Subject: Re: [RFC] add rtnl semaphore to linux-atm

From: Mitchell Blank Jr <[email-masked]>
Date: Fri, 3 Oct 2003 22:55:26 -0700

David S. Miller wrote:
> > We *can't* use it to protect the state of the vcc list though because we
> > need to do lookups in both interrupt and bh context.  Using a sleeping
> > lock alone is a non-starter.
> > 
> > That's why we need to do the three-step spinlock->semaphore->spinlock
> > dance in the vcc open and close paths.
> 
> The semaphore protects "modifications", it basically serializes them.
> 
> You still need a rwlock to protect the actual lists and this rwlock
> is what the interrupt/bh context code takes to traverse the lists
> and tables.

I think we're saying approximately the same thing at this point.

I'm just trying to make the point that the spinlock (or rwlock, whatever)
can't be held when we call atm_dev->{open,close}() since they can sleep.
Which is why we need to do the three-step process I described in the
earlier email.

Once you do that there's no reason (that I know of) to take rtnl_sem
except to serialize the actual calls into atm_dev's ops.  There's no
problem if multiple opens both get their vpi/vci's allocated in
"inactive" state as long as the actual connects happen in series.

-Mitch