nfs_localio: simplify interface to nfsd for getting nfsd_file

The nfsd_localio_operations structure contains nfsd_file_get() to get a
reference to an nfsd_file.  This is only used in one place, where
nfsd_open_local_fh() is also used.

This patch combines the two, calling nfsd_open_local_fh() passing a
pointer to where the nfsd_file pointer might be stored.  If there is a
pointer there an nfsd_file_get() can get a reference, that reference is
returned.  If not a new nfsd_file is acquired, stored at the pointer,
and returned.  When we store a reference we also increase the refcount
on the net, as that refcount is decrements when we clear the stored
pointer.

We now get an extra reference *before* storing the new nfsd_file at the
given location.  This avoids possible races with the nfsd_file being
freed before the final reference can be taken.

This patch moves the rcu_dereference() needed after fetching from
ro_file or rw_file into the nfsd code where the 'struct nfs_file' is
fully defined.  This avoids an error reported by older versions of gcc
such as gcc-8 which complain about rcu_dereference() use in contexts
where the structure (which will supposedly be accessed) is not fully
defined.

Reported-by: Pali Rohár <pali@kernel.org>
Reported-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Fixes: 86e00412254a ("nfs: cache all open LOCALIO nfsd_file(s) in client")
Signed-off-by: NeilBrown <neil@brown.name>
Signed-off-by: Anna Schumaker <anna.schumaker@oracle.com>

diff --git a/fs/nfs/localio.c b/fs/nfs/localio.c
index 86df8d2cd22e83ecd4b9d418c4297c652e16e45c..ef12dd279539a5ad1e0f3a918cd93ada7d99ff75 100644 (file)
--- a/fs/nfs/localio.c
+++ b/fs/nfs/localio.c
@@ -209,11 +209,6 @@ void nfs_local_probe_async(struct nfs_client *clp)
 }
 EXPORT_SYMBOL_GPL(nfs_local_probe_async);
 
-static inline struct nfsd_file *nfs_local_file_get(struct nfsd_file *nf)
-{
-       return nfs_to->nfsd_file_get_local(nf);
-}
-
 static inline void nfs_local_file_put(struct nfsd_file *nf)
 {
        nfs_to_nfsd_file_put_local(nf);
@@ -228,12 +223,13 @@ static inline void nfs_local_file_put(struct nfsd_file *nf)
 static struct nfsd_file *
 __nfs_local_open_fh(struct nfs_client *clp, const struct cred *cred,
                    struct nfs_fh *fh, struct nfs_file_localio *nfl,
+                   struct nfsd_file __rcu **pnf,
                    const fmode_t mode)
 {
        struct nfsd_file *localio;
 
        localio = nfs_open_local_fh(&clp->cl_uuid, clp->cl_rpcclient,
-                                   cred, fh, nfl, mode);
+                                   cred, fh, nfl, pnf, mode);
        if (IS_ERR(localio)) {
                int status = PTR_ERR(localio);
                trace_nfs_local_open_fh(fh, mode, status);
@@ -260,7 +256,7 @@ nfs_local_open_fh(struct nfs_client *clp, const struct cred *cred,
                  struct nfs_fh *fh, struct nfs_file_localio *nfl,
                  const fmode_t mode)
 {
-       struct nfsd_file *nf, *new, __rcu **pnf;
+       struct nfsd_file *nf, __rcu **pnf;
 
        if (!nfs_server_is_local(clp))
                return NULL;
@@ -272,24 +268,9 @@ nfs_local_open_fh(struct nfs_client *clp, const struct cred *cred,
        else
                pnf = &nfl->ro_file;
 
-       new = NULL;
-       rcu_read_lock();
-       nf = rcu_dereference(*pnf);
-       if (!nf) {
-               rcu_read_unlock();
-               new = __nfs_local_open_fh(clp, cred, fh, nfl, mode);
-               if (IS_ERR(new))
-                       return NULL;
-               rcu_read_lock();
-               /* try to swap in the pointer */
-               nf = unrcu_pointer(cmpxchg(pnf, NULL, RCU_INITIALIZER(new)));
-               if (!nf)
-                       swap(nf, new);
-       }
-       nf = nfs_local_file_get(nf);
-       rcu_read_unlock();
-       if (new)
-               nfs_to_nfsd_file_put_local(new);
+       nf = __nfs_local_open_fh(clp, cred, fh, nfl, pnf, mode);
+       if (IS_ERR(nf))
+               return NULL;
        return nf;
 }
 EXPORT_SYMBOL_GPL(nfs_local_open_fh);

diff --git a/fs/nfs_common/nfslocalio.c b/fs/nfs_common/nfslocalio.c
index f6821b2c87a2f1e170bc3127279ffb83baf69a15..503f85f64b7609ca49788142b8519a48d018dffd 100644 (file)
--- a/fs/nfs_common/nfslocalio.c
+++ b/fs/nfs_common/nfslocalio.c
@@ -237,6 +237,7 @@ static void nfs_uuid_add_file(nfs_uuid_t *nfs_uuid, struct nfs_file_localio *nfl
 struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *uuid,
                   struct rpc_clnt *rpc_clnt, const struct cred *cred,
                   const struct nfs_fh *nfs_fh, struct nfs_file_localio *nfl,
+                  struct nfsd_file __rcu **pnf,
                   const fmode_t fmode)
 {
        struct net *net;
@@ -261,7 +262,7 @@ struct nfsd_file *nfs_open_local_fh(nfs_uuid_t *uuid,
        rcu_read_unlock();
        /* We have an implied reference to net thanks to nfsd_net_try_get */
        localio = nfs_to->nfsd_open_local_fh(net, uuid->dom, rpc_clnt,
-                                            cred, nfs_fh, fmode);
+                                            cred, nfs_fh, pnf, fmode);
        nfs_to_nfsd_net_put(net);
        if (!IS_ERR(localio))
                nfs_uuid_add_file(uuid, nfl);

