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

[Lorenzo Bianconi <lorenzo@kernel.org>]

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> 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.

yep, the idea was to avoid grabbing the mutex and dump the refcount instead but
I think it is fine.

Regards,
Lorenzo

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

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