drbd: fix drbd epoch write count for ahead/behind mode

The sanity check when receiving P_BARRIER_ACK does expect all write
requests with a given req->epoch to have been either all replicated,
or all not replicated.

Because req->epoch was assigned before calling maybe_pull_ahead(),
this expectation was not met, leading to an off-by-one in the sanity
check, and further to a "Protocol Error".

Fix: move the call to maybe_pull_ahead() a few lines up,
and assign req->epoch only after that.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/drivers/block/drbd/drbd_req.c b/drivers/block/drbd/drbd_req.c
index beefe65764ffc258aeaf6dc4108b2d1babf4e189..c24379ffd4e309cb0344f138854a131e12cc804e 100644 (file)
--- a/drivers/block/drbd/drbd_req.c
+++ b/drivers/block/drbd/drbd_req.c
@@ -865,8 +865,10 @@ static void maybe_pull_ahead(struct drbd_conf *mdev)
        bool congested = false;
        enum drbd_on_congestion on_congestion;
 
+       rcu_read_lock();
        nc = rcu_dereference(tconn->net_conf);
        on_congestion = nc ? nc->on_congestion : OC_BLOCK;
+       rcu_read_unlock();
        if (on_congestion == OC_BLOCK ||
            tconn->agreed_pro_version < 96)
                return;
@@ -960,14 +962,8 @@ static int drbd_process_write_request(struct drbd_request *req)
        struct drbd_conf *mdev = req->w.mdev;
        int remote, send_oos;
 
-       rcu_read_lock();
        remote = drbd_should_do_remote(mdev->state);
-       if (remote) {
-               maybe_pull_ahead(mdev);
-               remote = drbd_should_do_remote(mdev->state);
-       }
        send_oos = drbd_should_send_out_of_sync(mdev->state);
-       rcu_read_unlock();
 
        /* Need to replicate writes.  Unless it is an empty flush,
         * which is better mapped to a DRBD P_BARRIER packet,
@@ -1087,9 +1083,13 @@ static void drbd_send_and_submit(struct drbd_conf *mdev, struct drbd_request *re
                 * but will re-aquire it before it returns here.
                 * Needs to be before the check on drbd_suspended() */
                complete_conflicting_writes(req);
+               /* no more giving up req_lock from now on! */
+
+               /* check for congestion, and potentially stop sending
+                * full data updates, but start sending "dirty bits" only. */
+               maybe_pull_ahead(mdev);
        }
 
-       /* no more giving up req_lock from now on! */
 
        if (drbd_suspended(mdev)) {
                /* push back and retry: */