nfsd4: Move callback setup to callback queue

Instead of creating the new rpc client from a regular server thread,
set a flag, kick off a null call, and allow the null call to do the work
of setting up the client on the callback workqueue.

Use a spinlock to ensure the callback work gets a consistent view of the
callback parameters.

This allows, for example, changing the callback from contexts where
sleeping is not allowed.  I hope it will also keep the locking simple as
we add more session and trunking features, by serializing most of the
callback-specific work.

This also closes a small race where the the new cb_ident could be used
with an old connection (or vice-versa).
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

fs/nfsd/nfs4callback.c

@@ -284,7 +284,7 @@ nfs4_xdr_enc_cb_recall(struct rpc_rqst *req, __be32 *p,
 	struct xdr_stream xdr;
 	struct nfs4_delegation *args = cb->cb_op;
 	struct nfs4_cb_compound_hdr hdr = {
-		.ident = args->dl_ident,
+		.ident = cb->cb_clp->cl_cb_ident,
 		.minorversion = cb->cb_minorversion,
 	};
 
@@ -506,7 +506,8 @@ int setup_callback_client(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
 			PTR_ERR(client));
 		return PTR_ERR(client);
 	}
-	nfsd4_set_callback_client(clp, client);
+	clp->cl_cb_ident = conn->cb_ident;
+	clp->cl_cb_client = client;
 	return 0;
 
 }
@@ -569,15 +570,12 @@ void do_probe_callback(struct nfs4_client *clp)
  */
 void nfsd4_probe_callback(struct nfs4_client *clp, struct nfs4_cb_conn *conn)
 {
-	int status;
-
 	BUG_ON(atomic_read(&clp->cl_cb_set));
 
-	status = setup_callback_client(clp, conn);
-	if (status) {
-		warn_no_callback_path(clp, status);
-		return;
-	}
+	spin_lock(&clp->cl_lock);
+	memcpy(&clp->cl_cb_conn, conn, sizeof(struct nfs4_cb_conn));
+	set_bit(NFSD4_CLIENT_CB_UPDATE, &clp->cl_cb_flags);
+	spin_unlock(&clp->cl_lock);
 	do_probe_callback(clp);
 }
 
@@ -730,19 +728,16 @@ void nfsd4_destroy_callback_queue(void)
 }
 
 /* must be called under the state lock */
-void nfsd4_set_callback_client(struct nfs4_client *clp, struct rpc_clnt *new)
+void nfsd4_shutdown_callback(struct nfs4_client *clp)
 {
-	struct rpc_clnt *old = clp->cl_cb_client;
-
-	clp->cl_cb_client = new;
+	set_bit(NFSD4_CLIENT_KILL, &clp->cl_cb_flags);
 	/*
-	 * After this, any work that saw the old value of cl_cb_client will
-	 * be gone:
+	 * Note this won't actually result in a null callback;
+	 * instead, nfsd4_do_callback_rpc() will detect the killed
+	 * client, destroy the rpc client, and stop:
 	 */
+	do_probe_callback(clp);
 	flush_workqueue(callback_wq);
-	/* So we can safely shut it down: */
-	if (old)
-		rpc_shutdown_client(old);
 }
 
 void nfsd4_release_cb(struct nfsd4_callback *cb)
@@ -751,15 +746,51 @@ void nfsd4_release_cb(struct nfsd4_callback *cb)
 		cb->cb_ops->rpc_release(cb);
 }
 
+void nfsd4_process_cb_update(struct nfsd4_callback *cb)
+{
+	struct nfs4_cb_conn conn;
+	struct nfs4_client *clp = cb->cb_clp;
+	int err;
+
+	/*
+	 * This is either an update, or the client dying; in either case,
+	 * kill the old client:
+	 */
+	if (clp->cl_cb_client) {
+		rpc_shutdown_client(clp->cl_cb_client);
+		clp->cl_cb_client = NULL;
+	}
+	if (test_bit(NFSD4_CLIENT_KILL, &clp->cl_cb_flags))
+		return;
+	spin_lock(&clp->cl_lock);
+	/*
+	 * Only serialized callback code is allowed to clear these
+	 * flags; main nfsd code can only set them:
+	 */
+	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));
+	spin_unlock(&clp->cl_lock);
+
+	err = setup_callback_client(clp, &conn);
+	if (err)
+		warn_no_callback_path(clp, err);
+}
+
 void nfsd4_do_callback_rpc(struct work_struct *w)
 {
 	struct nfsd4_callback *cb = container_of(w, struct nfsd4_callback, cb_work);
 	struct nfs4_client *clp = cb->cb_clp;
-	struct rpc_clnt *clnt = clp->cl_cb_client;
+	struct rpc_clnt *clnt;
 
