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.
> + 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>
