fuse: add missing FR_FORCE

commit 2e38bea9 upstream.

fuse_file_put() was missing the "force" flag for the RELEASE request when
sending synchronously (fuseblk).

If this flag is not set, then a sync request may be interrupted before it
is dequeued by the userspace filesystem.  In this case the OPEN won't be
balanced with a RELEASE.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 5a18ec17 ("fuse: fix hang of single threaded fuseblk filesystem")
[bwh: Backported to 3.16:
 - "force" flag is a bitfield
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/fuse/file.c

@@ -136,6 +136,7 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
 			path_put(&req->misc.release.path);
 			fuse_put_request(ff->fc, req);
 		} else if (sync) {
+			req->force = 1;
 			req->background = 0;
 			fuse_request_send(ff->fc, req);
 			path_put(&req->misc.release.path);