nfsd4: fix 4.1 connection registration race

If a connection is closed just after a sequence or create_session
is sent over it, we could end up trying to register a callback that will
never get called since the xprt is already marked dead.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

2 files changed, 26 insertions, 8 deletions

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index f1e5ec6b510..ad2bfa68d53 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -673,16 +673,17 @@ static void nfsd4_hash_conn(struct nfsd4_conn *conn, struct nfsd4_session *ses)
         spin_unlock(&clp->cl_lock);
 }
 
-static void nfsd4_register_conn(struct nfsd4_conn *conn)
+static int nfsd4_register_conn(struct nfsd4_conn *conn)
 {
         conn->cn_xpt_user.callback = nfsd4_conn_lost;
-        register_xpt_user(conn->cn_xprt, &conn->cn_xpt_user);
+        return register_xpt_user(conn->cn_xprt, &conn->cn_xpt_user);
 }
 
 static __be32 nfsd4_new_conn(struct svc_rqst *rqstp, struct nfsd4_session *ses)
 {
         struct nfsd4_conn *conn;
         u32 flags = NFS4_CDFC4_FORE;
+        int ret;
 
         if (ses->se_flags & SESSION4_BACK_CHAN)
                 flags |= NFS4_CDFC4_BACK;
@@ -690,7 +691,10 @@ static __be32 nfsd4_new_conn(struct svc_rqst *rqstp, struct nfsd4_session *ses)
         if (!conn)
                 return nfserr_jukebox;
         nfsd4_hash_conn(conn, ses);
-        nfsd4_register_conn(conn);
+        ret = nfsd4_register_conn(conn);
+        if (ret)
+                /* oops; xprt is already down: */
+                nfsd4_conn_lost(&conn->cn_xpt_user);
         return nfs_ok;
 }
 
@@ -1644,6 +1648,7 @@ static void nfsd4_sequence_check_conn(struct nfsd4_conn *new, struct nfsd4_sessi
 {
         struct nfs4_client *clp = ses->se_client;
         struct nfsd4_conn *c;
+        int ret;
 
         spin_lock(&clp->cl_lock);
         c = __nfsd4_find_conn(new->cn_xprt, ses);
@@ -1654,7 +1659,10 @@ static void nfsd4_sequence_check_conn(struct nfsd4_conn *new, struct nfsd4_sessi
         }
         __nfsd4_hash_conn(new, ses);
         spin_unlock(&clp->cl_lock);
-        nfsd4_register_conn(new);
+        ret = nfsd4_register_conn(new);
+        if (ret)
+                /* oops; xprt is already down: */
+                nfsd4_conn_lost(&new->cn_xpt_user);
         return;
 }
 
diff --git a/include/linux/sunrpc/svc_xprt.h b/include/linux/sunrpc/svc_xprt.h
index bbdb680ffbe..aea0d438e3c 100644
--- a/include/linux/sunrpc/svc_xprt.h
+++ b/include/linux/sunrpc/svc_xprt.h
@@ -82,18 +82,28 @@ struct svc_xprt {
         struct net              *xpt_net;
 };
 
-static inline void register_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
+static inline void unregister_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
 {
         spin_lock(&xpt->xpt_lock);
-        list_add(&u->list, &xpt->xpt_users);
+        list_del_init(&u->list);
         spin_unlock(&xpt->xpt_lock);
 }
 
-static inline void unregister_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
+static inline int register_xpt_user(struct svc_xprt *xpt, struct svc_xpt_user *u)
 {
         spin_lock(&xpt->xpt_lock);
-        list_del_init(&u->list);
+        if (test_bit(XPT_CLOSE, &xpt->xpt_flags)) {
+                /*
+                 * The connection is about to be deleted soon (or,
+                 * worse, may already be deleted--in which case we've
+                 * already notified the xpt_users).
+                 */
+                spin_unlock(&xpt->xpt_lock);
+                return -ENOTCONN;
+        }
+        list_add(&u->list, &xpt->xpt_users);
         spin_unlock(&xpt->xpt_lock);
+        return 0;
 }
 
 int     svc_reg_xprt_class(struct svc_xprt_class *);