afs: Fix whole-volume callback handling

It's possible for an AFS file server to issue a whole-volume notification
that callbacks on all the vnodes in the file have been broken.  This is
done for R/O and backup volumes (which don't have per-file callbacks) and
for things like a volume being taken offline.

Fix callback handling to detect whole-volume notifications, to track it
across operations and to check it during inode validation.

Fixes: c435ee3455 ("afs: Overhaul the callback handling")
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/super.c

@@ -688,7 +688,7 @@ static int afs_statfs(struct dentry *dentry, struct kstatfs *buf)
 	if (afs_begin_vnode_operation(&fc, vnode, key)) {
 		fc.flags |= AFS_FS_CURSOR_NO_VSLEEP;
 		while (afs_select_fileserver(&fc)) {
-			fc.cb_break = vnode->cb_break + vnode->cb_s_break;
+			fc.cb_break = afs_calc_vnode_cb_break(vnode);
 			afs_fs_get_volume_status(&fc, &vs);
 		}