[PATCH 4/5] SUNRPC: discard sv_refcnt, and svc_get/svc_put

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

sv_refcnt is no longer useful.
lockd and nfs-cb only ever have the svc active when there are a non-zero
number of threads, so sv_refcnt mirrors sv_nrthreads.

nfsd also keeps the svc active between when a socket is added and when
the first thread is started, but we don't really need a refcount for
that. We can simply not destroy the svc while there are any permanent
sockets attached.

So remove sv_refcnt and the get/put functions.
Instead of a final call to svc_put(), call svc_destroy() instead.
This is changed to also store NULL in the passed-in pointer to make it
easier to avoid use-after-free situations.

Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/lockd/svc.c | 10 ++++------
fs/nfs/callback.c | 13 ++++++-------
fs/nfsd/netns.h | 7 -------
fs/nfsd/nfsctl.c | 15 ++++-----------
fs/nfsd/nfsd.h | 7 -------
fs/nfsd/nfssvc.c | 26 ++++----------------------
include/linux/sunrpc/svc.h | 27 +--------------------------
net/sunrpc/svc.c | 13 ++++---------
8 files changed, 23 insertions(+), 95 deletions(-)

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 81be07c1d3d1..0d6cb3fdc0e1 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -345,10 +345,10 @@ static int lockd_get(void)

serv->sv_maxconn = nlm_max_connections;
error = svc_set_num_threads(serv, NULL, 1);
- /* The thread now holds the only reference */
- svc_put(serv);
- if (error < 0)
+ if (error < 0) {
+ svc_destroy(&serv);
return error;
+ }

nlmsvc_serv = serv;
register_inetaddr_notifier(&lockd_inetaddr_notifier);
@@ -372,11 +372,9 @@ static void lockd_put(void)
unregister_inet6addr_notifier(&lockd_inet6addr_notifier);
#endif

- svc_get(nlmsvc_serv);
svc_set_num_threads(nlmsvc_serv, NULL, 0);
- svc_put(nlmsvc_serv);
timer_delete_sync(&nlmsvc_retry);
- nlmsvc_serv = NULL;
+ svc_destroy(&nlmsvc_serv);
dprintk("lockd_down: service destroyed\n");
}

diff --git a/fs/nfs/callback.c b/fs/nfs/callback.c
index 4ffa1f469e90..760d27dd7225 100644
--- a/fs/nfs/callback.c
+++ b/fs/nfs/callback.c
@@ -187,7 +187,7 @@ static struct svc_serv *nfs_callback_create_svc(int minorversion)
* Check whether we're already up and running.
*/
if (cb_info->serv)
- return svc_get(cb_info->serv);
+ return cb_info->serv;

/*
* Sanity check: if there's no task,
@@ -245,9 +245,10 @@ int nfs_callback_up(u32 minorversion, struct rpc_xprt *xprt)

cb_info->users++;
err_net:
- if (!cb_info->users)
- cb_info->serv = NULL;
- svc_put(serv);
+ if (!cb_info->users) {
+ svc_set_num_threads(cb_info->serv, NULL, 0);
+ svc_destroy(&cb_info->serv);
+ }
err_create:
mutex_unlock(&nfs_callback_mutex);
return ret;
@@ -271,11 +272,9 @@ void nfs_callback_down(int minorversion, struct net *net)
nfs_callback_down_net(minorversion, serv, net);
cb_info->users--;
if (cb_info->users == 0) {
- svc_get(serv);
svc_set_num_threads(serv, NULL, 0);
- svc_put(serv);
dprintk("nfs_callback_down: service destroyed\n");
- cb_info->serv = NULL;
+ svc_destroy(&cb_info->serv);
}
mutex_unlock(&nfs_callback_mutex);
}
diff --git a/fs/nfsd/netns.h b/fs/nfsd/netns.h
index 16dbef245dbb..74b4360779a1 100644
--- a/fs/nfsd/netns.h
+++ b/fs/nfsd/netns.h
@@ -126,13 +126,6 @@ struct nfsd_net {
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
- * set, keep_active is cleared and the reference is dropped. So
- * when the last thread exits, the service will be destroyed.
- */
- int keep_active;

/*
* clientid and stateid data for construction of net unique COPY
diff --git a/fs/nfsd/nfsctl.c b/fs/nfsd/nfsctl.c
index 3368eb5342dc..d0089cc5dc4c 100644
--- a/fs/nfsd/nfsctl.c
+++ b/fs/nfsd/nfsctl.c
@@ -709,13 +709,10 @@ static ssize_t __write_ports_addfd(char *buf, struct net *net, const struct cred

err = svc_addsock(nn->nfsd_serv, net, fd, buf, SIMPLE_TRANSACTION_LIMIT, cred);

