Re: Finding an available fss device

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

On Sun, Aug 12, 2018 at 10:16:48AM +0200, J. Hannken-Illjes wrote:
> While creating a snapshot "/mount0" lookup "/mount0/file", it will block
> as "/mount0" is suspended.  The lookup holds a lock on "/".
> 
> Now snapshot "/ "and trying to suspend "/" will block as the lookup
> has the root vnode locked.

This scenario is not the same as the one I asked about, which
was: performing a snapshot of filesystem mounted on /mount0 
using /dev/fss0 and a snapshot of filesystem mounted on /mount1
using /dev/fss1 while the first one is still active. Is there some
deadlock in this case?

But you also raise a deadlock scenario for which there is no
protection in currentn code. I already experienced it in the
past and it would be fair to return EGAIN rather than letting the
administrator set a snapshot that will kill the system later.

-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost