NFS: Add an asynchronous delegreturn operation for use in nfs_clear_inode

Otherwise, there is a potential deadlock if the last dput() from an NFSv4
close() or other asynchronous operation leads to nfs_clear_inode calling
the synchronous delegreturn.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/delegation.c

@@ -174,11 +174,11 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
 	return status;
 }
 
-static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation)
+static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation, int issync)
 {
 	int res = 0;
 
-	res = nfs4_proc_delegreturn(inode, delegation->cred, &delegation->stateid);
+	res = nfs4_proc_delegreturn(inode, delegation->cred, &delegation->stateid, issync);
 	nfs_free_delegation(delegation);
 	return res;
 }
@@ -208,7 +208,7 @@ static int __nfs_inode_return_delegation(struct inode *inode, struct nfs_delegat
 	up_read(&clp->cl_sem);
 	nfs_msync_inode(inode);
 
-	return nfs_do_return_delegation(inode, delegation);
+	return nfs_do_return_delegation(inode, delegation, 1);
 }
 
 static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi, const nfs4_stateid *stateid)
@@ -228,6 +228,27 @@ static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfs
 	return NULL;
 }
 
+/*
+ * This function returns the delegation without reclaiming opens
+ * or protecting against delegation reclaims.
+ * It is therefore really only safe to be called from
+ * nfs4_clear_inode()
+ */
+void nfs_inode_return_delegation_noreclaim(struct inode *inode)
+{
+	struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
+	struct nfs_inode *nfsi = NFS_I(inode);
+	struct nfs_delegation *delegation;
+
+	if (rcu_dereference(nfsi->delegation) != NULL) {
+		spin_lock(&clp->cl_lock);
+		delegation = nfs_detach_delegation_locked(nfsi, NULL);
+		spin_unlock(&clp->cl_lock);
+		if (delegation != NULL)
+			nfs_do_return_delegation(inode, delegation, 0);
+	}
+}
+
 int nfs_inode_return_delegation(struct inode *inode)
 {
 	struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
@@ -388,7 +409,7 @@ static int recall_thread(void *data)
 	nfs_msync_inode(inode);
 
 	if (delegation != NULL)
-		nfs_do_return_delegation(inode, delegation);
+		nfs_do_return_delegation(inode, delegation, 1);
 	iput(inode);
 	module_put_and_exit(0);
 }

fs/nfs/delegation.h

@@ -29,6 +29,7 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
 void nfs_inode_reclaim_delegation(struct inode *inode, struct rpc_cred *cred, struct nfs_openres *res);
 int nfs_inode_return_delegation(struct inode *inode);
 int nfs_async_inode_return_delegation(struct inode *inode, const nfs4_stateid *stateid);
+void nfs_inode_return_delegation_noreclaim(struct inode *inode);
 
 struct inode *nfs_delegation_find_inode(struct nfs_client *clp, const struct nfs_fh *fhandle);
 void nfs_return_all_delegations(struct super_block *sb);
@@ -39,7 +40,7 @@ void nfs_delegation_mark_reclaim(struct nfs_client *clp);
 void nfs_delegation_reap_unclaimed(struct nfs_client *clp);
 
 /* NFSv4 delegation-related procedures */
-int nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4_stateid *stateid);
+int nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4_stateid *stateid, int issync);
 int nfs4_open_delegation_recall(struct nfs_open_context *ctx, struct nfs4_state *state, const nfs4_stateid *stateid);
 int nfs4_lock_delegation_recall(struct nfs4_state *state, struct file_lock *fl);
 int nfs4_copy_delegation_stateid(nfs4_stateid *dst, struct inode *inode);

fs/nfs/dir.c

@@ -864,7 +864,6 @@ static int nfs_dentry_delete(struct dentry *dentry)
  */
 static void nfs_dentry_iput(struct dentry *dentry, struct inode *inode)
 {
-	nfs_inode_return_delegation(inode);
 	if (S_ISDIR(inode->i_mode))
 		/* drop any readdir cache as it could easily be old */
 		NFS_I(inode)->cache_validity |= NFS_INO_INVALID_DATA;

fs/nfs/inode.c

@@ -1145,7 +1145,7 @@ static int nfs_update_inode(struct inode *inode, struct nfs_fattr *fattr)
 void nfs4_clear_inode(struct inode *inode)
 {
 	/* If we are holding a delegation, return it! */
-	nfs_inode_return_delegation(inode);
+	nfs_inode_return_delegation_noreclaim(inode);
 	/* First call standard NFS clear_inode() code */
 	nfs_clear_inode(inode);
 }

fs/nfs/nfs4proc.c

@@ -2991,7 +2991,7 @@ static const struct rpc_call_ops nfs4_delegreturn_ops = {
 	.rpc_release = nfs4_delegreturn_release,
 };
 
-static int _nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4_stateid *stateid)
+static int _nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4_stateid *stateid, int issync)
 {
 	struct nfs4_delegreturndata *data;
 	struct nfs_server *server = NFS_SERVER(inode);
@@ -3006,7 +3006,7 @@ static int _nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, co
 		.callback_ops = &nfs4_delegreturn_ops,
 		.flags = RPC_TASK_ASYNC,
 	};
-	int status;
+	int status = 0;
 
 	data = kmalloc(sizeof(*data), GFP_KERNEL);
 	if (data == NULL)
@@ -3028,23 +3028,27 @@ static int _nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, co
 	task = rpc_run_task(&task_setup_data);
 	if (IS_ERR(task))
 		return PTR_ERR(task);
+	if (!issync)
+		goto out;
 	status = nfs4_wait_for_completion_rpc_task(task);
-	if (status == 0) {
+	if (status != 0)
+		goto out;
 	status = data->rpc_status;
-		if (status == 0)
+	if (status != 0)
+		goto out;
 	nfs_refresh_inode(inode, &data->fattr);
-	}
+out:
 	rpc_put_task(task);
 	return status;
 }
 
-int nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4_stateid *stateid)
+int nfs4_proc_delegreturn(struct inode *inode, struct rpc_cred *cred, const nfs4_stateid *stateid, int issync)
 {
 	struct nfs_server *server = NFS_SERVER(inode);
 	struct nfs4_exception exception = { };
 	int err;
 	do {
-		err = _nfs4_proc_delegreturn(inode, cred, stateid);
+		err = _nfs4_proc_delegreturn(inode, cred, stateid, issync);
 		switch (err) {
 			case -NFS4ERR_STALE_STATEID:
 			case -NFS4ERR_EXPIRED: