umount hangs with initramfs as root

[Rob Landley]

On Tuesday 21 March 2006 4:35 pm, Chuck Meade wrote:
> Busybox umount hangs when I try to reboot, while running on a root
> fs which is an initramfs.  Reboot is configured on my system to
> "umount -a -r", and the umount of the initramfs root is hanging.

You're using a kernel before 2.6.13, aren't you?

I forgot: the patch to prevent initramfs from being umounted went in around 
then.  Before that you could hang your system hard by umounting initramfs.  
(The kernel would go into an endless loop since the mount list is a circular 
doubly linked list with initramfs as the start/end point it searches for.)

Hmmm...  Didn't test umount -a with an older kernel.

> I have searched the web for the solution, but most of the hits for
> this problem are from people trying to switch from their initramfs to
> their "real" root fs - thus they have done a switch_root, and they
> just need to take certain steps to correct their procedure to be able
> to umount the initramfs.  I am *not* attempting to switch_root or
> pivot_root, but rather to *reboot* from a system running with a root
> that is an initramfs.  Reboot is umounting the initramfs, without having
> switched to a different root.
>
> Is this a known issue?  Is there a fix?  Has this been addressed before
> (perhaps even in the latest "mount" work Rob has been doing)?

I tweaked umount a bit, but it's possible this specific issue didn't get 
addressed.

What versions of busybox and the kernel are you using?  I'll see if I can 
reproduce it.  Is this a recent problem, or has busybox been doing it for a 
while?

> Thanks for whatever info you can provide,
> Chuck

Rob

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