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

On 12 Jun 2025, at 12:42, Chuck Lever wrote:

On 6/12/25 12:15 PM, Jeff Layton wrote:

quoted

On Thu, 2025-06-12 at 12:05 -0400, Chuck Lever wrote:

quoted

On 6/12/25 11:57 AM, Jeff Layton wrote:

quoted

On Tue, 2025-05-27 at 20:12 -0400, Jeff Layton wrote:

quoted

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/ (local)
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.

RHEL 10 is shiny and new, and Fedora is bleeding edge. It's not likely
either of these are deployed in production environments yet. Just sayin
that in this case, the Bayesian filter leans towards waiting a full dev
cycle.

We don't consider it acceptable to allow known defects to persist in our
products just because they are bleeding edge.

quoted

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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.

If someone can confirm that it is effective, I'll add it to nfsd-fixes.

I'm sure it is if Jeff spent time on it.

We're going to try to get this into RHEL-10 ASAP, because dropped RPCs
manifest as datacenter-wide problems that are very hard to diagnose.  Its a
real pain that we won't have an upstream commit assigned for it.

Ben