Re: [PATCH 1/2] nfsd: use threads array as-is in netlink interface

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2025-06-12 at 12:05 -0400, Chuck Lever wrote:
> On 6/12/25 11:57 AM, Jeff Layton wrote:
> > On Tue, 2025-05-27 at 20:12 -0400, Jeff Layton wrote:
> > > The old nfsdfs interface for starting a server with multiple pools
> > > handles the special case of a single entry array passed down from
> > > userland by distributing the threads over every NUMA node.
> > > 
> > > The netlink control interface however constructs an array of length
> > > nfsd_nrpools() and fills any unprovided slots with 0's. This behavior
> > > defeats the special casing that the old interface relies on.
> > > 
> > > Change nfsd_nl_threads_set_doit() to pass down the array from userland
> > > as-is.
> > > 
> > > Fixes: 7f5c330b2620 ("nfsd: allow passing in array of thread counts via netlink")
> > > Reported-by: Mike Snitzer <snitzer@kernel.org>
> > > Closes: https://lore.kernel.org/linux-nfs/aDC-ftnzhJAlwqwh@kernel.org/
> > > Signed-off-by: Jeff Layton <jlayton@kernel.org>
> > > ---
> > >  fs/nfsd/nfsctl.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > > index ac265d6fde35df4e02b955050f5b0ef22e6e519c..22101e08c3e80350668e94c395058bc228b08e64 100644
> > > --- a/fs/nfsd/nfsctl.c
> > > +++ b/fs/nfsd/nfsctl.c
> > > @@ -1611,7 +1611,7 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
> > >   */
> > >  int nfsd_nl_threads_set_doit(struct sk_buff *skb, struct genl_info *info)
> > >  {
> > > -	int *nthreads, count = 0, nrpools, i, ret = -EOPNOTSUPP, rem;
> > > +	int *nthreads, nrpools = 0, i, ret = -EOPNOTSUPP, rem;
> > >  	struct net *net = genl_info_net(info);
> > >  	struct nfsd_net *nn = net_generic(net, nfsd_net_id);
> > >  	const struct nlattr *attr;
> > > @@ -1623,12 +1623,11 @@ int nfsd_nl_threads_set_doit(struct sk_buff *skb, struct genl_info *info)
> > >  	/* count number of SERVER_THREADS values */
> > >  	nlmsg_for_each_attr(attr, info->nlhdr, GENL_HDRLEN, rem) {
> > >  		if (nla_type(attr) == NFSD_A_SERVER_THREADS)
> > > -			count++;
> > > +			nrpools++;
> > >  	}
> > >  
> > >  	mutex_lock(&nfsd_mutex);
> > >  
> > > -	nrpools = max(count, nfsd_nrpools(net));
> > >  	nthreads = kcalloc(nrpools, sizeof(int), GFP_KERNEL);
> > >  	if (!nthreads) {
> > >  		ret = -ENOMEM;
> > 
> > I noticed that this didn't go in to the recent merge window.
> > 
> > This patch fixes a rather nasty regression when you try to start the
> > server on a NUMA-capable box.
> 
> The NFSD netlink interface is not broadly used yet, is it?
> 

It is. RHEL10 shipped with it, for instance and it's been in Fedora for
a while.

> Since this one came in late during the 6.16 dev cycle and the Fixes: tag
> references a commit that is already in released kernels, I put in the
> "next merge window" pile. On it's own it doesn't look urgent to me.
> 

I'd really like to see this go in soon and to stable. If you want me to
respin the changelog, I can. It's not a crash, but it manifests as lost
RPCs that just hang. It took me quite a while to figure out what was
going on, and I'd prefer that we not put users through that.

> 
> > It all looks like it works, but some RPCs
> > get silently dropped on the floor (if they happen to be received into a
> > node with no threads). It took me a while to track down the problem
> > after Mike reported it.
> > 
> > Can we go ahead and pull this in and send it to stable?
> > 
> > Also, did this patch fix the problem for you, Mike?
> 
> I'll wait for confirmation.

-- 
Jeff Layton <jlayton@kernel.org>