Re: Hanging at shutdown with mystery "file system full" error

["Ian D. Leroux" <idleroux%fastmail.fm@localhost>]

On Thu, 22 Oct 2015 13:57:25 +0700 Robert Elz <kre%munnari.OZ.AU@localhost> wrote:

>     Date:        Thu, 22 Oct 2015 07:52:06 +0200
>     From:        "Ian D. Leroux" <idleroux%fastmail.fm@localhost>
>     Message-ID:  <20151022075206.995f2caa63b153174b7f7ead%fastmail.fm@localhost>
>   | How are tmpfs filesystems special in this regard?
> 
> Well....
> 
> The problem is that it is permitted to swap onto files.   If we did
> away with that, there would be no problems to solve.
>
> [detailed and patient explanation of the interaction between tmpfs
> filesystems and file-backed swap]

Thanks!  That helped a lot.

>   | That sounds to me like there are several possibly-unrelated
>   | shutdown hangs,
> 
> Could be ... or it is also possible that the /dev problem and no space
> message you're seeing are co-incidental. and while annoying, not
> actually related to the hang you're seeing.

Ok, so let's separate the issues.

1- With tmpfs-mounted /dev, /etc/rc.d/swap1 attempts to umount -f /dev
before userland is finished at shutdown time.  Whether or not this
causes the hang and error message I see, this is clearly not a desirable
outcome.  I think we understand what the problem is, and there are
workarounds for my case and most others I can think of, although it's
not clear what the right general fix is.  I'll file a PR for this, and
further discussion can go there or in another thread.

2- The system will sometimes hang after printing a kernel error message
of the general form "on /var: file system full", despite the fact
that /var is not full and that the immediate trigger for the hang, at
least in my case and apparently also in the case of Robert Swindells,
is unmounting a tmpfs filesystem that has nothing to do with /var.

To investigate the second  issue we need a way of triggering the hang
that is not as manifestly crazy as removing /dev, which seems to be the
only way I've ever triggered it (Robert Swindells seems to have found
another way, though it's not clear what).  I'll try populating an
on-disk /dev and then seeing if I still get a hang at shutdown.

--
IDL