The "unmount of /dev failed (BUSY)" message, explained
Tyler Gee
geekout at gmail.com
Sun May 8 00:44:02 PDT 2005
Nice, good work. I had been wondering about that one...
On 5/8/05, Andre Guibert de Bruet <andy at siliconlandmark.com> wrote:
> Folks,
>
> In a show of way too much free time, I set off on a quest to figure out
> what was up with the "unmount of /dev failed (BUSY)" message that is seen
> on reboot. I am pleased to announce that I found what I believe to be the
> reason behind the message:
>
> vfs_unmountall: Processing /dev/amrd1a:
> vfs_unmountall: Processing /dev/amrd0s1d:
> vfs_unmountall: Processing /dev/amrd0s1f:
> vfs_unmountall: Processing /dev/amrd0s1e:
> vfs_unmountall: Processing devfs:
> 0xc53efcc0: tag devfs, type VCHR
> usecount 1, writecount 0, refcount 22 mountedhere 0xc53d4c00
> flags ()
> v_object 0xc10608c4 ref 0 pages 72
>
> dev amrd0s1a
> 0xc5442550: tag devfs, type VCHR
> usecount 1, writecount 0, refcount 1 mountedhere 0xc53d4b00
> flags ()
>
> dev amrd0s1b
> unmount of /dev failed (BUSY)
> vfs_unmountall: Processing /dev/amrd0s1a:
> 0xc53efaa0: tag ufs, type VDIR
> usecount 1, writecount 0, refcount 1 mountedhere 0xc5396800
> flags ()
>
> ino 32896, on dev amrd0s1a
> 0xc53ef880: tag ufs, type VREG
> usecount 3, writecount 0, refcount 5 mountedhere 0
> flags (VV_TEXT)
> v_object 0xc1060738 ref 2 pages 89
>
> ino 16527, on dev amrd0s1a
> Uptime: 12m8s
>
> The patch that produces this output is available from:
> http://bling.properkernel.com/freebsd/vfs_unmountalldiag.diff
>
> As you can see from the output, the unmount of /dev fails because the
> /dev/amrd0s1a (Which is the root mountpoint on this system) and
> /dev/amrd0s1b (Primary swap) device nodes still exist. The logic that we
> have that uses reverse TAILQ unmounting is flawed because the root
> filesystem is mounted read-only before devfs.
>
> I will be cleaning up my patch a bit before I submit it to be committed. I
> will also be producing a patch that will make vfs_unmountall do the right
> thing.
>
> I haven't found a way to make it vacuum my apartment yet but I will submit
> that functionality to ACME Labs when it's available... ;-)
>
> Andy
>
> PS: If you want to cross-reference the filesystems, the list is here:
> http://bling.properkernel.com/freebsd/fstab
>
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