nfsd4: allow backchannel recovery

Now that we have a list of connections to choose from, we can teach the
callback code to just pick a suitable connection and use that, instead
of insisting on forever using the connection that the first
create_session was sent with.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

2 files changed, 43 insertions, 9 deletions

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index dd183af24fe6..18b740bd29ac 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -473,8 +473,7 @@ static int max_cb_time(void)
 /* Reference counting, callback cleanup, etc., all look racy as heck.
  * And why is cl_cb_set an atomic? */
 
-static int setup_callback_client(struct nfs4_client *clp,
-                struct nfs4_cb_conn *conn)
+static int setup_callback_client(struct nfs4_client *clp, struct nfs4_cb_conn *conn, struct nfsd4_session *ses)
 {
         struct rpc_timeout      timeparms = {
                 .to_initval     = max_cb_time(),
@@ -501,6 +500,10 @@ static int setup_callback_client(struct nfs4_client *clp,
                 args.protocol = XPRT_TRANSPORT_TCP;
                 clp->cl_cb_ident = conn->cb_ident;
         } else {
+                if (!conn->cb_xprt)
+                        return -EINVAL;
+                clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
+                clp->cl_cb_session = ses;
                 args.bc_xprt = conn->cb_xprt;
                 args.prognumber = clp->cl_cb_session->se_cb_prog;
                 args.protocol = XPRT_TRANSPORT_BC_TCP;
@@ -756,10 +759,27 @@ static void nfsd4_release_cb(struct nfsd4_callback *cb)
                 cb->cb_ops->rpc_release(cb);
 }
 
+/* requires cl_lock: */
+static struct nfsd4_conn * __nfsd4_find_backchannel(struct nfs4_client *clp)
+{
+        struct nfsd4_session *s;
+        struct nfsd4_conn *c;
+
+        list_for_each_entry(s, &clp->cl_sessions, se_perclnt) {
+                list_for_each_entry(c, &s->se_conns, cn_persession) {
+                        if (c->cn_flags & NFS4_CDFC4_BACK)
+                                return c;
+                }
+        }
+        return NULL;
+}
+
 static void nfsd4_process_cb_update(struct nfsd4_callback *cb)
 {
         struct nfs4_cb_conn conn;
         struct nfs4_client *clp = cb->cb_clp;
+        struct nfsd4_session *ses = NULL;
+        struct nfsd4_conn *c;
         int err;
 
         /*
@@ -770,6 +790,10 @@ static void nfsd4_process_cb_update(struct nfsd4_callback *cb)
                 rpc_shutdown_client(clp->cl_cb_client);
                 clp->cl_cb_client = NULL;
         }
+        if (clp->cl_cb_conn.cb_xprt) {
+                svc_xprt_put(clp->cl_cb_conn.cb_xprt);
+                clp->cl_cb_conn.cb_xprt = NULL;
+        }
         if (test_bit(NFSD4_CLIENT_KILL, &clp->cl_cb_flags))
                 return;
         spin_lock(&clp->cl_lock);
@@ -780,9 +804,15 @@ static void nfsd4_process_cb_update(struct nfsd4_callback *cb)
         BUG_ON(!clp->cl_cb_flags);
         clear_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_cb_flags);
         memcpy(&conn, &cb->cb_clp->cl_cb_conn, sizeof(struct nfs4_cb_conn));
+        c = __nfsd4_find_backchannel(clp);
+        if (c) {
+                svc_xprt_get(c->cn_xprt);
+                conn.cb_xprt = c->cn_xprt;
+                ses = c->cn_session;
+        }
         spin_unlock(&clp->cl_lock);
 
-        err = setup_callback_client(clp, &conn);
+        err = setup_callback_client(clp, &conn, ses);
         if (err)
                 warn_no_callback_path(clp, err);
 }
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 956174f488a7..290370bc9ae7 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -642,6 +642,7 @@ static void nfsd4_conn_lost(struct svc_xpt_user *u)
                 free_conn(c);
         }
         spin_unlock(&clp->cl_lock);
+        /* XXX: mark callback for update, probe callback */
 }
 
 static struct nfsd4_conn *alloc_conn(struct svc_rqst *rqstp, u32 flags)
@@ -790,16 +791,19 @@ static struct nfsd4_session *alloc_init_session(struct svc_rqst *rqstp, struct n
                 free_session(&new->se_ref);
                 return NULL;
         }
-        if (!clp->cl_cb_session && (cses->flags & SESSION4_BACK_CHAN)) {
+        if (cses->flags & SESSION4_BACK_CHAN) {
                 struct sockaddr *sa = svc_addr(rqstp);
-
-                clp->cl_cb_session = new;
-                clp->cl_cb_conn.cb_xprt = rqstp->rq_xprt;
-                svc_xprt_get(rqstp->rq_xprt);
+                /*
+                 * This is a little silly; with sessions there's no real
+                 * use for the callback address.  Use the peer address
+                 * as a reasonable default for now, but consider fixing
+                 * the rpc client not to require an address in the
+                 * future:
+                 */
                 rpc_copy_addr((struct sockaddr *)&clp->cl_cb_conn.cb_addr, sa);
                 clp->cl_cb_conn.cb_addrlen = svc_addr_len(sa);
-                nfsd4_probe_callback(clp);
         }
+        nfsd4_probe_callback(clp);
         return new;
 }