ext4: remove i_mutex from ext4_file_sync()

After removal of ext4_flush_unwritten_io() call, ext4_file_sync()
doesn't need i_mutex anymore. Forcing of transaction commits doesn't
need i_mutex as there's nothing inode specific in that code apart from
grabbing transaction ids from the inode. So remove the lock.
Reviewed-by: NZheng Liu <wenqing.lz@taobao.com>
Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>

fs/ext4/fsync.c

@@ -99,20 +99,18 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 	trace_ext4_sync_file_enter(file, datasync);
 
 	if (inode->i_sb->s_flags & MS_RDONLY)
-		goto out_trace;
+		goto out;
 
 	if (!journal) {
 		ret = generic_file_fsync(file, start, end, datasync);
 		if (!ret && !hlist_empty(&inode->i_dentry))
 			ret = ext4_sync_parent(inode);
-		goto out_trace;
+		goto out;
 	}
 
 	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	if (ret)
 		return ret;
-	mutex_lock(&inode->i_mutex);
-
 	/*
 	 * data=writeback,ordered:
 	 *  The caller's filemap_fdatawrite()/wait will sync the data.
@@ -143,8 +141,6 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 			ret = err;
 	}
 out:
-	mutex_unlock(&inode->i_mutex);
-out_trace:
 	trace_ext4_sync_file_exit(inode, ret);
 	return ret;
 }