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Old 05-04-2010, 06:57 PM
Kees Cook
 
Default revert work-around for bug 543617 please

Hello,

I think that 5e1941884c700b7b97bcad52c2d8212ac56a7ebc is causing more
problems than it tries to solve[1]. i.e. if any filesystem is under heavy
load, you can't umount any other filesystems until the sync finishes.

Additionally, trivial stuff (even with an idle system) take an unexpectedly
long time (e.g. umount of a bind mount takes 1 second instead of nearly 0).

Try this in Karmic and Lucid:

sudo -s
mkdir -p /mnt/test
mount -o bind /tmp /mnt/test
time umount /mnt/test

Karmic: real 0m0.010s
Lucid: real 0m1.022s

-Kees

[1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/543617

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Kees Cook
Ubuntu Security Team

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Old 05-05-2010, 12:10 PM
Andy Whitcroft
 
Default revert work-around for bug 543617 please

On Tue, May 04, 2010 at 11:57:19AM -0700, Kees Cook wrote:
> Hello,
>
> I think that 5e1941884c700b7b97bcad52c2d8212ac56a7ebc is causing more
> problems than it tries to solve[1]. i.e. if any filesystem is under heavy
> load, you can't umount any other filesystems until the sync finishes.
>
> Additionally, trivial stuff (even with an idle system) take an unexpectedly
> long time (e.g. umount of a bind mount takes 1 second instead of nearly 0).
>
> Try this in Karmic and Lucid:
>
> sudo -s
> mkdir -p /mnt/test
> mount -o bind /tmp /mnt/test
> time umount /mnt/test
>
> Karmic: real 0m0.010s
> Lucid: real 0m1.022s
>
> -Kees
>
> [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/543617

I believe Surbhi is now testing a potential upstream fix. If that
testing is good, then we would clearly revert and replace it. I am
therefore inclined to wait on that testing, rather than jump the SRU
process twice.

Otherwise it does appear that this has a not so healthy side.

-apw

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