Hi Bruce,
Thanks for the clarification.
(I'm repeating a lot of my original mail because of the Cc: list.)
> J. Bruce Fields
> I think that's right, though I'm curious how you're managing to hit
> that case reliably every time. Or is this an intermittent failure?
It's an intermittent failure, but with the procedure shown below it is
fairly easy to reproduce. The actual problem we see in our product
is because of the way external storage media are handled in user-land.
192.168.1.10# mount -t xfs /dev/sdcr/sda1 /mnt
192.168.1.10# exportfs 192.168.1.11:/mnt
192.168.1.11# mount 192.168.1.10:/mnt /mnt
192.168.1.11# umount /mnt
192.168.1.10# exportfs -u 192.168.1.11:/mnt
192.168.1.10# umount /mnt
umount: can't umount /media/recdisk: Device or resource busy
What I actually do is the mount/unmount on the client via ssh. That
is a good way to trigger the problem.
We see that during the un-export the NFS caches are not flushed
properly which is why the final unmount fails.
In net/sunrpc/cache.c the cache times (last_refresh, expiry_time,
flush_time) are measured in seconds. If I understand the code somewhat
then during an NFS un-export the is done by setting the flush_time to
the current time. The cache_flush() is called. If in that same second
last_refresh is set to the current time then the cached item is not
flushed. This will subsequently cause un-mount to fail because there
is still a reference to the mount point.
> J. Bruce Fields
> I ran across that recently while reviewing the code to fix a related
> problem. I'm not sure what the best fix would be.
>
> Previously raised here:
>
> http://marc.info/?l=linux-nfs&m=133514319408283&w=2
The description in your mail does indeed looks the same as the problem
that we see.
>From reading the code in net/sunrpc/cache.c I get the impression that it is
not really possible to reliably flush the caches for an un-exportfs such
that after flushing they will not accept entries for the un-exported IP/mount
point combination.
With kind regards,
Hans Zuidam
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