[unionfs] deadlocking a 9-STABLE machine with two unionfs mounts onto the same mountpoint

[Alexander Yerenkow]

2015-02-09 16:22 GMT+02:00 Andre Albsmeier <andre at fbsd.ata.myota.org>:

> Retrying here as -fs didn't show up any results...
>
> ----- Forwarded message -----
>
> I can reliably deadlock a 9.3-STABLE by the following procedure:
>
> Let's assume that /tmp is a standard swap-backed file system
> already. First let's set up what we need:
>
> mkdir /tmp/1 /tmp/2
> mount -v -t unionfs /tmp/1 /usr/local
> mount -v -t unionfs /tmp/2 /usr/local
>

Few years ago case was even simplier
mkdir /tmp/1
mount -v -t unionfs /tmp/1 /usr/local
#yep, just twice mount
mount -v -t unionfs /tmp/1 /usr/local
ls /tmp/1
#and the shell hangs.



>
> No let's lock the system:
>
> mkdir /tmp/2/bla
> while :; do
>   echo go
>   tar -cC /usr/src/etc -f - . | tar -xpC /tmp/2/bla -f -
> done
>
> It survives about 3 or 4 rounds, sometimes more, sometimes
> only 2. It is important to use tar to copy the stuff. If
> we replace the tar line by e.g.
>
> cp -pR /usr/src/etc/* /tmp/2/bla
>
> things are all well.
>
> The system doesn't lock up entirely, you can move the mouse
> and ping it but no fs access is possible anymore. One can
> switch to the console and enter the debugger but a reboot
> with ctrl-alt-del doesn't work...
>
> The interesting part is that all this worked pretty well on
> 9-STABLE until approx. 2 months ago. But nothing had been
> committed to unionfs for a long time so I really have no
> idea what's going on.
>
> It also reminds us of
>
> https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=161511
>
> but this stuff had been merged to 9-STABLE already...
>
> Anything I can do to get this fixed?
>
> ----- End forwarded message -----
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-- 
Regards,
Alexander Yerenkow