-	if (clnt == NULL) {
+	if (clp->cl_cb_flags)
+		nfsd4_process_cb_update(cb);
+
+	clnt = clp->cl_cb_client;
+	if (!clnt) {
+		/* Callback channel broken, or client killed; give up: */
 		nfsd4_release_cb(cb);
-		return; /* Client is shutting down; give up. */
+		return;
 	}
 	rpc_call_async(clnt, &cb->cb_msg, RPC_TASK_SOFT | RPC_TASK_SOFTCONN,
 			cb->cb_ops, cb);

fs/nfsd/nfs4state.c

@@ -207,7 +207,6 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_stateid *stp, struct svc_f
 {
 	struct nfs4_delegation *dp;
 	struct nfs4_file *fp = stp->st_file;
-	struct nfs4_cb_conn *conn = &stp->st_stateowner->so_client->cl_cb_conn;
 
 	dprintk("NFSD alloc_init_deleg\n");
 	/*
@@ -234,7 +233,6 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_stateid *stp, struct svc_f
 	nfs4_file_get_access(fp, O_RDONLY);
 	dp->dl_flock = NULL;
 	dp->dl_type = type;
-	dp->dl_ident = conn->cb_ident;
 	dp->dl_stateid.si_boot = boot_time;
 	dp->dl_stateid.si_stateownerid = current_delegid++;
 	dp->dl_stateid.si_fileid = 0;
@@ -875,7 +873,7 @@ expire_client(struct nfs4_client *clp)
 		sop = list_entry(clp->cl_openowners.next, struct nfs4_stateowner, so_perclient);
 		release_openowner(sop);
 	}
-	nfsd4_set_callback_client(clp, NULL);
+	nfsd4_shutdown_callback(clp);
 	if (clp->cl_cb_conn.cb_xprt)
 		svc_xprt_put(clp->cl_cb_conn.cb_xprt);
 	list_del(&clp->cl_idhash);
@@ -978,6 +976,7 @@ static struct nfs4_client *create_client(struct xdr_netobj name, char *recdir,
 	INIT_LIST_HEAD(&clp->cl_delegations);
 	INIT_LIST_HEAD(&clp->cl_sessions);
 	INIT_LIST_HEAD(&clp->cl_lru);
+	spin_lock_init(&clp->cl_lock);
 	INIT_WORK(&clp->cl_cb_null.cb_work, nfsd4_do_callback_rpc);
 	clp->cl_time = get_seconds();
 	clear_bit(0, &clp->cl_cb_slot_busy);
@@ -1547,7 +1546,7 @@ nfsd4_destroy_session(struct svc_rqst *r,
 
 	nfs4_lock_state();
 	/* wait for callbacks */
-	nfsd4_set_callback_client(ses->se_client, NULL);
+	nfsd4_shutdown_callback(ses->se_client);
 	nfs4_unlock_state();
 	nfsd4_put_session(ses);
 	status = nfs_ok;

fs/nfsd/state.h

@@ -84,7 +84,6 @@ struct nfs4_delegation {
 	u32			dl_type;
 	time_t			dl_time;
 /* For recall: */
-	u32			dl_ident;
 	stateid_t		dl_stateid;
 	struct knfsd_fh		dl_fh;
 	int			dl_retries;
@@ -217,10 +216,17 @@ struct nfs4_client {
 
 	/* for v4.0 and v4.1 callbacks: */
 	struct nfs4_cb_conn	cl_cb_conn;
+#define NFSD4_CLIENT_CB_UPDATE	1
+#define NFSD4_CLIENT_KILL	2
+	unsigned long		cl_cb_flags;
 	struct rpc_clnt		*cl_cb_client;
+	u32			cl_cb_ident;
 	atomic_t		cl_cb_set;
 	struct nfsd4_callback	cl_cb_null;
 
+	/* for all client information that callback code might need: */
+	spinlock_t		cl_lock;
+
 	/* for nfs41 */
 	struct list_head	cl_sessions;
 	struct nfsd4_clid_slot	cl_cs_slot;	/* create_session slot */
@@ -439,7 +445,7 @@ extern void nfsd4_do_callback_rpc(struct work_struct *);
 extern void nfsd4_cb_recall(struct nfs4_delegation *dp);
 extern int nfsd4_create_callback_queue(void);
 extern void nfsd4_destroy_callback_queue(void);
-extern void nfsd4_set_callback_client(struct nfs4_client *, struct rpc_clnt *);
+extern void nfsd4_shutdown_callback(struct nfs4_client *);
 extern void nfs4_put_delegation(struct nfs4_delegation *dp);
 extern __be32 nfs4_make_rec_clidname(char *clidname, struct xdr_netobj *clname);
 extern void nfsd4_init_recdir(char *recdir_name);