Re: losetup -d --force for zombie loop devices?

[Phillip Susi <psusi@ubuntu.com>]

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On 01/11/2013 06:52 PM, Mike Frysinger wrote:
> On Thursday 03 May 2012 10:29:07 Phillip Susi wrote:
>> If you want to hide mounts from certain processes, that is what
>> unshare is for.  Hiding a mount from all processes does not make
>> sense.  If you know a mount is gone and beyond recovery ( like in
>> this loop over nfs case, or removed media ), then it should be
>> forcibly unmounted, not simply made invisible and doomed to
>> remain a zombie mount until the system is rebooted.
> 
> in an ideal world, maybe unshare might work.  in the real world, it
> doesn't. you can use it only on *new* processes, not ones that are
> already running. nor can you do `unshare shutdown` and have it work
> since that simply signals a long running init process to initiate a
> shutdown.
> 
> an nfs server goes afk and attempts to `umount` it timeout, as well
> as many desktop programs (like kde io daemons that like to walk
> available mount points) or shutdown processes.  no call to
> `unshare` will fix this, but certainly forcibly removing it with
> `umount -l` will. -mike

A bit of a delayed response there, but my point was that what you are
looking for is umount -f, not umount -l.  It also used to be that once
you detached a mount with umount -l, you could not reattach it.
Attempts to remount would fail with EBUSY and so this was a horribly
broken state to be in.  At some point it seems this was changed and
now you *can* reattach, so lazy unmount is no longer pure evil, but
still it is no forced unmount.


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