesystem mounted using the 'loop' module, the system have unexpected behaviours.

Tested with:
2 different Debian Etch running servers, up to date (one Core2Duo and one AMD 4200+).
Linux Mint 4.0 personnal computer, up to date (AMD 4000+).
Debian Etch i386 fresh install, no updates. Then up to date (AMD 4200+).
Debian Etch AMD64 fresh install, no updates. Then up to date (AMD 4200+).
Debian Lenny i386 frsh install, no updates. Then up to date (AMD 4200+).

Fedora 9 Live: don't have the bug.
Thus the bug seems to be related to Debian only.

How to reproduce the problem:

WARNING: don't do it on a remote computer because the system could completly stop responding.

as root:

# modprobe loop
# cd ~
# mkdir test
# cd test

# dd if=/dev/zero of=virtualdisk bs=1M count=2000
--> 53 Mb/s

# losetup /dev/loop0 virtualdisk

# mkfs.ext2 /dev/loop0
--> one system was frozen here once
# mount /dev/loop0 /mnt

# dd if=/dev/zero of=/mnt/bigfile bs=1M
--> the file start growing then nothing happens
--> this process never ends
--> ctrl+C works after 5 to 15 seconds
--> on some systems the computer stop responding
--> on some systems some bytes are written to the file every 20 to 40 seconds

From another console we can see a strange iowait:

# iostat -m 1

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           0,50    0,00    0,00   50,00    0,00   49,50

Device:            tps    MB_read/s    MB_wrtn/s    MB_read    MB_wrtn
sda               0,00         0,00         0,00          0          0

The size of /mnt/bigfile is between 50 Mb and 400 Mb. The size seems to always be the same on one computer, but vary from computer to computer. i.e. on computer 'A' the file is between 50 Mb and 55 Mb, on computer 'B' the file is between 300 Mb and 310 Mb.

Even a simple write without mounting anyfilesystem is affected on some systems:
# dd if=/dev/zero of=/dev/loop0 bs=1M
--> 14 Mb/s  (4 times slower than bare metal speed)

--- End Message ---
--- Begin Message ---
Version: 2.6.26-1

On Sun, Nov 23, 2008 at 11:33:21AM +0100, Moritz Muehlenhoff wrote:
> On Fri, Nov 21, 2008 at 01:31:24PM -0500, Xavier Douville wrote:
> > Hi
> > 
> > I have not been able to reproduce this bug, at least not with 2.6.26
> > (which is also the kernel used by Fedora Core 9)
> > 
> > dd if=/dev/zero of=/mnt/bigfile bs=1M
> > 
> > This process ends after filling the 2GB loop device on my laptop (Debian
> > testing)
> > 
> > ctrl+C does take 15 sec but I am not sure if it's a bug. It's instant
> > when not doing the command as root.
> > 
> > I don't have root access on FC9 machines here so I can't compare it.
> > 
> > iostat returns a valid speed (arround 20 MiB/s)
> David, can you confirm that it's fixed with the current Lenny kernel?

Marking as fixed in 2.6.26, please reopen if the problem persists.


--- End Message ---

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