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

[Chuck Lever]

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

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.


> 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.

-- 
Chuck Lever