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

Ben Hutchings
2018-10-14T23:16:19Z

From: Eryu Guan <guaneryu@gmail.com>

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@suse.cz>
Suggested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.16: The relevant code is in ext4_ind_direct_IO()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- 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'