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

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Message-ID: <a8d4c4cffe1a35ea831110ce1c7beea649352238.camel@kernel.org>
Date: Thu, 12 Jun 2025 11:57:59 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Chuck Lever <chuck.lever@...cle.com>, Neil Brown <neilb@...e.de>, Olga
 Kornievskaia <okorniev@...hat.com>, Dai Ngo <Dai.Ngo@...cle.com>, Tom
 Talpey <tom@...pey.com>, Steven Rostedt	 <rostedt@...dmis.org>, Masami
 Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Trond Myklebust <trondmy@...nel.org>,
 Anna Schumaker	 <anna@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet	 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni	 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>
Cc: Mike Snitzer <snitzer@...nel.org>, linux-nfs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] nfsd: use threads array as-is in netlink interface

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@...nel.org>
> Closes: https://lore.kernel.org/linux-nfs/aDC-ftnzhJAlwqwh@kernel.org/
> Signed-off-by: Jeff Layton <jlayton@...nel.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?

Thanks,
-- 
Jeff Layton <jlayton@...nel.org>