[PATCH 4.19 110/149] fuse: truncate pending writes on O_TRUNC

[Greg Kroah-Hartman]

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")
Cc: <stable@xxxxxxxxxxxxxxx> # v3.15+
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 fs/fuse/file.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -202,7 +202,7 @@ 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;
 
@@ -210,16 +210,20 @@ int fuse_open_common(struct inode *inode
 	if (err)
 		return err;
 
-	if (lock_inode)
+	if (is_wb_truncate) {
 		inode_lock(inode);
+		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);
 		inode_unlock(inode);
+	}
 
 	return err;
 }