diff --git a/fs/nfsd/localio.c b/fs/nfsd/localio.c
index 2c0afd1067ea61c200272ab7f74298a472a87f55..80d9ff6608a7b99ebcfbc9e437d0261ec07c3157 100644 (file)
--- a/fs/nfsd/localio.c
+++ b/fs/nfsd/localio.c
@@ -24,20 +24,6 @@
 #include "filecache.h"
 #include "cache.h"
 
-static const struct nfsd_localio_operations nfsd_localio_ops = {
-       .nfsd_net_try_get  = nfsd_net_try_get,
-       .nfsd_net_put  = nfsd_net_put,
-       .nfsd_open_local_fh = nfsd_open_local_fh,
-       .nfsd_file_put_local = nfsd_file_put_local,
-       .nfsd_file_get_local = nfsd_file_get_local,
-       .nfsd_file_file = nfsd_file_file,
-};
-
-void nfsd_localio_ops_init(void)
-{
-       nfs_to = &nfsd_localio_ops;
-}
-
 /**
  * nfsd_open_local_fh - lookup a local filehandle @nfs_fh and map to nfsd_file
  *
@@ -46,6 +32,7 @@ void nfsd_localio_ops_init(void)
  * @rpc_clnt: rpc_clnt that the client established
  * @cred: cred that the client established
  * @nfs_fh: filehandle to lookup
+ * @nfp: place to find the nfsd_file, or store it if it was non-NULL
  * @fmode: fmode_t to use for open
  *
  * This function maps a local fh to a path on a local filesystem.
@@ -56,10 +43,11 @@ void nfsd_localio_ops_init(void)
  * set. Caller (NFS client) is responsible for calling nfsd_net_put and
  * nfsd_file_put (via nfs_to_nfsd_file_put_local).
  */
-struct nfsd_file *
+static struct nfsd_file *
 nfsd_open_local_fh(struct net *net, struct auth_domain *dom,
                   struct rpc_clnt *rpc_clnt, const struct cred *cred,
-                  const struct nfs_fh *nfs_fh, const fmode_t fmode)
+                  const struct nfs_fh *nfs_fh, struct nfsd_file __rcu **pnf,
+                  const fmode_t fmode)
 {
        int mayflags = NFSD_MAY_LOCALIO;
        struct svc_cred rq_cred;
@@ -73,6 +61,12 @@ nfsd_open_local_fh(struct net *net, struct auth_domain *dom,
        if (!nfsd_net_try_get(net))
                return ERR_PTR(-ENXIO);
 
+       rcu_read_lock();
+       localio = nfsd_file_get(rcu_dereference(*pnf));
+       rcu_read_unlock();
+       if (localio)
+               return localio;
+
        /* nfs_fh -> svc_fh */
        fh_init(&fh, NFS4_FHSIZE);
        fh.fh_handle.fh_size = nfs_fh->size;
@@ -94,12 +88,47 @@ nfsd_open_local_fh(struct net *net, struct auth_domain *dom,
        if (rq_cred.cr_group_info)
                put_group_info(rq_cred.cr_group_info);
 
-       if (IS_ERR(localio))
+       if (!IS_ERR(localio)) {
+               struct nfsd_file *new;
+               if (!nfsd_net_try_get(net)) {
+                       nfsd_file_put(localio);
+                       nfsd_net_put(net);
+                       return ERR_PTR(-ENXIO);
+               }
+               nfsd_file_get(localio);
+       again:
+               new = unrcu_pointer(cmpxchg(pnf, NULL, RCU_INITIALIZER(localio)));
+               if (new) {
+                       /* Some other thread installed an nfsd_file */
+                       if (nfsd_file_get(new) == NULL)
+                               goto again;
+                       /*
+                        * Drop the ref we were going to install and the
+                        * one we were going to return.
+                        */
+                       nfsd_file_put(localio);
+                       nfsd_file_put(localio);
+                       localio = new;
+               }
+       } else
                nfsd_net_put(net);
 
        return localio;
 }
-EXPORT_SYMBOL_GPL(nfsd_open_local_fh);
+
+static const struct nfsd_localio_operations nfsd_localio_ops = {
+       .nfsd_net_try_get  = nfsd_net_try_get,
+       .nfsd_net_put  = nfsd_net_put,
+       .nfsd_open_local_fh = nfsd_open_local_fh,
+       .nfsd_file_put_local = nfsd_file_put_local,
+       .nfsd_file_get_local = nfsd_file_get_local,
+       .nfsd_file_file = nfsd_file_file,
+};
+
+void nfsd_localio_ops_init(void)
+{
+       nfs_to = &nfsd_localio_ops;
+}
 
 /*
  * UUID_IS_LOCAL XDR functions