ext4: fix lost truncate due to race with writeback
The following race can lead to a loss of i_disksize update from truncate
thus resulting in a wrong inode size if the inode size isn't updated
again before inode is reclaimed:
ext4_setattr() mpage_map_and_submit_extent()
EXT4_I(inode)->i_disksize = attr->ia_size;
... ...
disksize = ((loff_t)mpd->first_page) << PAGE_CACHE_SHIFT
/* False because i_size isn't
* updated yet */
if (disksize > i_size_read(inode))
/* True, because i_disksize is
* already truncated */
if (disksize > EXT4_I(inode)->i_disksize)
/* Overwrite i_disksize
* update from truncate */
ext4_update_i_disksize()
i_size_write(inode, attr->ia_size);
For other places updating i_disksize such race cannot happen because
i_mutex prevents these races. Writeback is the only place where we do
not hold i_mutex and we cannot grab it there because of lock ordering.
We fix the race by doing both i_disksize and i_size update in truncate
atomically under i_data_sem and in mpage_map_and_submit_extent() we move
the check against i_size under i_data_sem as well.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: stable@vger.kernel.org
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 38f4301..fc4051e 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2237,12 +2237,10 @@
/* Update on-disk size after IO is submitted */
disksize = ((loff_t)mpd->first_page) << PAGE_CACHE_SHIFT;
- if (disksize > i_size_read(inode))
- disksize = i_size_read(inode);
if (disksize > EXT4_I(inode)->i_disksize) {
int err2;
- ext4_update_i_disksize(inode, disksize);
+ ext4_wb_update_i_disksize(inode, disksize);
err2 = ext4_mark_inode_dirty(handle, inode);
if (err2)
ext4_error(inode->i_sb,
@@ -4627,18 +4625,27 @@
error = ext4_orphan_add(handle, inode);
orphan = 1;
}
+ down_write(&EXT4_I(inode)->i_data_sem);
EXT4_I(inode)->i_disksize = attr->ia_size;
rc = ext4_mark_inode_dirty(handle, inode);
if (!error)
error = rc;
+ /*
+ * We have to update i_size under i_data_sem together
+ * with i_disksize to avoid races with writeback code
+ * running ext4_wb_update_i_disksize().
+ */
+ if (!error)
+ i_size_write(inode, attr->ia_size);
+ up_write(&EXT4_I(inode)->i_data_sem);
ext4_journal_stop(handle);
if (error) {
ext4_orphan_del(NULL, inode);
goto err_out;
}
- }
+ } else
+ i_size_write(inode, attr->ia_size);
- i_size_write(inode, attr->ia_size);
/*
* Blocks are going to be removed from the inode. Wait
* for dio in flight. Temporarily disable