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From:   "NeilBrown" <neilb@suse.de>
To:     "J. Bruce Fields" <bfields@fieldses.org>
Cc:     "Chuck Lever" <chuck.lever@oracle.com>, linux-nfs@vger.kernel.org
Subject: Re: [PATCH 00/14] SUNRPC: clean up server thread management.
In-reply-to: <20211122005901.GB12035@fieldses.org>
References: <163710954700.5485.5622638225352156964.stgit@noble.brown>,
 <20211117141231.GA24762@fieldses.org>,
 <163753863448.13692.4142092237119935826@noble.neil.brown.name>,
 <20211122005639.GA12035@fieldses.org>, <20211122005901.GB12035@fieldses.org>
Date:   Mon, 22 Nov 2021 12:13:08 +1100
Message-id: <163754358887.13692.5665882865660886756@noble.neil.brown.name>
Precedence: bulk

On Mon, 22 Nov 2021, J. Bruce Fields wrote:
> On Sun, Nov 21, 2021 at 07:56:39PM -0500, J. Bruce Fields wrote:
> > On Mon, Nov 22, 2021 at 10:50:34AM +1100, NeilBrown wrote:
> > > On Thu, 18 Nov 2021, J. Bruce Fields wrote:
> > > > On Wed, Nov 17, 2021 at 11:46:49AM +1100, NeilBrown wrote:
> > > > > I have a dream of making nfsd threads start and stop dynamically.
> > > >=20
> > > > It's a good dream!
> > > >=20
> > > > I haven't had a chance to look at these at all yet, I just kicked off
> > > > tests to run overnight, and woke up to the below.
> > > >=20
> > > > This happened on the client, probably the first time it attempted to =
do
> > > > an nfsv4 mount, so something went wrong with setup of the callback
> > > > server.
> > >=20
> > > I cannot reproduce this and cannot see any way it could possible happen.
> >=20
> > Huh.  Well, it's possible I mixed up the results somehow.  I'll see if I
> > can reproduce tonight or tomorrow.
> >=20
> > > Could you please confirm the patches were applied on a vanilla 5.1.6-rc1
> > > kernel, and that you don't have the "pool_mode" module parameter set.
> >=20
> > /sys/module/sunrpc/parameters/pool_mode is "global", the default.
>=20
> Oh, and yes, this is what I was testing, should just be 5.16-rc1 plus
> your 14 patches:
>=20
> 	http://git.linux-nfs.org/?p=3Dbfields/linux-topics.git;a=3Dshortlog;h=3D65=
9e13af1f8702776704676937932f332265d85e

Thanks!

I did find a possible problem.  Very first patch.
in fs/nfsd/nfsctl.c, in _write_ports_addfd()
  if (!err && !nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))

should be "err >=3D 0" rather than "!err".  That could result in a
use-after free, which can make anything explode.
If not too much trouble, could you just tweek that line and see what
happens?

Thanks,
NeilBrown