[PATCH 2/5] svc: don't hold reference for poolstats, only mutex.

NeilBrown
2023-12-15T01:01:00Z

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@suse.de>
---
fs/nfsd/netns.h | 4 +++-
fs/nfsd/nfsctl.c | 2 +-
fs/nfsd/nfssvc.c | 24 ++----------------------
include/linux/sunrpc/svc.h | 8 +++++++-
net/sunrpc/svc_xprt.c | 32 +++++++++++++++++++++++---------
5 files changed, 36 insertions(+), 34 deletions(-)

diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index ab303a8b77d5..16dbef245dbb 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -123,7 +123,9 @@ struct nfsd_net {
u32 clientid_counter;
u32 clverifier_counter;

- struct svc_serv *nfsd_serv;
+ struct svc_info nfsd_info;
+#define nfsd_serv nfsd_info.serv
+
/* When a listening socket is added to nfsd, keep_active is set
* and this justifies a reference on nfsd_serv. This stops
* nfsd_serv from being freed. When the number of threads is
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 8c84e77a8892..2923da1537d2 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -183,7 +183,7 @@ 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 = seq_release,
};

DEFINE_SHOW_ATTRIBUTE(nfsd_reply_cache_stats);
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 32d06249b3c0..6927edf932e9 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -684,6 +684,7 @@ int nfsd_create_serv(struct net *net)
return error;
}
spin_lock(&nfsd_notifier_lock);
+ nn->nfsd_info.mutex = &nfsd_mutex;
nn->nfsd_serv = serv;
spin_unlock(&nfsd_notifier_lock);

@@ -1083,28 +1084,7 @@ bool nfssvc_encode_voidres(struct svc_rqst *rqstp, struct xdr_stream *xdr)

int nfsd_pool_stats_open(struct inode *inode, struct file *file)
{
- 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) {
- mutex_unlock(&nfsd_mutex);
- return -ENODEV;
- }
- 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)
-{
- 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(&nn->nfsd_info, file);
}
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 544fcfe07479..3bea2840272d 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -97,6 +97,12 @@ struct svc_serv {
#endif /* CONFIG_SUNRPC_BACKCHANNEL */
};

+/* This is used by pool_stats to find and lock an svc */
+struct svc_info {
+ struct svc_serv *serv;
+ struct mutex *mutex;
+};
+
/**
* svc_get() - increment reference count on a SUNRPC serv
* @serv: the svc_serv to have count incremented
@@ -431,7 +437,7 @@ 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_info *si, 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..dbb190606eec 100644
--- a/net/sunrpc/svc_xprt.c
+++ b/net/sunrpc/svc_xprt.c
@@ -1363,29 +1363,36 @@ int svc_xprt_names(struct svc_serv *serv, char *buf, const int buflen)
}
EXPORT_SYMBOL_GPL(svc_xprt_names);

-
/*----------------------------------------------------------------------------*/

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 svc_info *si = m->private;

dprintk("svc_pool_stats_start, *pidx=%u\n", pidx);

+ mutex_lock(si->mutex);
+
if (!pidx)
return SEQ_START_TOKEN;
- return (pidx > serv->sv_nrpools ? NULL : &serv->sv_pools[pidx-1]);
+ if (!si->serv)
+ return NULL;
+ return pidx > si->serv->sv_nrpools ? NULL
+ : &si->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 svc_info *si = m->private;
+ struct svc_serv *serv = si->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 +1407,9 @@ 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 svc_info *si = m->private;
+
+ mutex_unlock(si->mutex);
}

static int svc_pool_stats_show(struct seq_file *m, void *p)
@@ -1427,14 +1437,18 @@ 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_info *info, struct file *file)
{
+ struct seq_file *seq;
int err;

err = seq_open(file, &svc_pool_stats_seq_ops);
- if (!err)
- ((struct seq_file *) file->private_data)->private = serv;
- return err;
+ if (err)
+ return err;
+ seq = file->private_data;
+ seq->private = info;
+
+ return 0;
}
EXPORT_SYMBOL(svc_pool_stats_open);

--
2.43.0