drbd: don't send out P_BARRIER with stale information

We must only send P_BARRIER for epochs we actually sent P_DATA in.

If we (re-)establish a connection, we reinitialized the
send.current_epoch_nr, but forgot to reset send.current_epoch_writes.

This could result in a spurious P_BARRIER with stale epoch information,
and a disconnect/reconnect cycle once the then "unexpected"
P_BARRIER_ACK is received:
  BAD! BarrierAck #28823 received, expected #28829!

Introduce re_init_if_first_write() and maybe_send_barrier() helpers,
and call them appropriately for read/write/set-out-of-sync requests.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>

diff --git a/drivers/block/drbd/drbd_worker.c b/drivers/block/drbd/drbd_worker.c
index 1c9c6fd..c674f17 100644 (file)
--- a/drivers/block/drbd/drbd_worker.c
+++ b/drivers/block/drbd/drbd_worker.c
@@ -1265,6 +1265,27 @@ int w_send_write_hint(struct drbd_work *w, int cancel)
        return drbd_send_command(mdev, sock, P_UNPLUG_REMOTE, 0, NULL, 0);
 }
 
+static void re_init_if_first_write(struct drbd_tconn *tconn, unsigned int epoch)
+{
+       if (!tconn->send.seen_any_write_yet) {
+               tconn->send.seen_any_write_yet = true;
+               tconn->send.current_epoch_nr = epoch;
+               tconn->send.current_epoch_writes = 0;
+       }
+}
+
+static void maybe_send_barrier(struct drbd_tconn *tconn, unsigned int epoch)
+{
+       /* re-init if first write on this connection */
+       if (!tconn->send.seen_any_write_yet)
+               return;
+       if (tconn->send.current_epoch_nr != epoch) {
+               if (tconn->send.current_epoch_writes)
+                       drbd_send_barrier(tconn);
+               tconn->send.current_epoch_nr = epoch;
+       }
+}
+
 int w_send_out_of_sync(struct drbd_work *w, int cancel)
 {
        struct drbd_request *req = container_of(w, struct drbd_request, w);
@@ -1277,19 +1298,11 @@ int w_send_out_of_sync(struct drbd_work *w, int cancel)
                return 0;
        }
 
-       if (!tconn->send.seen_any_write_yet) {
-               tconn->send.seen_any_write_yet = true;
-               tconn->send.current_epoch_nr = req->epoch;
-       }
-       if (tconn->send.current_epoch_nr != req->epoch) {
-               if (tconn->send.current_epoch_writes)
-                       drbd_send_barrier(tconn);
-               tconn->send.current_epoch_nr = req->epoch;
-       }
        /* this time, no tconn->send.current_epoch_writes++;
         * If it was sent, it was the closing barrier for the last
         * replicated epoch, before we went into AHEAD mode.
         * No more barriers will be sent, until we leave AHEAD mode again. */
+       maybe_send_barrier(tconn, req->epoch);
 
        err = drbd_send_out_of_sync(mdev, req);
        req_mod(req, OOS_HANDED_TO_NETWORK);
@@ -1315,15 +1328,8 @@ int w_send_dblock(struct drbd_work *w, int cancel)
                return 0;
        }
 
-       if (!tconn->send.seen_any_write_yet) {
-               tconn->send.seen_any_write_yet = true;
-               tconn->send.current_epoch_nr = req->epoch;
-       }
-       if (tconn->send.current_epoch_nr != req->epoch) {
-               if (tconn->send.current_epoch_writes)
-                       drbd_send_barrier(tconn);
-               tconn->send.current_epoch_nr = req->epoch;
-       }
+       re_init_if_first_write(tconn, req->epoch);
+       maybe_send_barrier(tconn, req->epoch);
        tconn->send.current_epoch_writes++;
 
        err = drbd_send_dblock(mdev, req);
@@ -1352,12 +1358,7 @@ int w_send_read_req(struct drbd_work *w, int cancel)
 
        /* Even read requests may close a write epoch,
         * if there was any yet. */
-       if (tconn->send.seen_any_write_yet &&
-           tconn->send.current_epoch_nr != req->epoch) {
-               if (tconn->send.current_epoch_writes)
-                       drbd_send_barrier(tconn);
-               tconn->send.current_epoch_nr = req->epoch;
-       }
+       maybe_send_barrier(tconn, req->epoch);
 
        err = drbd_send_drequest(mdev, P_DATA_REQUEST, req->i.sector, req->i.size,
                                 (unsigned long)req);