ext4: honor O_(D)SYNC semantic in ext4_fallocate()

Ext4 must make sure the transaction to be commited to the disk when
user opens a file with O_(D)SYNC flag and do a fallocate(2) call.

This problem had been reported by Christoph Hellwig in this thread:
http://www.spinics.net/lists/linux-btrfs/msg13621.html

Reported-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Zheng Liu <wenqing.lz@taobao.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 91341ec6e06a..f1089cba913a 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4420,6 +4420,8 @@ retry:
                 ext4_falloc_update_inode(inode, mode, new_size,
                                          (map.m_flags & EXT4_MAP_NEW));
                 ext4_mark_inode_dirty(handle, inode);
+                if ((file->f_flags & O_SYNC) && ret >= max_blocks)
+                        ext4_handle_sync(handle);
                 ret2 = ext4_journal_stop(handle);
                 if (ret2)
                         break;