drbd: Improve compatibility with drbd's older than 8.3.7

Regression introduced with 8.3.11 commit:
drbd: Take a more conservative approach when deciding max_bio_size

Never ever tell an older drbd, that we support more than 32KiB
in a single data request (packet).
Never believe an older drbd, that is supports more than 32KiB
in a single data request (packet)

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

2 files changed, 8 insertions, 3 deletions

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 8e83a402ed5c..a15135b9b60a 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2112,6 +2112,10 @@ int drbd_send_sizes(struct drbd_conf *mdev, int trigger_reply, enum dds_flags fl
                 max_bio_size = DRBD_MAX_BIO_SIZE; /* ... multiple BIOs per peer_request */
         }
 
+        /* Never allow old drbd (up to 8.3.7) to see more than 32KiB */
+        if (mdev->agreed_pro_version <= 94)
+                max_bio_size = min_t(int, max_bio_size, DRBD_MAX_SIZE_H80_PACKET);
+
         p.d_size = cpu_to_be64(d_size);
         p.u_size = cpu_to_be64(u_size);
         p.c_size = cpu_to_be64(trigger_reply ? 0 : drbd_get_capacity(mdev->this_bdev));
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index f7b5f7e86a57..cabad39f908c 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -845,9 +845,10 @@ void drbd_reconsider_max_bio_size(struct drbd_conf *mdev)
            Because new from 8.3.8 onwards the peer can use multiple
            BIOs for a single peer_request */
         if (mdev->state.conn >= C_CONNECTED) {
-                if (mdev->agreed_pro_version < 94)
-                        peer = mdev->peer_max_bio_size;
-                else if (mdev->agreed_pro_version == 94)
+                if (mdev->agreed_pro_version < 94) {
+                        peer = min_t(int, mdev->peer_max_bio_size, DRBD_MAX_SIZE_H80_PACKET);
+                        /* Correct old drbd (up to 8.3.7) if it believes it can do more than 32KiB */
+                } else if (mdev->agreed_pro_version == 94)
                         peer = DRBD_MAX_SIZE_H80_PACKET;
                 else /* drbd 8.3.8 onwards */
                         peer = DRBD_MAX_BIO_SIZE;