Hi Dave,
On 2023/10/12 08:26, Dave Chinner wrote:
On Wed, Oct 11, 2023 at 04:21:55PM +0200, Jan Kara wrote:
Gao Xiang has reported that on ext4 O_SYNC direct IO does not properly
sync file size update and thus if we crash at unfortunate moment, the
file can have smaller size although O_SYNC IO has reported successful
completion. The problem happens because update of on-disk inode size is
handled in ext4_dio_write_iter() *after* iomap_dio_rw() (and thus
dio_complete() in particular) has returned and generic_file_sync() gets
called by dio_complete(). Fix the problem by handling on-disk inode size
update directly in our ->end_io completion handler.
References: https://lore.kernel.org/all/02d18236-26ef-09b0-90ad-030c4fe3ee20@xxxxxxxxxxxxxxxxx
Reported-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
fs/ext4/file.c | 139 ++++++++++++++++++-------------------------------
1 file changed, 52 insertions(+), 87 deletions(-)
.....
@@ -388,9 +342,28 @@ static ssize_t ext4_handle_inode_extension(struct inode *inode, loff_t offset,
*/
if (inode->i_nlink)
ext4_orphan_del(NULL, inode);
+ return;
}
+ /*
+ * If i_disksize got extended due to writeback of delalloc blocks while
+ * the DIO was running we could fail to cleanup the orphan list in
+ * ext4_handle_inode_extension(). Do it now.
+ */
+ if (!list_empty(&EXT4_I(inode)->i_orphan) && inode->i_nlink) {
+ handle_t *handle = ext4_journal_start(inode, EXT4_HT_INODE, 2);
So this has to be called after the DIO write completes and calls
ext4_handle_inode_extension()?
....
@@ -606,9 +570,8 @@ static ssize_t ext4_dio_write_iter(struct kiocb *iocb, struct iov_iter *from)
dio_flags, NULL, 0);
if (ret == -ENOTBLK)
ret = 0;
-
if (extend)
- ret = ext4_handle_inode_extension(inode, offset, ret, count);
+ ext4_inode_extension_cleanup(inode, ret);
Because this doesn't wait for AIO DIO to complete and actually
extend the file before running the cleanup code...
As far as I know, for ext4 AIO DIO extension cases,
IOMAP_DIO_FORCE_WAIT will be set, thus no async DIO here.
So the timing for this case will be strictly:
- ext4_handle_inode_extension() --- record i_disksize in .end_io
- generic_write_sync() --- forcely do fsync()
- ext4_inode_extension_cleanup() --- drop orphan in another transaction
as mentioned in [1]
Anyway, that is my current limited thoughts.
[1] https://lore.kernel.org/linux-ext4/20230920152005.7iowrlukd5zbvp43@quack3/
Thanks,
Gao Xiang
Cheers,
Dave.
