NFS: Don't inadvertently clear writeback errors

vfs_fsync() has the side effect of clearing unreported writeback errors,
so we need to make sure that we do not abuse it in situations where
applications might not normally expect us to report those errors.

The solution is to replace calls to vfs_fsync() with calls to nfs_wb_all().
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/file.c

@@ -147,7 +147,7 @@ nfs_file_flush(struct file *file, fl_owner_t id)
 		return 0;
 
 	/* Flush writes to the server and return any errors */
-	return vfs_fsync(file, 0);
+	return nfs_wb_all(inode);
 }
 
 ssize_t
@@ -655,7 +655,7 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
 
 	/* Return error values */
 	if (nfs_need_check_write(file, inode)) {
-		int err = vfs_fsync(file, 0);
+		int err = nfs_wb_all(inode);
 		if (err < 0)
 			result = err;
 	}
@@ -709,7 +709,7 @@ do_unlk(struct file *filp, int cmd, struct file_lock *fl, int is_local)
 	 * Flush all pending writes before doing anything
 	 * with locks..
 	 */
-	vfs_fsync(filp, 0);
+	nfs_wb_all(inode);
 
 	l_ctx = nfs_get_lock_context(nfs_file_open_context(filp));
 	if (!IS_ERR(l_ctx)) {

fs/nfs/nfs4file.c

@@ -125,7 +125,7 @@ nfs4_file_flush(struct file *file, fl_owner_t id)
 		return filemap_fdatawrite(file->f_mapping);
 
 	/* Flush writes to the server and return any errors */
-	return vfs_fsync(file, 0);
+	return nfs_wb_all(inode);
 }
 
 #ifdef CONFIG_NFS_V4_2