fs/9p: Use truncate_setsize instead of vmtruncate

convert vmtruncate usage to truncate_setsize. We also writeback
all dirty pages before doing 9p operations and on success call truncate_setsize.
This ensure that we continue sanely on failed truncate on the server. The
disadvantage is that we are now going to write back the content that get
thrown away later as a part of truncate.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/fs/9p/vfs_inode_dotl.c b/fs/9p/vfs_inode_dotl.c
index 327c578..0a0ac30 100644
--- a/fs/9p/vfs_inode_dotl.c
+++ b/fs/9p/vfs_inode_dotl.c
@@ -456,12 +456,6 @@
 	if (IS_ERR(fid))
 		return PTR_ERR(fid);
 
-	if ((iattr->ia_valid & ATTR_SIZE) &&
-	    iattr->ia_size != i_size_read(dentry->d_inode)) {
-		retval = vmtruncate(dentry->d_inode, iattr->ia_size);
-		if (retval)
-			return retval;
-	}
 	/* Write all dirty data */
 	if (S_ISREG(dentry->d_inode->i_mode))
 		filemap_write_and_wait(dentry->d_inode->i_mapping);
@@ -469,8 +463,12 @@
 	retval = p9_client_setattr(fid, &p9attr);
 	if (retval < 0)
 		return retval;
-	v9fs_invalidate_inode_attr(dentry->d_inode);
 
+	if ((iattr->ia_valid & ATTR_SIZE) &&
+	    iattr->ia_size != i_size_read(dentry->d_inode))
+		truncate_setsize(dentry->d_inode, iattr->ia_size);
+
+	v9fs_invalidate_inode_attr(dentry->d_inode);
 	setattr_copy(dentry->d_inode, iattr);
 	mark_inode_dirty(dentry->d_inode);
 	if (iattr->ia_valid & ATTR_MODE) {