On Tue, 31 Oct 2023, Jeff Layton wrote:
> On Mon, 2023-10-30 at 12:08 +1100, NeilBrown wrote:
> > A future patch will remove refcounting on svc_serv as it is of little
> > use.
> > It is currently used to keep the svc around while the pool_stats file is
> > open.
> > Change this to get the pointer, protected by the mutex, only in
> > seq_start, and the release the mutex in seq_stop.
> > This means that if the nfsd server is stopped and restarted while the
> > pool_stats file it open, then some pool stats info could be from the
> > first instance and some from the second. This might appear odd, but is
> > unlikely to be a problem in practice.
> >
> > Signed-off-by: NeilBrown <neilb@xxxxxxx>
> > ---
> > fs/nfsd/nfsctl.c | 2 +-
> > fs/nfsd/nfssvc.c | 30 ++++++++---------------
> > include/linux/sunrpc/svc.h | 5 +++-
> > net/sunrpc/svc_xprt.c | 49 ++++++++++++++++++++++++++++++++------
> > 4 files changed, 57 insertions(+), 29 deletions(-)
> >
> > diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
> > index 79efb1075f38..d78ae4452946 100644
> > --- a/fs/nfsd/nfsctl.c
> > +++ b/fs/nfsd/nfsctl.c
> > @@ -179,7 +179,7 @@ static const struct file_operations pool_stats_operations = {
> > .open = nfsd_pool_stats_open,
> > .read = seq_read,
> > .llseek = seq_lseek,
> > - .release = nfsd_pool_stats_release,
> > + .release = svc_pool_stats_release,
> > };
> >
> > DEFINE_SHOW_ATTRIBUTE(nfsd_reply_cache_stats);
> > diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
> > index 6c968c02cc29..203e1cfc1cad 100644
> > --- a/fs/nfsd/nfssvc.c
> > +++ b/fs/nfsd/nfssvc.c
> > @@ -1072,30 +1072,20 @@ bool nfssvc_encode_voidres(struct svc_rqst *rqstp, struct xdr_stream *xdr)
> > return true;
> > }
> >
> > -int nfsd_pool_stats_open(struct inode *inode, struct file *file)
> > +static struct svc_serv *nfsd_get_serv(struct seq_file *s, bool start)
> > {
> > - int ret;
> > - struct nfsd_net *nn = net_generic(inode->i_sb->s_fs_info, nfsd_net_id);
> > -
> > - mutex_lock(&nfsd_mutex);
> > - if (nn->nfsd_serv == NULL) {
> > + struct nfsd_net *nn = net_generic(file_inode(s->file)->i_sb->s_fs_info,
> > + nfsd_net_id);
> > + if (start) {
> > + mutex_lock(&nfsd_mutex);
> > + return nn->nfsd_serv;
> > + } else {
> > mutex_unlock(&nfsd_mutex);
> > - return -ENODEV;
> > + return NULL;
> > }
> > - svc_get(nn->nfsd_serv);
> > - ret = svc_pool_stats_open(nn->nfsd_serv, file);
> > - mutex_unlock(&nfsd_mutex);
> > - return ret;
> > }
> >
> > -int nfsd_pool_stats_release(struct inode *inode, struct file *file)
> > +int nfsd_pool_stats_open(struct inode *inode, struct file *file)
> > {
> > - struct seq_file *seq = file->private_data;
> > - struct svc_serv *serv = seq->private;
> > - int ret = seq_release(inode, file);
> > -
> > - mutex_lock(&nfsd_mutex);
> > - svc_put(serv);
> > - mutex_unlock(&nfsd_mutex);
> > - return ret;
> > + return svc_pool_stats_open(nfsd_get_serv, file);
> > }
> > diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
> > index b10f987509cc..11acad6988a2 100644
> > --- a/include/linux/sunrpc/svc.h
> > +++ b/include/linux/sunrpc/svc.h
> > @@ -433,7 +433,10 @@ void svc_exit_thread(struct svc_rqst *);
> > struct svc_serv * svc_create_pooled(struct svc_program *, unsigned int,
> > int (*threadfn)(void *data));
> > int svc_set_num_threads(struct svc_serv *, struct svc_pool *, int);
> > -int svc_pool_stats_open(struct svc_serv *serv, struct file *file);
> > +int svc_pool_stats_open(struct svc_serv *(*get_serv)(struct seq_file *, bool),
> > + struct file *file);
> > +int svc_pool_stats_release(struct inode *inode,
> > + struct file *file);
> > void svc_process(struct svc_rqst *rqstp);
> > void svc_process_bc(struct rpc_rqst *req, struct svc_rqst *rqstp);
> > int svc_register(const struct svc_serv *, struct net *, const int,
> > diff --git a/net/sunrpc/svc_xprt.c b/net/sunrpc/svc_xprt.c
> > index fee83d1024bc..2f99f7475b7b 100644
> > --- a/net/sunrpc/svc_xprt.c
> > +++ b/net/sunrpc/svc_xprt.c
> > @@ -1366,26 +1366,38 @@ EXPORT_SYMBOL_GPL(svc_xprt_names);
> >
> > /*----------------------------------------------------------------------------*/
> >
> > +struct pool_private {
> > + struct svc_serv *(*get_serv)(struct seq_file *, bool);
>
> This bool is pretty ugly. I think I'd rather see two operations here
> (get_serv/put_serv). Also, this could use a kerneldoc comment.
