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

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Date:   Wed, 11 Jul 2018 14:58:12 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Matthew Wilcox <willy@...radead.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

Matthew Wilcox wrote on Wed, Jul 11, 2018:
> On Wed, Jul 11, 2018 at 02:40:38PM +0200, Dominique Martinet wrote:
> > > +	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.

Oh, I said that assuming that it was random.. But I guess we might as
well fix it.

> > 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.

Hmm, I just tried mounting something with ganesha and that broke because
it received fid=1730858632 in a TATTACH request, so something in the
patch series made some big fid happens.

If you say this isn't intented though this needs debugging, I'm glad I
brought this up :P

(Note that it really should be fine if it is random within the pool, I
have notified the current developpers of the problem)
-- 
Dominique