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

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Jun 12, 2025 at 11:57:59AM -0400, 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. 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?

Hi Jeff,

I saw your other mail asking the same, figured it best to reply to this
thread with the patch.

YES, I just verified this patch fixes the issue I reported.  I didn't
think I was critical path for confirming the fix, and since I had
worked around it (by downgrading nfs-utils from EL10's 2.8.2 to EL9's
2.5.4 it wasn't a super quick thing for me to test.. it became
out-of-sight-out-of-mind...

BTW, Chuck, I think the reason there aren't many/any reports (even
with RHEL10 or Fedora users) is that the user needs to:
1) have a NUMA system
2) explicitly change sunrpc's default for pool_mode from global to pernode.

Anyway:

Tested-by: Mike Snitzer <snitzer@kernel.org>