drbd: only wakeup if something changed in update_peer_seq

This commit got it wrong:
    drbd: Make the peer_seq updating code more obvious

    Make it more clear that update_peer_seq() is supposed to wake up the
    seq_wait queue whenever the sequence number changes.

We don't need to wake up everytime we receive a sequence number
that is _different_ from our currently stored "newest" sequence number,
but only if we receive a sequence number _newer_ than what we already
have, when we actually change mdev->peer_seq.

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

1 files changed, 5 insertions, 4 deletions

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index e44bf3c25718..cd78ebfefe52 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -1734,14 +1734,15 @@ static bool need_peer_seq(struct drbd_conf *mdev)
 
 static void update_peer_seq(struct drbd_conf *mdev, unsigned int peer_seq)
 {
-        unsigned int old_peer_seq;
+        unsigned int newest_peer_seq;
 
         if (need_peer_seq(mdev)) {
                 spin_lock(&mdev->peer_seq_lock);
-                old_peer_seq = mdev->peer_seq;
-                mdev->peer_seq = seq_max(mdev->peer_seq, peer_seq);
+                newest_peer_seq = seq_max(mdev->peer_seq, peer_seq);
+                mdev->peer_seq = newest_peer_seq;
                 spin_unlock(&mdev->peer_seq_lock);
-                if (old_peer_seq != peer_seq)
+                /* wake up only if we actually changed mdev->peer_seq */
+                if (peer_seq == newest_peer_seq)
                         wake_up(&mdev->seq_wait);
         }
 }