I agree that bool is ugly, but two function pointers as function args
seemed ugly, and stashing them in 'struct svc_serv' seemed ugly.
So I picked one. I'd be keen to find an approach that didn't require a
function pointer.
Maybe sunrpc could declare
struct svc_ref {
struct mutex mutex;
struct svc_serv *serv;
}
and nfsd could use one of those instead of nfsd_mutex and nfsd_serv, and
pass a pointer to it to the open function.
But then the mutex would have to be in the per-net structure. And maybe
that isn't a bad idea, but it is a change...
I guess I could pass pointers to nfsd_mutex and nn->nfsd_serv to the
open function....
Any other ideas?
Thanks,
NeilBrown
>
> > + struct svc_serv *serv;
> > +};
> > +
> > static void *svc_pool_stats_start(struct seq_file *m, loff_t *pos)
> > {
> > unsigned int pidx = (unsigned int)*pos;
> > - struct svc_serv *serv = m->private;
> > + struct pool_private *pp = m->private;
> >
> > dprintk("svc_pool_stats_start, *pidx=%u\n", pidx);
> >
> > + pp->serv = pp->get_serv(m, true);
> > +
> > if (!pidx)
> > return SEQ_START_TOKEN;
> > - return (pidx > serv->sv_nrpools ? NULL : &serv->sv_pools[pidx-1]);
> > + if (!pp->serv)
> > + return NULL;
> > + return (pidx > pp->serv->sv_nrpools ? NULL : &pp->serv->sv_pools[pidx-1]);
> > }
> >
> > static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
> > {
> > struct svc_pool *pool = p;
> > - struct svc_serv *serv = m->private;
> > + struct pool_private *pp = m->private;
> > + struct svc_serv *serv = pp->serv;
> >
> > dprintk("svc_pool_stats_next, *pos=%llu\n", *pos);
> >
> > - if (p == SEQ_START_TOKEN) {
> > + if (!serv) {
> > + pool = NULL;
> > + } else if (p == SEQ_START_TOKEN) {
> > pool = &serv->sv_pools[0];
> > } else {
> > unsigned int pidx = (pool - &serv->sv_pools[0]);
> > @@ -1400,6 +1412,9 @@ static void *svc_pool_stats_next(struct seq_file *m, void *p, loff_t *pos)
> >
> > static void svc_pool_stats_stop(struct seq_file *m, void *p)
> > {
> > + struct pool_private *pp = m->private;
> > +
> > + pp->get_serv(m, false);
> > }
> >
> > static int svc_pool_stats_show(struct seq_file *m, void *p)
> > @@ -1427,15 +1442,35 @@ static const struct seq_operations svc_pool_stats_seq_ops = {
> > .show = svc_pool_stats_show,
> > };
> >
> > -int svc_pool_stats_open(struct svc_serv *serv, struct file *file)
> > +int svc_pool_stats_open(struct svc_serv *(*get_serv)(struct seq_file *, bool),
> > + struct file *file)
> > {
> > + struct pool_private *pp;
> > int err;
> >
> > + pp = kmalloc(sizeof(*pp), GFP_KERNEL);
> > + if (!pp)
> > + return -ENOMEM;
> > +
> > err = seq_open(file, &svc_pool_stats_seq_ops);
> > - if (!err)
> > - ((struct seq_file *) file->private_data)->private = serv;
> > + if (!err) {
> > + pp->get_serv = get_serv;
> > + ((struct seq_file *) file->private_data)->private = pp;
> > + } else
> > + kfree(pp);
> > +
> > return err;
> > }
> > EXPORT_SYMBOL(svc_pool_stats_open);
> >
> > +int svc_pool_stats_release(struct inode *inode, struct file *file)
> > +{
> > + struct seq_file *seq = file->private_data;
> > +
> > + kfree(seq->private);
> > + seq->private = NULL;
> > + return seq_release(inode, file);
> > +}
> > +EXPORT_SYMBOL(svc_pool_stats_release);
> > +
> > /*----------------------------------------------------------------------------*/
>
> --
> Jeff Layton <jlayton@xxxxxxxxxx>
>
