Re: [PATCH 3/5] nfsd: hold nfsd_mutex across entire netlink operation

[Jeff Layton <jlayton@kernel.org>]

On Mon, 2023-10-30 at 12:08 +1100, NeilBrown wrote:
> Rather than using svc_get() and svc_put() to hold a stable reference to
> the nfsd_svc for netlink lookups, simply hold the mutex for the entire
> time.
> 
> The "entire" time isn't very long, and the mutex is not often contented.
> 
> This makes way for use to remove the refcounts of svc, which is more
> confusing than useful.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
>  fs/nfsd/nfsctl.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> index d78ae4452946..8f644f1d157c 100644
> --- a/fs/nfsd/nfsctl.c
> +++ b/fs/nfsd/nfsctl.c
> @@ -1515,11 +1515,10 @@ int nfsd_nl_rpc_status_get_start(struct netlink_callback *cb)
>  	int ret = -ENODEV;
>  
>  	mutex_lock(&nfsd_mutex);
> -	if (nn->nfsd_serv) {
> -		svc_get(nn->nfsd_serv);
> +	if (nn->nfsd_serv)
>  		ret = 0;
> -	}
> -	mutex_unlock(&nfsd_mutex);
> +	else
> +		mutex_unlock(&nfsd_mutex);
>  
>  	return ret;
>  }
> @@ -1691,8 +1690,6 @@ int nfsd_nl_rpc_status_get_dumpit(struct sk_buff *skb,
>   */
>  int nfsd_nl_rpc_status_get_done(struct netlink_callback *cb)
>  {
> -	mutex_lock(&nfsd_mutex);
> -	nfsd_put(sock_net(cb->skb->sk));
>  	mutex_unlock(&nfsd_mutex);
>  
>  	return 0;

(cc'ing Lorenzo since he wrote this)

I think Lorenzo did it this way originally, and I convinced him to take
a reference instead. This should be fine though.

Reviewed-by: Jeff Layton <jlayton@kernel.org>