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: c435ee34551e ("afs: Overhaul the callback handling")
Signed-off-by: David Howells <dhowells@redhat.com>
diff --git a/fs/afs/fsclient.c b/fs/afs/fsclient.c
index d16f26c..b273e1d 100644
--- a/fs/afs/fsclient.c
+++ b/fs/afs/fsclient.c
@@ -261,7 +261,7 @@ static void xdr_decode_AFSCallBack(struct afs_call *call,
 
 	write_seqlock(&vnode->cb_lock);
 
-	if (call->cb_break == (vnode->cb_break + cbi->server->cb_s_break)) {
+	if (call->cb_break == afs_cb_break_sum(vnode, cbi)) {
 		vnode->cb_version	= ntohl(*bp++);
 		cb_expiry		= ntohl(*bp++);
 		vnode->cb_type		= ntohl(*bp++);