[PATCH 3.16 086/136] fuse: truncate pending writes on O_TRUNC

[Ben Hutchings]

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@xxxxxxxxxx>

commit e4648309b85a78f8c787457832269a8712a8673e upstream.

Make sure cached writes are not reordered around open(..., O_TRUNC), with
the obvious wrong results.

Fixes: 4d99ff8f12eb ("fuse: Turn writeback cache on")
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 fs/fuse/file.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -237,7 +237,7 @@ int fuse_open_common(struct inode *inode
 {
 	struct fuse_conn *fc = get_fuse_conn(inode);
 	int err;
-	bool lock_inode = (file->f_flags & O_TRUNC) &&
+	bool is_wb_truncate = (file->f_flags & O_TRUNC) &&
 			  fc->atomic_o_trunc &&
 			  fc->writeback_cache;
 
@@ -245,16 +245,20 @@ int fuse_open_common(struct inode *inode
 	if (err)
 		return err;
 
-	if (lock_inode)
+	if (is_wb_truncate) {
 		mutex_lock(&inode->i_mutex);
+		fuse_set_nowrite(inode);
+	}
 
 	err = fuse_do_open(fc, get_node_id(inode), file, isdir);
 
 	if (!err)
 		fuse_finish_open(inode, file);
 
-	if (lock_inode)
+	if (is_wb_truncate) {
+		fuse_release_nowrite(inode);
 		mutex_unlock(&inode->i_mutex);
+	}
 
 	return err;
 }