NFS: Convert nfs_get_lock_context to return an ERR_PTR on failure

We want to be able to distinguish between allocation failures, and
the case where the lock context is not needed (because there are no
locks).

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/direct.c

@@ -450,16 +450,20 @@ static ssize_t nfs_direct_read(struct kiocb *iocb, const struct iovec *iov,
 	ssize_t result = -ENOMEM;
 	struct inode *inode = iocb->ki_filp->f_mapping->host;
 	struct nfs_direct_req *dreq;
+	struct nfs_lock_context *l_ctx;
 
 	dreq = nfs_direct_req_alloc();
 	if (dreq == NULL)
 		goto out;
 
 	dreq->inode = inode;
 	dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
-	dreq->l_ctx = nfs_get_lock_context(dreq->ctx);
-	if (dreq->l_ctx == NULL)
+	l_ctx = nfs_get_lock_context(dreq->ctx);
+	if (IS_ERR(l_ctx)) {
+		result = PTR_ERR(l_ctx);
 		goto out_release;
+	}
+	dreq->l_ctx = l_ctx;
 	if (!is_sync_kiocb(iocb))
 		dreq->iocb = iocb;
 
@@ -849,16 +853,20 @@ static ssize_t nfs_direct_write(struct kiocb *iocb, const struct iovec *iov,
 	ssize_t result = -ENOMEM;
 	struct inode *inode = iocb->ki_filp->f_mapping->host;
 	struct nfs_direct_req *dreq;
+	struct nfs_lock_context *l_ctx;
 
 	dreq = nfs_direct_req_alloc();
 	if (!dreq)
 		goto out;
 
 	dreq->inode = inode;
 	dreq->ctx = get_nfs_open_context(nfs_file_open_context(iocb->ki_filp));
-	dreq->l_ctx = nfs_get_lock_context(dreq->ctx);
-	if (dreq->l_ctx == NULL)
+	l_ctx = nfs_get_lock_context(dreq->ctx);
+	if (IS_ERR(l_ctx)) {
+		result = PTR_ERR(l_ctx);
 		goto out_release;
+	}
+	dreq->l_ctx = l_ctx;
 	if (!is_sync_kiocb(iocb))
 		dreq->iocb = iocb;
 

fs/nfs/inode.c

@@ -578,7 +578,7 @@ struct nfs_lock_context *nfs_get_lock_context(struct nfs_open_context *ctx)
 		spin_unlock(&inode->i_lock);
 		new = kmalloc(sizeof(*new), GFP_KERNEL);
 		if (new == NULL)
-			return NULL;
+			return ERR_PTR(-ENOMEM);
 		nfs_init_lock_context(new);
 		spin_lock(&inode->i_lock);
 		res = __nfs_find_lock_context(ctx);

fs/nfs/pagelist.c

@@ -102,18 +102,20 @@ nfs_create_request(struct nfs_open_context *ctx, struct inode *inode,
 		   unsigned int offset, unsigned int count)
 {
 	struct nfs_page		*req;
+	struct nfs_lock_context *l_ctx;
 
 	/* try to allocate the request struct */
 	req = nfs_page_alloc();
 	if (req == NULL)
 		return ERR_PTR(-ENOMEM);
 
 	/* get lock context early so we can deal with alloc failures */
-	req->wb_lock_context = nfs_get_lock_context(ctx);
-	if (req->wb_lock_context == NULL) {
+	l_ctx = nfs_get_lock_context(ctx);
+	if (IS_ERR(l_ctx)) {
 		nfs_page_free(req);
-		return ERR_PTR(-ENOMEM);
+		return ERR_CAST(l_ctx);
 	}
+	req->wb_lock_context = l_ctx;
 
 	/* Initialize the request struct. Initially, we assume a
 	 * long write-back delay. This will be adjusted in