linux-kernel - Re: [V9fs-developer] [PATCH 2/6] 9p: Replace the fidlist with an IDR

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Date:   Wed, 11 Jul 2018 05:52:19 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Dominique Martinet <asmadeus@...ewreck.org>
Cc:     v9fs-developer@...ts.sourceforge.net,
        Latchesar Ionkov <lucho@...kov.net>,
        Eric Van Hensbergen <ericvh@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Ron Minnich <rminnich@...dia.gov>
Subject: Re: [V9fs-developer] [PATCH 2/6] 9p: Replace the fidlist with an IDR

On Wed, Jul 11, 2018 at 02:40:38PM +0200, Dominique Martinet wrote:
> Matthew Wilcox wrote on Thu, Jun 28, 2018:
> > diff --git a/net/9p/client.c b/net/9p/client.c
> > index f8d58b0852fe..bbab82f22c20 100644
> > --- a/net/9p/client.c
> > +++ b/net/9p/client.c
> > @@ -908,30 +908,27 @@ static struct p9_fid *p9_fid_create(struct p9_client *clnt)
> > -	ret = p9_idpool_get(clnt->fidpool);
> > -	if (ret < 0)
> > -		goto error;
> > -	fid->fid = ret;
> > -
...
> > +	idr_preload(GFP_KERNEL);
> > +	spin_lock_irq(&clnt->lock);
> > +	ret = idr_alloc_u32(&clnt->fids, fid, &fid->fid, UINT_MAX, GFP_NOWAIT);
> 
> There's also a P9_NOFID that we shouldn't use, so the max here should be
> P9_NOFID - 1

Happy to fix that.  It shouldn't actually happen, of course.  I can't
imagine us having 4 billion FIDs in use at once.

> That aside this introduces a change of behaviour that fid used to be
> alloc'd linearily from 0 which no longer holds true, that breaks one
> serveur (nfs-ganesha just returns ERANGE) but others seem to handle this
> just fine so they'll just need to fix that server.
> max aside this looks good.

I don't understand your assertion that this is a change of behaviour.
The implementation of p9_idpool_get() uses idr_alloc(), not
idr_alloc_cyclic(), so I don't believe I've changed which FID would
be allocated.