NFSv4: Fix delegation return in cases where we have to retry

If we're unable to immediately recover all locks because the server is
unable to immediately service our reclaim calls, then we want to retry
after we've finished servicing all the other asynchronous delegation
returns on our queue.
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/delegation.c

@@ -75,6 +75,13 @@ void nfs_mark_delegation_referenced(struct nfs_delegation *delegation)
 	set_bit(NFS_DELEGATION_REFERENCED, &delegation->flags);
 }
 
+static void nfs_mark_return_delegation(struct nfs_server *server,
+				       struct nfs_delegation *delegation)
+{
+	set_bit(NFS_DELEGATION_RETURN, &delegation->flags);
+	set_bit(NFS4CLNT_DELEGRETURN, &server->nfs_client->cl_state);
+}
+
 static bool
 nfs4_is_valid_delegation(const struct nfs_delegation *delegation,
 		fmode_t flags)
@@ -293,6 +300,7 @@ nfs_start_delegation_return_locked(struct nfs_inode *nfsi)
 		goto out;
 	spin_lock(&delegation->lock);
 	if (!test_and_set_bit(NFS_DELEGATION_RETURNING, &delegation->flags)) {
+		clear_bit(NFS_DELEGATION_RETURN_DELAYED, &delegation->flags);
 		/* Refcount matched in nfs_end_delegation_return() */
 		ret = nfs_get_delegation(delegation);
 	}
@@ -314,16 +322,17 @@ nfs_start_delegation_return(struct nfs_inode *nfsi)
 	return delegation;
 }
 
-static void
-nfs_abort_delegation_return(struct nfs_delegation *delegation,
-		struct nfs_client *clp)
+static void nfs_abort_delegation_return(struct nfs_delegation *delegation,
+					struct nfs_client *clp, int err)
 {
 
 	spin_lock(&delegation->lock);
 	clear_bit(NFS_DELEGATION_RETURNING, &delegation->flags);
-	set_bit(NFS_DELEGATION_RETURN, &delegation->flags);
+	if (err == -EAGAIN) {
+		set_bit(NFS_DELEGATION_RETURN_DELAYED, &delegation->flags);
+		set_bit(NFS4CLNT_DELEGRETURN_DELAYED, &clp->cl_state);
+	}
 	spin_unlock(&delegation->lock);
-	set_bit(NFS4CLNT_DELEGRETURN, &clp->cl_state);
 }
 
 static struct nfs_delegation *
@@ -539,7 +548,7 @@ static int nfs_end_delegation_return(struct inode *inode, struct nfs_delegation
 	} while (err == 0);
 
 	if (err) {
-		nfs_abort_delegation_return(delegation, clp);
+		nfs_abort_delegation_return(delegation, clp, err);
 		goto out;
 	}
 
@@ -568,6 +577,7 @@ static bool nfs_delegation_need_return(struct nfs_delegation *delegation)
 	if (ret)
 		clear_bit(NFS_DELEGATION_RETURN_IF_CLOSED, &delegation->flags);
 	if (test_bit(NFS_DELEGATION_RETURNING, &delegation->flags) ||
+	    test_bit(NFS_DELEGATION_RETURN_DELAYED, &delegation->flags) ||
 	    test_bit(NFS_DELEGATION_REVOKED, &delegation->flags))
 		ret = false;
 
@@ -647,6 +657,38 @@ static int nfs_server_return_marked_delegations(struct nfs_server *server,
 	return err;
 }
 
+static bool nfs_server_clear_delayed_delegations(struct nfs_server *server)
+{
+	struct nfs_delegation *d;
+	bool ret = false;
+
+	list_for_each_entry_rcu (d, &server->delegations, super_list) {
+		if (!test_bit(NFS_DELEGATION_RETURN_DELAYED, &d->flags))
+			continue;
+		nfs_mark_return_delegation(server, d);
+		clear_bit(NFS_DELEGATION_RETURN_DELAYED, &d->flags);
+		ret = true;
+	}
+	return ret;
+}
+
+static bool nfs_client_clear_delayed_delegations(struct nfs_client *clp)
+{
+	struct nfs_server *server;
+	bool ret = false;
+
+	if (!test_and_clear_bit(NFS4CLNT_DELEGRETURN_DELAYED, &clp->cl_state))
+		goto out;
+	rcu_read_lock();
+	list_for_each_entry_rcu (server, &clp->cl_superblocks, client_link) {
+		if (nfs_server_clear_delayed_delegations(server))
+			ret = true;
+	}
+	rcu_read_unlock();
+out:
+	return ret;
+}
+
 /**
  * nfs_client_return_marked_delegations - return previously marked delegations
  * @clp: nfs_client to process
@@ -659,8 +701,14 @@ static int nfs_server_return_marked_delegations(struct nfs_server *server,
  */
 int nfs_client_return_marked_delegations(struct nfs_client *clp)
 {
-	return nfs_client_for_each_server(clp,
-			nfs_server_return_marked_delegations, NULL);
+	int err = nfs_client_for_each_server(
+		clp, nfs_server_return_marked_delegations, NULL);
+	if (err)
+		return err;
+	/* If a return was delayed, sleep to prevent hard looping */
+	if (nfs_client_clear_delayed_delegations(clp))
+		ssleep(1);
+	return 0;
 }
 
 /**
@@ -775,13 +823,6 @@ static void nfs_mark_return_if_closed_delegation(struct nfs_server *server,
 	set_bit(NFS4CLNT_DELEGRETURN, &server->nfs_client->cl_state);
 }
 
-static void nfs_mark_return_delegation(struct nfs_server *server,
-		struct nfs_delegation *delegation)
-{
-	set_bit(NFS_DELEGATION_RETURN, &delegation->flags);
-	set_bit(NFS4CLNT_DELEGRETURN, &server->nfs_client->cl_state);
-}
-
 static bool nfs_server_mark_return_all_delegations(struct nfs_server *server)
 {
 	struct nfs_delegation *delegation;

fs/nfs/delegation.h

@@ -36,6 +36,7 @@ enum {
 	NFS_DELEGATION_REVOKED,
 	NFS_DELEGATION_TEST_EXPIRED,
 	NFS_DELEGATION_INODE_FREEING,
+	NFS_DELEGATION_RETURN_DELAYED,
 };
 
 int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,

fs/nfs/nfs4_fs.h

@@ -45,6 +45,7 @@ enum nfs4_client_state {
 	NFS4CLNT_RECALL_RUNNING,
 	NFS4CLNT_RECALL_ANY_LAYOUT_READ,
 	NFS4CLNT_RECALL_ANY_LAYOUT_RW,
+	NFS4CLNT_DELEGRETURN_DELAYED,
 };
 
 #define NFS4_RENEW_TIMEOUT		0x01