Re: [RFC,PATCH 11/15] knfsd: RDMA transport core

[Neil Brown <neilb@suse.de>]

On Friday May 18, tom@opengridcomputing.com wrote:
> On Fri, 2007-05-18 at 15:07 -0400, Trond Myklebust wrote:
> 
> > > +	while (xprt->sc_ctxt_cnt < target) {
> > > +		xprt->sc_ctxt_cnt ++;
> > > +		spin_unlock_irqrestore(&xprt->sc_ctxt_lock, flags);
> > > +
> > > +		ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
> > > +
> > > +		spin_lock_irqsave(&xprt->sc_ctxt_lock, flags);
> > 
> > You've now dropped the spinlock. How can you know that the condition
> > xprt->sc_ctxt_cnt <= target is still valid?
> > 
> 
> I increment the sc_ctxt_cnt with the lock held. If I'm at the limit, the
> competing thread will find it equal -- correct? 
> 

I'm having trouble figuring out who the competing thread is.
As far as I can see (Well... "have seen"), this is always called from
the context of an nfsd thread which has sole access to the xprt.  So
there is no race.
??

NeilBrown

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