ext4: add i_data_sem sanity check

Each caller of ext4_ext_dirty must hold i_data_sem,
The only exception is migration code, let's make it convenient.
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

fs/ext4/extents.c

@@ -161,6 +161,8 @@ int __ext4_ext_dirty(const char *where, unsigned int line, handle_t *handle,
 		     struct inode *inode, struct ext4_ext_path *path)
 {
 	int err;
+
+	WARN_ON(!rwsem_is_locked(&EXT4_I(inode)->i_data_sem));
 	if (path->p_bh) {
 		ext4_extent_block_csum_set(inode, ext_block_hdr(path->p_bh));
 		/* path points to block */

fs/ext4/migrate.c

@@ -39,6 +39,8 @@ static int finish_range(handle_t *handle, struct inode *inode,
 	newext.ee_block = cpu_to_le32(lb->first_block);
 	newext.ee_len   = cpu_to_le16(lb->last_block - lb->first_block + 1);
 	ext4_ext_store_pblock(&newext, lb->first_pblock);
+	/* Locking only for convinience since we are operating on temp inode */
+	down_write(&EXT4_I(inode)->i_data_sem);
 	path = ext4_ext_find_extent(inode, lb->first_block, NULL, 0);
 
 	if (IS_ERR(path)) {
@@ -61,7 +63,9 @@ static int finish_range(handle_t *handle, struct inode *inode,
 	 */
 	if (needed && ext4_handle_has_enough_credits(handle,
 						EXT4_RESERVE_TRANS_BLOCKS)) {
+		up_write((&EXT4_I(inode)->i_data_sem));
 		retval = ext4_journal_restart(handle, needed);
+		down_write((&EXT4_I(inode)->i_data_sem));
 		if (retval)
 			goto err_out;
 	} else if (needed) {
@@ -70,13 +74,16 @@ static int finish_range(handle_t *handle, struct inode *inode,
 			/*
 			 * IF not able to extend the journal restart the journal
 			 */
+			up_write((&EXT4_I(inode)->i_data_sem));
 			retval = ext4_journal_restart(handle, needed);
+			down_write((&EXT4_I(inode)->i_data_sem));
 			if (retval)
 				goto err_out;
 		}
 	}
 	retval = ext4_ext_insert_extent(handle, inode, path, &newext, 0);
 err_out:
+	up_write((&EXT4_I(inode)->i_data_sem));
 	if (path) {
 		ext4_ext_drop_refs(path);
 		kfree(path);