Re: XFS filesystem claims to be mounted after a disconnect

[Dave Chinner <david@fromorbit.com>]

On Mon, Jun 02, 2014 at 02:22:15PM +0300, Martin Papik wrote:
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> >> How can I detect this situation? I mean I didn't see anything in 
> >> /proc/mounts or references to the mount point from /proc/<pid>/*,
> >> so I only managed to correct it (chdir elsewhere) by chance on a
> >> hunch. Would it not be desirable to know that there's a phantom
> >> FS referenced by a number of processes?
> > 
> > lsof.
> 
> No good.

lsof reports such things as belonging to / because it can't find the
correct path for them. Indeed, you can't find them by filtering on
mount point, file or anything else. But they are there.

e.g:

$ sudo mount /dev/vdc /mnt/scratch
$ cd /mnt/scratch
$ sudo umount -l /mnt/scratch
$ sleep 300
$ cd ~
$ ps -ef |grep [s]leep
dave     16341  7432  0 09:27 pts/1    00:00:00 sleep 300
$ sudo lsof |grep sleep
sleep     16341            dave  cwd       DIR             253,32        6         96 /
sleep     16341            dave  rtd       DIR                8,1     4096          2 /
sleep     16341            dave  txt       REG                8,1    31208      32607 /bin/sleep
sleep     16341            dave  mem       REG                8,1  1742520     245384 /lib/x86_64-linux-gnu/libc-2.17.so
sleep     16341            dave  mem       REG                8,1   145160     245381 /lib/x86_64-linux-gnu/ld-2.17.so
sleep     16341            dave  mem       REG                8,1  1607584      98063 /usr/lib/locale/locale-archive
sleep     16341            dave    0u      CHR              136,1      0t0          4 /dev/pts/1
sleep     16341            dave    1u      CHR              136,1      0t0          4 /dev/pts/1
sleep     16341            dave    2u      CHR              136,1      0t0          4 /dev/pts/1

See the first two DIR lines? They have different devices but the
same path (/). That's what you need to look for - the non-root device
with a root path - in this case 253,32:

$ ls -l /dev/vdc
brw-rw---- 1 root disk 253, 32 Jun  3 09:01 /dev/vdc
$

With this knowledge, the simple way:

$ sudo lsof |grep "253,32"
bash       7432            dave  cwd       DIR             253,32        6         96 /
sleep     16341            dave  cwd       DIR             253,32        6         96 /

There's the two processes  holding references to the unmounted
filesystem.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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