make sure data is on disk before calling ->write_inode

Similar to the fsync issue fixed a while ago in commit
2daea67e966dc0c42067ebea015ddac6834cef88 we need to write for data to
actually hit the disk before writing out the metadata to guarantee
data integrity for filesystems that modify the inode in the data I/O
completion path.  Currently XFS and NFS handle this manually, and AFS
has a write_inode method that does nothing but waiting for data, while
others are possibly missing out on this.

Fortunately this change has a lot less impact than the fsync change
as none of the write_inode methods starts data writeout of any form
by itself.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 10 insertions, 5 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1a7c42c..5f2721b 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -461,15 +461,20 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
 
 	ret = do_writepages(mapping, wbc);
 
-	/* Don't write the inode if only I_DIRTY_PAGES was set */
-	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
-		int err = write_inode(inode, wait);
+	/*
+	 * Make sure to wait on the data before writing out the metadata.
+	 * This is important for filesystems that modify metadata on data
+	 * I/O completion.
+	 */
+	if (wait) {
+		int err = filemap_fdatawait(mapping);
 		if (ret == 0)
 			ret = err;
 	}
 
-	if (wait) {
-		int err = filemap_fdatawait(mapping);
+	/* Don't write the inode if only I_DIRTY_PAGES was set */
+	if (dirty & (I_DIRTY_SYNC | I_DIRTY_DATASYNC)) {
+		int err = write_inode(inode, wait);
 		if (ret == 0)
 			ret = err;
 	}