Re: The "unmount of /dev failed (BUSY)" message, explained

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
> 
> /*  Andre Guibert de Bruet  * 6f43 6564 7020 656f 2e74 4220 7469 6a20 */
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