Re: umount -f stalls forever

[NeilBrown <neilb@suse.de>]

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On Wed, 09 Jul 2014 14:15:03 -0600 Nathan Shearer <mail@nathanshearer.ca>
wrote:

> When I have an nfs share that is mounted with the hard option (either
> explicitly or implicitly since hard is on by default), and the nfs
> server becomes unresponsive for any reason, it often causes the entire
> OS to hang on many operations. In some cases I cannot even reboot a
> server depending on what the nfs share was used for.
> 
> I relaize that this was probably done intentionally to prevent data
> loss. However, when I am cleaning up a disaster and I actually do want
> to "umount -f" a stalled nfs share and data loss es acceptable, then I
> expect that command to return and the share to be unmounted. From a
> usability perspective, stalling forever when I am explicitly forcing an
> action is not right.
> 
> There is a workaround: and that is to assign the IP of the nfs server to
> my system then issue umount -f, however that hardly the best way since I
> am changing my network topology to unmount an offline filesystem. In
> some situations adding an IP to an interface is not possilble, and if
> the system is a remote system it could lead to more problems since it is
> mostly unresponsive.
> 
> It would be greatly appreciated if a patch could be introduced that
> allows "umount -f" to actually work without making any other changes to
> a running system. The man page for umount even states that the -f
> argument can be used to unmount an unreachable nfs share -- but it
> almost never works.
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Hi Nathan,
 you don't say what kernel you are running....

 A change was made in Linux 3.12 (8033426e6bdb2690d302872ac1e1fadaec1a5581)
 which may address the problem you have.
 So if you are using a kernel older than that, try a newer kernel.
 This may not make "umount -f" work, but it should stop it from hanging.
 To make it work you might need to kill all the processes using the mount
 point first.

 Also, "umount -l" might be a suitable answer to your problems.

NeilBrown

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