drbd: Send P_NEG_ACK upon write error in protocol != C

In protocol != C, we forgot to send the P_NEG_ACK for failing writes.

Once we no longer submit to local disk, because we already "detached",
due to the typical "on-io-error detach;" config setting,
we already send the neg acks right away.

Only those requests that have been submitted,
and have been error-completed by the local disk,
would forget to send the neg-ack,
and only in asynchronous replication (protocol != C).
Unless this happened during resync,
where we already always send acks, regardless of protocol.

The primary side needs the P_NEG_ACK in order to mark
the affected block(s) for resync in its out-of-sync bitmap.

If the blocks in question are not re-written again,
we may miss to resync them later, causing data inconsistencies.

This patch will always send the neg-acks, and also at least try to
persist the out-of-sync status on the local node already.
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

drivers/block/drbd/drbd_worker.c

@@ -128,6 +128,14 @@ void drbd_endio_write_sec_final(struct drbd_peer_request *peer_req) __releases(l
 	block_id = peer_req->block_id;
 	peer_req->flags &= ~EE_CALL_AL_COMPLETE_IO;
 
+	if (peer_req->flags & EE_WAS_ERROR) {
+		/* In protocol != C, we usually do not send write acks.
+		 * In case of a write error, send the neg ack anyways. */
+		if (!__test_and_set_bit(__EE_SEND_WRITE_ACK, &peer_req->flags))
+			inc_unacked(device);
+		drbd_set_out_of_sync(device, peer_req->i.sector, peer_req->i.size);
+	}
+
 	spin_lock_irqsave(&device->resource->req_lock, flags);
 	device->writ_cnt += peer_req->i.size >> 9;
 	list_move_tail(&peer_req->w.list, &device->done_ee);