Why won't 8.2 umount -f?

Doug Barton dougb at FreeBSD.org
Tue Feb 14 02:41:14 UTC 2012

On 02/13/2012 18:23, Rick Macklem wrote:
> Doug Barton wrote:
>> Is there some magic I'm missing to convince an 8.2 system to umount
>> -f?
>> I had an NFS server crash, so I'm trying to get the mounts updated.
>> All
>> of the 7.x systems happily did 'umount -f', but the 8.x systems
>> (mostly
>> 8.2-pN) are just hanging forever.
>> Is this a bug, or is it something I'm missing?
> Well, I didn't realize that a 7.n system would "umount -f" an NFS
> mount when the server was down and there were dirty blocks that
> needed to be written back, but I don't know.

I'm doubtful that any of those systems had dirty blocks.

> (I seem to recall that
> someone encouraged me to MFC one of my changes related to this back
> to stable/7, but I'm not sure if it mattered?)

Please don't unless you can verify that it doesn't make this situation
worse. :)

> I have pretty well fixed the new client w.r.t. this except for the
> case where you do a "umount <path>" and that gets hung. Once a non "-f"
> umount gets hung, there is nothing you can do, because the mount point is
> locked up, so a subsequent "umount -f" can't get as far as nfs_umount().

I'm aware of this issue, and I did 'umount -f' first. But I wonder if
this isn't something that should be fixed because I think most users
would expect that 'umount -> umount -f' would be the natural
progression, similar to 'kill -> kill -9'.

> My guess is that the old (default for 8.n) client isn't fixed for
> this. If you "grep MNTK_UNMOUNTF" in the sources, you'll see it
> used some in the old/regular client, but not as much as the new one.
> You also need a fairly recent (can't remember if that is in 8.2)
> version of umount.c, since the code had a "sync();" at the beginning
> of it that would hang before even getting to the umount(2) syscall.
> Bottom line, I think the newnfs client (the default for 9.0) can
> do this, but I'm doubtful the old/reguler one can. (I also wouldn't
> be surprised if there is still a bug other than the above mentioned
> one w.r.t. doing a "umount /mnt" and getting that hung before trying
> "umount -f /mnt".

Is the new client in 8-stable up to date relevant to 9.0, and/or is it
considered safe to use in production?




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