- if (err < 0 && !nn->nfsd_serv->sv_nrthreads && !nn->keep_active)
+ if (!nn->nfsd_serv->sv_nrthreads &&
+ list_empty(&nn->nfsd_serv->sv_permsocks))
nfsd_last_thread(net);
- else if (err >= 0 &&
- !nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
- svc_get(nn->nfsd_serv);

- nfsd_put(net);
return err;
}

@@ -751,10 +748,6 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
if (err < 0 && err != -EAFNOSUPPORT)
goto out_close;

- if (!nn->nfsd_serv->sv_nrthreads && !xchg(&nn->keep_active, 1))
- svc_get(nn->nfsd_serv);
-
- nfsd_put(net);
return 0;
out_close:
xprt = svc_find_xprt(nn->nfsd_serv, transport, net, PF_INET, port);
@@ -763,10 +756,10 @@ static ssize_t __write_ports_addxprt(char *buf, struct net *net, const struct cr
svc_xprt_put(xprt);
}
out_err:
- if (!nn->nfsd_serv->sv_nrthreads && !nn->keep_active)
+ if (!nn->nfsd_serv->sv_nrthreads &&
+ list_empty(&nn->nfsd_serv->sv_permsocks))
nfsd_last_thread(net);

- nfsd_put(net);
return err;
}

diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index 3286ffacbc56..9ed0e08d16c2 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -113,13 +113,6 @@ int nfsd_pool_stats_open(struct inode *, struct file *);
int nfsd_pool_stats_release(struct inode *, struct file *);
void nfsd_shutdown_threads(struct net *net);

-static inline void nfsd_put(struct net *net)
-{
- struct nfsd_net *nn = net_generic(net, nfsd_net_id);
-
- svc_put(nn->nfsd_serv);
-}
-
bool i_am_nfsd(void);

struct nfsdfs_client {
diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c
index 6927edf932e9..d670adfbc15b 100644
--- a/fs/nfsd/nfssvc.c
+++ b/fs/nfsd/nfssvc.c
@@ -59,15 +59,6 @@ static __be32 nfsd_init_request(struct svc_rqst *,
* nfsd_mutex protects nn->nfsd_serv -- both the pointer itself and some members
* of the svc_serv struct such as ->sv_temp_socks and ->sv_permsocks.
*
- * If (out side the lock) nn->nfsd_serv is non-NULL, then it must point to a
- * properly initialised 'struct svc_serv' with ->sv_nrthreads > 0 (unless
- * nn->keep_active is set). That number of nfsd threads must
- * exist and each must be listed in ->sp_all_threads in some entry of
- * ->sv_pools[].
- *
- * Each active thread holds a counted reference on nn->nfsd_serv, as does
- * the nn->keep_active flag and various transient calls to svc_get().
- *
* Finally, the nfsd_mutex also protects some of the global variables that are
* accessed when nfsd starts and that are settable via the write_* routines in
* nfsctl.c. In particular:
@@ -572,6 +563,7 @@ void nfsd_last_thread(struct net *net)

nfsd_shutdown_net(net);
nfsd_export_flush(net);
+ svc_destroy(&serv);
}

void nfsd_reset_versions(struct nfsd_net *nn)
@@ -646,11 +638,9 @@ void nfsd_shutdown_threads(struct net *net)
return;
}

- svc_get(serv);
/* Kill outstanding nfsd threads */
svc_set_num_threads(serv, NULL, 0);
nfsd_last_thread(net);
- svc_put(serv);
mutex_unlock(&nfsd_mutex);
}

@@ -666,10 +656,9 @@ int nfsd_create_serv(struct net *net)
struct svc_serv *serv;

WARN_ON(!mutex_is_locked(&nfsd_mutex));
- if (nn->nfsd_serv) {
- svc_get(nn->nfsd_serv);
+ if (nn->nfsd_serv)
return 0;
- }
+
if (nfsd_max_blksize == 0)
nfsd_max_blksize = nfsd_get_default_max_blksize();
nfsd_reset_versions(nn);
@@ -680,7 +669,7 @@ int nfsd_create_serv(struct net *net)
serv->sv_maxconn = nn->max_connections;
error = svc_bind(serv, net);
if (error < 0) {
- svc_put(serv);
+ svc_destroy(&serv);
return error;
}
spin_lock(&nfsd_notifier_lock);
@@ -764,7 +753,6 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
nthreads[0] = 1;

