[PATCH 3.16 045/366] ext4: protect i_disksize update by i_data_sem in direct write path

[Ben Hutchings]

3.16.60-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Eryu Guan <guaneryu@xxxxxxxxx>

commit 73fdad00b208b139cf43f3163fbc0f67e4c6047c upstream.

i_disksize update should be protected by i_data_sem, by either taking
the lock explicitly or by using ext4_update_i_disksize() helper. But the
i_disksize updates in ext4_direct_IO_write() are not protected at all,
which may be racing with i_disksize updates in writeback path in
delalloc buffer write path.

This is found by code inspection, and I didn't hit any i_disksize
corruption due to this bug. Thanks to Jan Kara for catching this bug and
suggesting the fix!

Reported-by: Jan Kara <jack@xxxxxxx>
Suggested-by: Jan Kara <jack@xxxxxxx>
Signed-off-by: Eryu Guan <guaneryu@xxxxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
[bwh: Backported to 3.16: The relevant code is in ext4_ind_direct_IO()]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -649,7 +649,6 @@ ssize_t ext4_ind_direct_IO(int rw, struc
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file->f_mapping->host;
-	struct ext4_inode_info *ei = EXT4_I(inode);
 	handle_t *handle;
 	ssize_t ret;
 	int orphan = 0;
@@ -672,7 +671,7 @@ ssize_t ext4_ind_direct_IO(int rw, struc
 				goto out;
 			}
 			orphan = 1;
-			ei->i_disksize = inode->i_size;
+			ext4_update_i_disksize(inode, inode->i_size);
 			ext4_journal_stop(handle);
 		}
 	}
@@ -731,7 +730,7 @@ locked:
 		if (ret > 0) {
 			loff_t end = offset + ret;
 			if (end > inode->i_size) {
-				ei->i_disksize = end;
+				ext4_update_i_disksize(inode, end);
 				i_size_write(inode, end);
 				/*
 				 * We're going to return a positive `ret'