/* apply the new numbers */
- svc_get(nn->nfsd_serv);
for (i = 0; i < n; i++) {
err = svc_set_num_threads(nn->nfsd_serv,
&nn->nfsd_serv->sv_pools[i],
@@ -772,7 +760,6 @@ int nfsd_set_nrthreads(int n, int *nthreads, struct net *net)
if (err)
break;
}
- svc_put(nn->nfsd_serv);
return err;
}

@@ -814,13 +801,8 @@ nfsd_svc(int nrservs, struct net *net, const struct cred *cred)
goto out_put;
error = serv->sv_nrthreads;
out_put:
- /* Threads now hold service active */
- if (xchg(&nn->keep_active, 0))
- svc_put(serv);
-
if (serv->sv_nrthreads == 0)
nfsd_last_thread(net);
- svc_put(serv);
out:
mutex_unlock(&nfsd_mutex);
return error;
diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index 3bea2840272d..8d7888234e9e 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -69,7 +69,6 @@ struct svc_serv {
struct svc_program * sv_program; /* RPC program */
struct svc_stat * sv_stats; /* RPC statistics */
spinlock_t sv_lock;
- struct kref sv_refcnt;
unsigned int sv_nrthreads; /* # of server threads */
unsigned int sv_maxconn; /* max connections allowed or
* '0' causing max to be based
@@ -103,31 +102,7 @@ struct svc_info {
struct mutex *mutex;
};

-/**
- * svc_get() - increment reference count on a SUNRPC serv
- * @serv: the svc_serv to have count incremented
- *
- * Returns: the svc_serv that was passed in.
- */
-static inline struct svc_serv *svc_get(struct svc_serv *serv)
-{
- kref_get(&serv->sv_refcnt);
- return serv;
-}
-
-void svc_destroy(struct kref *);
-
-/**
- * svc_put - decrement reference count on a SUNRPC serv
- * @serv: the svc_serv to have count decremented
- *
- * When the reference count reaches zero, svc_destroy()
- * is called to clean up and free the serv.
- */
-static inline void svc_put(struct svc_serv *serv)
-{
- kref_put(&serv->sv_refcnt, svc_destroy);
-}
+void svc_destroy(struct svc_serv **svcp);

/*
* Maximum payload size supported by a kernel RPC server.
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index fa4e23fa0e09..eb5856e1351d 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -463,7 +463,6 @@ __svc_create(struct svc_program *prog, unsigned int bufsize, int npools,
return NULL;
serv->sv_name = prog->pg_name;
serv->sv_program = prog;
- kref_init(&serv->sv_refcnt);
serv->sv_stats = prog->pg_stats;
if (bufsize > RPCSVC_MAXPAYLOAD)
bufsize = RPCSVC_MAXPAYLOAD;
@@ -564,11 +563,13 @@ EXPORT_SYMBOL_GPL(svc_create_pooled);
* protect sv_permsocks and sv_tempsocks.
*/
void
-svc_destroy(struct kref *ref)
+svc_destroy(struct svc_serv **servp)
{
- struct svc_serv *serv = container_of(ref, struct svc_serv, sv_refcnt);
+ struct svc_serv *serv = *servp;
unsigned int i;

+ *servp = NULL;
+
dprintk("svc: svc_destroy(%s)\n", serv->sv_program->pg_name);
timer_shutdown_sync(&serv->sv_temptimer);

@@ -675,7 +676,6 @@ svc_prepare_thread(struct svc_serv *serv, struct svc_pool *pool, int node)
if (!rqstp)
return ERR_PTR(-ENOMEM);

- svc_get(serv);
spin_lock_bh(&serv->sv_lock);
serv->sv_nrthreads += 1;
spin_unlock_bh(&serv->sv_lock);
@@ -935,11 +935,6 @@ svc_exit_thread(struct svc_rqst *rqstp)

svc_rqst_free(rqstp);

- svc_put(serv);
- /* That svc_put() cannot be the last, because the thread
- * waiting for SP_VICTIM_REMAINS to clear must hold
- * a reference. So it is still safe to access pool.
- */
clear_and_wake_up_bit(SP_VICTIM_REMAINS, &pool->sp_flags);
}
EXPORT_SYMBOL_GPL(svc_exit_thread);
--
2.43.0